Develop Reference

Using a Coroutine in a loop

I have a question about coroutines in a loop. More specific about how I can achieve it that my loop continues to check the condition until the waitForSeconds in the coroutine are over.
I have attached a screenshot of my code. My problem is that the Line "Now I am executed" is shown right after myAudio.Play();
It makes sense since the coroutine only waits for the statements after the yield return but how can I make it work with the for loop?
Any help would be appreciated! Thank you so much.

StartCoroutine starts each IEnumeratoras a new Coroutine and immediately continuous with the rest of the code.
So as said without having further context of your code what you would do is something like
private void playDBStack()
{
fillList();
StartCoroutine(playDBStackRoutine())
}
private IEnumerator playDBStackRoutine()
{
for(var i = 0; i < 2; i++)
{
// executes playAudio and waits for it to finish
yield return playAudio();
}
}
private IEnumerator playAudio()
{
var x = chooseList(score);
// executes PlayAndWait and wait for it to finish
yield return PlayAndWait(x);
}
this way you execute and at the same time wait until the IEnumerators are finished before going to the next one.
Some further notes:
The line
myAudio.GetComponent<AudioSource>();
does absolutely nothing.
The entire method updateScore in its current state could simply be replaced by using
score++;
I would consider a method that can be replaced by a simple operator "code smell" ;)

Trouble understanding Delays and Coroutines

void start()
StartCoroutine(Text());
IEnumerator Text()
{
Debug.Log("Hello")
yield return new WaitForSeconds(3)
Debug.Log("ByeBye")
}
I understand the basic concept that this does but I don't get what anything means such as yield return new WaitforSeconds(3) and what StartCoroutine is and What an IEnumerator is.
Can anyone explain to me what they mean?

When you call a function, it runs to completion before returning. This effectively means that any action taking place in a function must happen within a single frame update; a function call can’t be used to contain a procedural animation or a sequence of events over time. As an example, consider the task of gradually reducing an object’s alpha (opacity) value until it becomes completely invisible.
void Fade()
{
for (float ft = 1f; ft >= 0; ft -= 0.1f)
{
Color c = renderer.material.color;
c.a = ft;
renderer.material.color = c;
}
}
As it stands, the Fade function will not have the effect you might expect. In order for the fading to be visible, the alpha must be reduced over a sequence of frames to show the intermediate values being rendered. However, the function will execute in its entirety within a single frame update. The intermediate values will never be seen and the object will disappear instantly.
It is possible to handle situations like this by adding code to the Update function that executes the fade on a frame-by-frame basis. However, it is often more convenient to use a coroutine for this kind of task.
A coroutine is like a function that has the ability to pause execution and return control to Unity but then to continue where it left off on the following frame. In C#, a coroutine is declared like this:
IEnumerator Fade()
{
for (float ft = 1f; ft >= 0; ft -= 0.1f)
{
Color c = renderer.material.color;
c.a = ft;
renderer.material.color = c;
yield return null;
}
}
It is essentially a function declared with a return type of IEnumerator and with the yield return statement included somewhere in the body. The yield return null line is the point at which execution will pause and be resumed the following frame. To set a coroutine running, you need to use the StartCoroutine function:
void Update()
{
if (Input.GetKeyDown("f"))
{
StartCoroutine("Fade");
}
}
You will notice that the loop counter in the Fade function maintains its correct value over the lifetime of the coroutine. In fact any variable or parameter will be correctly preserved between yields.
By default, a coroutine is resumed on the frame after it yields but it is also possible to introduce a time delay using WaitForSeconds:
IEnumerator Fade()
{
for (float ft = 1f; ft >= 0; ft -= 0.1f)
{
Color c = renderer.material.color;
c.a = ft;
renderer.material.color = c;
yield return new WaitForSeconds(.1f);
}
}
This can be used as a way to spread an effect over a period of time, but it is also a useful optimization. Many tasks in a game need to be carried out periodically and the most obvious way to do this is to include them in the Update function. However, this function will typically be called many times per second. When a task doesn’t need to be repeated quite so frequently, you can put it in a coroutine to get an update regularly but not every single frame. An example of this might be an alarm that warns the player if an enemy is nearby. The code might look something like this:
bool ProximityCheck()
{
for (int i = 0; i < enemies.Length; i++)
{
if (Vector3.Distance(transform.position, enemies[i].transform.position) < dangerDistance) {
return true;
}
}
return false;
}
If there are a lot of enemies then calling this function every frame might introduce a significant overhead. However, you could use a coroutine to call it every tenth of a second:
IEnumerator DoCheck()
{
for(;;)
{
ProximityCheck();
yield return new WaitForSeconds(.1f);
}
}
This would greatly reduce the number of checks carried out without any noticeable effect on gameplay.
Note: You can stop a Coroutine with StopCoroutine and StopAllCoroutines. A coroutines also stops when the GameObject it is attached to is disabled with SetActive(false). Calling Destroy(example) (where example is a MonoBehaviour instance) immediately triggers OnDisable and the coroutine is processed, effectively stopping it. Finally, OnDestroy is invoked at the end of the frame.
Coroutines are not stopped when disabling a MonoBehaviour by setting enabled to false on a MonoBehaviour instance.
Reference: https://docs.unity3d.com/Manual/Coroutines.html

Unity (ab)uses enumerators to build C# CoRoutines, because async / await didn't exist. When you write;
IEnumerator Text()
{
Debug.Log("Hello")
yield return new WaitForSeconds(3)
Debug.Log("ByeBye")
}
The compiler turns that into something like;
IEnumerator Text() => new StateMachine();
public class StateMachine : IEnumerable{
private int state = 0;
// plus any local variables moved to fields.
StateMachine(){}
public object Current { get; set; }
public bool MoveNext(){
switch(state){
case 0:
Debug.Log("Hello");
Current = new WaitForSeconds(3);
state = 1;
return true;
case 1:
Debug.Log("ByeBye");
return false;
}
}
}
Since the state of your function is now stored in fields on an object, your method can pause before it finishes. Unity will then look at the object you yield to decide when to call MoveNext().
Now that C# has async methods, which also cause your methods to be translated into state machines. It would be possible for a new version of unity to support them instead, like;
async Task Text()
{
Debug.Log("Hello")
await Something.WaitForSeconds(3)
Debug.Log("ByeBye")
}
But they would still have to support the old way of building CoRoutines.

Error: IsObjectMonoBehaviour can only be called from the main thread [duplicate]

My problem is I try to use Unity socket to implement something. Each time, when I get a new message I need to update it to the updattext (it is a Unity Text). However, When I do the following code, the void update does not calling every time.
The reason for I do not include updatetext.GetComponent<Text>().text = "From server: "+tempMesg;in the void getInformation is this function is in the thread, when I include that in getInformation() it will come with an error:
getcomponentfastpath can only be called from the main thread
I think the problem is I don't know how to run the main thread and the child thread in C# together? Or there maybe other problems.
Here is my code:
using UnityEngine;
using System.Collections;
using System;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using UnityEngine.UI;
public class Client : MonoBehaviour {
System.Net.Sockets.TcpClient clientSocket = new System.Net.Sockets.TcpClient();
private Thread oThread;
// for UI update
public GameObject updatetext;
String tempMesg = "Waiting...";
// Use this for initialization
void Start () {
updatetext.GetComponent<Text>().text = "Waiting...";
clientSocket.Connect("10.132.198.29", 8888);
oThread = new Thread (new ThreadStart (getInformation));
oThread.Start ();
Debug.Log ("Running the client");
}
// Update is called once per frame
void Update () {
updatetext.GetComponent<Text>().text = "From server: "+tempMesg;
Debug.Log (tempMesg);
}
void getInformation(){
while (true) {
try {
NetworkStream networkStream = clientSocket.GetStream ();
byte[] bytesFrom = new byte[10025];
networkStream.Read (bytesFrom, 0, (int)bytesFrom.Length);
string dataFromClient = System.Text.Encoding.ASCII.GetString (bytesFrom);
dataFromClient = dataFromClient.Substring (0, dataFromClient.IndexOf ("$"));
Debug.Log (" >> Data from Server - " + dataFromClient);
tempMesg = dataFromClient;
string serverResponse = "Last Message from Server" + dataFromClient;
Byte[] sendBytes = Encoding.ASCII.GetBytes (serverResponse);
networkStream.Write (sendBytes, 0, sendBytes.Length);
networkStream.Flush ();
Debug.Log (" >> " + serverResponse);
} catch (Exception ex) {
Debug.Log ("Exception error:" + ex.ToString ());
oThread.Abort ();
oThread.Join ();
}
// Thread.Sleep (500);
}
}
}

Unity is not Thread safe, so they decided to make it impossible to call their API from another Thread by adding a mechanism to throw an exception when its API is used from another Thread.
This question has been asked so many times, but there have been no proper solution/answer to any of them. The answers are usually "use a plugin" or do something not thread-safe. Hopefully, this will be the last one.
The solution you will usually see on Stackoverflow or Unity's forum website is to simply use a boolean variable to let the main thread know that you need to execute code in the main Thread. This is not right as it is not thread-safe and does not give you control to provide which function to call. What if you have multiple Threads that need to notify the main thread?
Another solution you will see is to use a coroutine instead of a Thread. This does not work. Using coroutine for sockets will not change anything. You will still end up with your freezing problems. You must stick with your Thread code or use Async.
One of the proper ways to do this is to create a collection such as List. When you need something to be executed in the main Thread, call a function that stores the code to execute in an Action. Copy that List of Action to a local List of Action then execute the code from the local Action in that List then clear that List. This prevents other Threads from having to wait for it to finish executing.
You also need to add a volatile boolean to notify the Update function that there is code waiting in the List to be executed. When copying the List to a local List, that should be wrapped around the lock keyword to prevent another Thread from writing to it.
A script that performs what I mentioned above:
UnityThread Script:
#define ENABLE_UPDATE_FUNCTION_CALLBACK
#define ENABLE_LATEUPDATE_FUNCTION_CALLBACK
#define ENABLE_FIXEDUPDATE_FUNCTION_CALLBACK
using System;
using System.Collections;
using UnityEngine;
using System.Collections.Generic;
public class UnityThread : MonoBehaviour
{
//our (singleton) instance
private static UnityThread instance = null;
////////////////////////////////////////////////UPDATE IMPL////////////////////////////////////////////////////////
//Holds actions received from another Thread. Will be coped to actionCopiedQueueUpdateFunc then executed from there
private static List<System.Action> actionQueuesUpdateFunc = new List<Action>();
//holds Actions copied from actionQueuesUpdateFunc to be executed
List<System.Action> actionCopiedQueueUpdateFunc = new List<System.Action>();
// Used to know if whe have new Action function to execute. This prevents the use of the lock keyword every frame
private volatile static bool noActionQueueToExecuteUpdateFunc = true;
////////////////////////////////////////////////LATEUPDATE IMPL////////////////////////////////////////////////////////
//Holds actions received from another Thread. Will be coped to actionCopiedQueueLateUpdateFunc then executed from there
private static List<System.Action> actionQueuesLateUpdateFunc = new List<Action>();
//holds Actions copied from actionQueuesLateUpdateFunc to be executed
List<System.Action> actionCopiedQueueLateUpdateFunc = new List<System.Action>();
// Used to know if whe have new Action function to execute. This prevents the use of the lock keyword every frame
private volatile static bool noActionQueueToExecuteLateUpdateFunc = true;
////////////////////////////////////////////////FIXEDUPDATE IMPL////////////////////////////////////////////////////////
//Holds actions received from another Thread. Will be coped to actionCopiedQueueFixedUpdateFunc then executed from there
private static List<System.Action> actionQueuesFixedUpdateFunc = new List<Action>();
//holds Actions copied from actionQueuesFixedUpdateFunc to be executed
List<System.Action> actionCopiedQueueFixedUpdateFunc = new List<System.Action>();
// Used to know if whe have new Action function to execute. This prevents the use of the lock keyword every frame
private volatile static bool noActionQueueToExecuteFixedUpdateFunc = true;
//Used to initialize UnityThread. Call once before any function here
public static void initUnityThread(bool visible = false)
{
if (instance != null)
{
return;
}
if (Application.isPlaying)
{
// add an invisible game object to the scene
GameObject obj = new GameObject("MainThreadExecuter");
if (!visible)
{
obj.hideFlags = HideFlags.HideAndDontSave;
}
DontDestroyOnLoad(obj);
instance = obj.AddComponent<UnityThread>();
}
}
public void Awake()
{
DontDestroyOnLoad(gameObject);
}
//////////////////////////////////////////////COROUTINE IMPL//////////////////////////////////////////////////////
#if (ENABLE_UPDATE_FUNCTION_CALLBACK)
public static void executeCoroutine(IEnumerator action)
{
if (instance != null)
{
executeInUpdate(() => instance.StartCoroutine(action));
}
}
////////////////////////////////////////////UPDATE IMPL////////////////////////////////////////////////////
public static void executeInUpdate(System.Action action)
{
if (action == null)
{
throw new ArgumentNullException("action");
}
lock (actionQueuesUpdateFunc)
{
actionQueuesUpdateFunc.Add(action);
noActionQueueToExecuteUpdateFunc = false;
}
}
public void Update()
{
if (noActionQueueToExecuteUpdateFunc)
{
return;
}
//Clear the old actions from the actionCopiedQueueUpdateFunc queue
actionCopiedQueueUpdateFunc.Clear();
lock (actionQueuesUpdateFunc)
{
//Copy actionQueuesUpdateFunc to the actionCopiedQueueUpdateFunc variable
actionCopiedQueueUpdateFunc.AddRange(actionQueuesUpdateFunc);
//Now clear the actionQueuesUpdateFunc since we've done copying it
actionQueuesUpdateFunc.Clear();
noActionQueueToExecuteUpdateFunc = true;
}
// Loop and execute the functions from the actionCopiedQueueUpdateFunc
for (int i = 0; i < actionCopiedQueueUpdateFunc.Count; i++)
{
actionCopiedQueueUpdateFunc[i].Invoke();
}
}
#endif
////////////////////////////////////////////LATEUPDATE IMPL////////////////////////////////////////////////////
#if (ENABLE_LATEUPDATE_FUNCTION_CALLBACK)
public static void executeInLateUpdate(System.Action action)
{
if (action == null)
{
throw new ArgumentNullException("action");
}
lock (actionQueuesLateUpdateFunc)
{
actionQueuesLateUpdateFunc.Add(action);
noActionQueueToExecuteLateUpdateFunc = false;
}
}
public void LateUpdate()
{
if (noActionQueueToExecuteLateUpdateFunc)
{
return;
}
//Clear the old actions from the actionCopiedQueueLateUpdateFunc queue
actionCopiedQueueLateUpdateFunc.Clear();
lock (actionQueuesLateUpdateFunc)
{
//Copy actionQueuesLateUpdateFunc to the actionCopiedQueueLateUpdateFunc variable
actionCopiedQueueLateUpdateFunc.AddRange(actionQueuesLateUpdateFunc);
//Now clear the actionQueuesLateUpdateFunc since we've done copying it
actionQueuesLateUpdateFunc.Clear();
noActionQueueToExecuteLateUpdateFunc = true;
}
// Loop and execute the functions from the actionCopiedQueueLateUpdateFunc
for (int i = 0; i < actionCopiedQueueLateUpdateFunc.Count; i++)
{
actionCopiedQueueLateUpdateFunc[i].Invoke();
}
}
#endif
////////////////////////////////////////////FIXEDUPDATE IMPL//////////////////////////////////////////////////
#if (ENABLE_FIXEDUPDATE_FUNCTION_CALLBACK)
public static void executeInFixedUpdate(System.Action action)
{
if (action == null)
{
throw new ArgumentNullException("action");
}
lock (actionQueuesFixedUpdateFunc)
{
actionQueuesFixedUpdateFunc.Add(action);
noActionQueueToExecuteFixedUpdateFunc = false;
}
}
public void FixedUpdate()
{
if (noActionQueueToExecuteFixedUpdateFunc)
{
return;
}
//Clear the old actions from the actionCopiedQueueFixedUpdateFunc queue
actionCopiedQueueFixedUpdateFunc.Clear();
lock (actionQueuesFixedUpdateFunc)
{
//Copy actionQueuesFixedUpdateFunc to the actionCopiedQueueFixedUpdateFunc variable
actionCopiedQueueFixedUpdateFunc.AddRange(actionQueuesFixedUpdateFunc);
//Now clear the actionQueuesFixedUpdateFunc since we've done copying it
actionQueuesFixedUpdateFunc.Clear();
noActionQueueToExecuteFixedUpdateFunc = true;
}
// Loop and execute the functions from the actionCopiedQueueFixedUpdateFunc
for (int i = 0; i < actionCopiedQueueFixedUpdateFunc.Count; i++)
{
actionCopiedQueueFixedUpdateFunc[i].Invoke();
}
}
#endif
public void OnDisable()
{
if (instance == this)
{
instance = null;
}
}
}
USAGE:
This implementation allows you to call functions in the 3 most used Unity functions: Update, LateUpdate and FixedUpdate functions. This also allows you call run a coroutine function in the main Thread. It can be extended to be able to call functions in other Unity callback functions such as OnPreRender and OnPostRender.
1.First, initialize it from the Awake() function.
void Awake()
{
UnityThread.initUnityThread();
}
2.To execute a code in the main Thread from another Thread:
UnityThread.executeInUpdate(() =>
{
transform.Rotate(new Vector3(0f, 90f, 0f));
});
This will rotate the current Object the scipt is attached to, to 90 deg. You can now use Unity API(transform.Rotate) in another Thread.
3.To call a function in the main Thread from another Thread:
Action rot = Rotate;
UnityThread.executeInUpdate(rot);
void Rotate()
{
transform.Rotate(new Vector3(0f, 90f, 0f));
}
The #2 and #3 samples executes in the Update function.
4.To execute a code in the LateUpdate function from another Thread:
Example of this is a camera tracking code.
UnityThread.executeInLateUpdate(()=>
{
//Your code camera moving code
});
5.To execute a code in the FixedUpdate function from another Thread:
Example of this when doing physics stuff such as adding force to Rigidbody.
UnityThread.executeInFixedUpdate(()=>
{
//Your code physics code
});
6.To Start a coroutine function in the main Thread from another Thread:
UnityThread.executeCoroutine(myCoroutine());
IEnumerator myCoroutine()
{
Debug.Log("Hello");
yield return new WaitForSeconds(2f);
Debug.Log("Test");
}
Finally, if you don't need to execute anything in the LateUpdate and FixedUpdate functions, you should comment both lines of this code below:
//#define ENABLE_LATEUPDATE_FUNCTION_CALLBACK
//#define ENABLE_FIXEDUPDATE_FUNCTION_CALLBACK
This will increase performance.

I have been using this solution to this problem. Create a script with this code and attach it to a Game Object:
using System;
using System.Collections.Generic;
using System.Collections.Concurrent;
using UnityEngine;
public class ExecuteOnMainThread : MonoBehaviour {
public static readonly ConcurrentQueue<Action> RunOnMainThread = new ConcurrentQueue<Action>();
void Update()
{
if(!RunOnMainThread.IsEmpty)
{
while(RunOnMainThread.TryDequeue(out var action))
{
action?.Invoke();
}
}
}
}
Then when you need to call something on the main thread and access the Unity API from any other function in your application:
ExecuteOnMainThread.RunOnMainThread.Enqueue(() => {
// Code here will be called in the main thread...
});

Much of the writing about threads in Unity is incorrect.
How so?
Unity is, of course, totally frame-based.
When you work in a frame-based system, threading issues are completely different.
Threading issues on a frame-based system are completely different. (In fact, often much easier to deal with.)
Let's say you have a Unity thermometer display that shows some value
Thermo.cs
So it will have a function which is called in Update, like
func void ShowThermoValue(float fraction) {
display code to show the current thermometer value
}
Recall that the "Update" function in Unity simply means "run this once each frame".
That only runs once per frame, and that's that.
(Naturally, it runs only on the "main thread". There's nothing else in Unity! There's just ... "the Unity thread"!)
Somewhere else, perhaps in "IncomingData.cs", you will have a function which handles the concept "a new value has arrived":
[MonoPInvokeCallback(typeof(ipDel))]
public static void NewValueArrives(float f) {
... ???
}
Note that, of course, that is a class function! What else can it be?
You can't "reach in to" a normal Unity function. (Such as ShowThermoValue.) That would be meaningless - it's just a function which runs once each frame.Footnote 1
Let's say: values arrive very frequently and irregularly.
Image you have some sort of scientific devices (perhaps IR thermometers) connected connected to a rack of PCs
Those electronic devices deliver new "temperature" values very often. Let's say dozens of times per frame.
So, "NewValueArrives" is being called 100s of times a second.
So what do you do with the values?
It could not be simpler.
From the arriving-values thread, all you do is ................. wait for it ............. set a variable in the component!!
WTF? All you do is set a variable? That's it? How can it be that simple?
This is one of those unusual situations:
Much of the writing on threads in Unity is, simply, completely hopeless.
Surprisingly, the actual approach is extremely simple.
It's so simple you may think you are doing something wrong!!
So have the variable ...
[System.Nonserialized] public float latestValue;
Set it from the "arriving thread" ...
[MonoPInvokeCallback(typeof(ipDel))]
public static void NewValueArrives(float f) {
ThisScript.runningInstance.latestValue = f; // done
}
Honestly that's it.
Essentially, to be the world's greatest expert at "threading in Unity" - which is, obviously, frame-based - there's nothing more to do than the above.
And whenever ShowThermoValue is called each frame ...................... simply display that value!
Really, that's it!
[System.Nonserialized] public float latestValue;
func void ShowThermoValue() { // note NO arguments here!
display code, draws a thermometer
thermo height = latestValue
}
You're simply displaying the "latest" value.
latestValue may have been set once, twice, ten times, or a hundred times that frame ............ but, you simply display whatever is the value when ShowThermoValue runs that frame!
What else could you display?
The thermometer is updating at 60fps on-screen so you display the latest value. Footnote 2
It's actually that easy. It's just that easy. Surprising but true.
#(Critical aside - don't forget that vector3, etc, are NOT Atomic in Unity/C#)
As user #dymanoid has pointed out (read the important discussion below) it's critical to remember that while float is atomic in the Unity/C# milieu, anything else (say, Vector3 etc) IS NOT ATOMIC. Typically (as in the example here) you only pass floats around from calculations from, say, native plugins, thermometers etc. But it's essential to be aware that vectors and so on are NOT atomic.
Sometimes experienced threading programmers get in a knot with a frame-based system, because: in a frame based system most of the problems caused by racetrack and locking issues ... do not exist conceptually.
In a frame-based system, any game items should simply be displaying or behaving based on some "current value," which is set somewhere. If you have info arriving from other threads, just set those values - you're done.
You can not meaningfully "talk to the main thread" in Unity because that main thread ............. is frame-based!
Most locking, blocking and racetrack issues are non-existent in the frame-based paradigm because: if you set latestValue ten times, a million times, a billion times, in one particular frame .. what can you do? .. you can only display one value during that frame!
Think of an old-fashioned plastic film. You literally just have ...... a frame, and that's it. If you set latestValue a trillion times in one particular frame, ShowThermoValue will simply display (for that 60th of a second) the one value it grabs when it is run.
All you do is: leave information somewhere, which, the frame-paradigm system will utilize during that frame if it wants to.
That's it in a nutshell.
Thus, most "threading issues" disappear in Unity.
All you can do from
other calculation threads or
from plugin threads,
is just "drop-off values" which the game may use.
That's it!
Let's consider the question title...
How do you "... call a function in the main Thread"
This is completely meaningless. The "functions" in Unity are simply functions which the frame engine runs once per frame.
You can't "call" anything in Unity. The frame engine runs a number of things (many things) once per frame.
Note that indeed threads are totally irrelevant. If Unity ran with a billion threads, or with quantum computing, it would have no bearing on anything.
You can't "call a function" in a frame-based system.
Fortunately, the approach to take is dead simple, you just set values, which the frame-based functions can look at when they want! It's really that easy.
Footnotes
1 How could you? As a thought experiment, forget about the issue that you're on a different thread. ShowThermoValue is run once a frame by the frame engine. You can't "call" it in any meaningful way. Unlike in normal OO software, you cannot, say, instantiate an instance of the class (a Component?? meaningless) and run that function - that is completely meaningless.
In "normal" threaded programming, threads can talk back and fore and so on, and in doing so you have concerns about locking, racetrack and so on. But that is all meaningless in an ECS, frame-based, system. There is nothing to "talk to".
Let's say that Unity was in fact multithreaded!!!! So the Unity guys have all of the engine running in a multithreaded manner. It wouldn't make any difference - you can not get "in to" ShowThermoValue in any meaningful way! It's a Component which the frame engine runs once a frame and that's that.
So NewValueArrives is not anywhere - it's a class function!
Let's answer the question in the headline:
"Use Unity API from another Thread or call a function in the main Thread?"
The concept is >> completely meaningless <<. Unity (like all game engines) is frame-based. There's no concept of "calling" a function on the main thread. To make an analogy: it would be like a cinematographer in the celluloid-film era asking how to "move" something actually on one of the frames.
Of course that is meaningless. All you can do is change something for the next photo, the next frame.
2 I refer to the "arriving-values thread" ... in fact! NewValueArrives may, or may not, run on the main thread!!!! It may run on the thread of the plugin, or on some other thread! It may actually be completely single-threaded by the time you deal with the NewValueArrives call! It just doesn't matter! What you do, and all you can do, in a frame-based paradigm, is, "leave laying around" information which Components such as ShowThermoValue, may use, as, they see fit.

Another solution to run code on the main thread, but without requiring a game object and MonoBehavior, is to use SynchronizationContext:
// On main thread, during initialization:
var syncContext = System.Threading.SynchronizationContext.Current;
// On your worker thread
syncContext.Post(_ =>
{
// This code here will run on the main thread
Debug.Log("Hello from main thread!");
}, null);

Use UniRx's multithreading pattern, UniTask and RxSocket together.
[SerializeField] private Text m_Text;
async UniTaskVoid Connect() {
IPEndPoint endPoint = new IPEndPoint(IPAddress.IPv6Loopback, 12345);
// Create a socket client by connecting to the server at the IPEndPoint.
// See the UniRx Async tooling to use await
IRxSocketClient client = await endPoint.ConnectRxSocketClientAsync();
client.ReceiveObservable
.ToStrings()
.ObserveOnMainThread()
.Subscribe(onNext: message =>
{
m_Text.text = message;
}).AddTo(this);
// Send a message to the server.
client.Send("Hello!".ToByteArray());
}

TCP SocketServer works but does not execute on Main Thread (Unity) [duplicate]

My problem is I try to use Unity socket to implement something. Each time, when I get a new message I need to update it to the updattext (it is a Unity Text). However, When I do the following code, the void update does not calling every time.
The reason for I do not include updatetext.GetComponent<Text>().text = "From server: "+tempMesg;in the void getInformation is this function is in the thread, when I include that in getInformation() it will come with an error:
getcomponentfastpath can only be called from the main thread
I think the problem is I don't know how to run the main thread and the child thread in C# together? Or there maybe other problems.
Here is my code:
using UnityEngine;
using System.Collections;
using System;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using UnityEngine.UI;
public class Client : MonoBehaviour {
System.Net.Sockets.TcpClient clientSocket = new System.Net.Sockets.TcpClient();
private Thread oThread;
// for UI update
public GameObject updatetext;
String tempMesg = "Waiting...";
// Use this for initialization
void Start () {
updatetext.GetComponent<Text>().text = "Waiting...";
clientSocket.Connect("10.132.198.29", 8888);
oThread = new Thread (new ThreadStart (getInformation));
oThread.Start ();
Debug.Log ("Running the client");
}
// Update is called once per frame
void Update () {
updatetext.GetComponent<Text>().text = "From server: "+tempMesg;
Debug.Log (tempMesg);
}
void getInformation(){
while (true) {
try {
NetworkStream networkStream = clientSocket.GetStream ();
byte[] bytesFrom = new byte[10025];
networkStream.Read (bytesFrom, 0, (int)bytesFrom.Length);
string dataFromClient = System.Text.Encoding.ASCII.GetString (bytesFrom);
dataFromClient = dataFromClient.Substring (0, dataFromClient.IndexOf ("$"));
Debug.Log (" >> Data from Server - " + dataFromClient);
tempMesg = dataFromClient;
string serverResponse = "Last Message from Server" + dataFromClient;
Byte[] sendBytes = Encoding.ASCII.GetBytes (serverResponse);
networkStream.Write (sendBytes, 0, sendBytes.Length);
networkStream.Flush ();
Debug.Log (" >> " + serverResponse);
} catch (Exception ex) {
Debug.Log ("Exception error:" + ex.ToString ());
oThread.Abort ();
oThread.Join ();
}
// Thread.Sleep (500);
}
}
}

Unity is not Thread safe, so they decided to make it impossible to call their API from another Thread by adding a mechanism to throw an exception when its API is used from another Thread.
This question has been asked so many times, but there have been no proper solution/answer to any of them. The answers are usually "use a plugin" or do something not thread-safe. Hopefully, this will be the last one.
The solution you will usually see on Stackoverflow or Unity's forum website is to simply use a boolean variable to let the main thread know that you need to execute code in the main Thread. This is not right as it is not thread-safe and does not give you control to provide which function to call. What if you have multiple Threads that need to notify the main thread?
Another solution you will see is to use a coroutine instead of a Thread. This does not work. Using coroutine for sockets will not change anything. You will still end up with your freezing problems. You must stick with your Thread code or use Async.
One of the proper ways to do this is to create a collection such as List. When you need something to be executed in the main Thread, call a function that stores the code to execute in an Action. Copy that List of Action to a local List of Action then execute the code from the local Action in that List then clear that List. This prevents other Threads from having to wait for it to finish executing.
You also need to add a volatile boolean to notify the Update function that there is code waiting in the List to be executed. When copying the List to a local List, that should be wrapped around the lock keyword to prevent another Thread from writing to it.
A script that performs what I mentioned above:
UnityThread Script:
#define ENABLE_UPDATE_FUNCTION_CALLBACK
#define ENABLE_LATEUPDATE_FUNCTION_CALLBACK
#define ENABLE_FIXEDUPDATE_FUNCTION_CALLBACK
using System;
using System.Collections;
using UnityEngine;
using System.Collections.Generic;
public class UnityThread : MonoBehaviour
{
//our (singleton) instance
private static UnityThread instance = null;
////////////////////////////////////////////////UPDATE IMPL////////////////////////////////////////////////////////
//Holds actions received from another Thread. Will be coped to actionCopiedQueueUpdateFunc then executed from there
private static List<System.Action> actionQueuesUpdateFunc = new List<Action>();
//holds Actions copied from actionQueuesUpdateFunc to be executed
List<System.Action> actionCopiedQueueUpdateFunc = new List<System.Action>();
// Used to know if whe have new Action function to execute. This prevents the use of the lock keyword every frame
private volatile static bool noActionQueueToExecuteUpdateFunc = true;
////////////////////////////////////////////////LATEUPDATE IMPL////////////////////////////////////////////////////////
//Holds actions received from another Thread. Will be coped to actionCopiedQueueLateUpdateFunc then executed from there
private static List<System.Action> actionQueuesLateUpdateFunc = new List<Action>();
//holds Actions copied from actionQueuesLateUpdateFunc to be executed
List<System.Action> actionCopiedQueueLateUpdateFunc = new List<System.Action>();
// Used to know if whe have new Action function to execute. This prevents the use of the lock keyword every frame
private volatile static bool noActionQueueToExecuteLateUpdateFunc = true;
////////////////////////////////////////////////FIXEDUPDATE IMPL////////////////////////////////////////////////////////
//Holds actions received from another Thread. Will be coped to actionCopiedQueueFixedUpdateFunc then executed from there
private static List<System.Action> actionQueuesFixedUpdateFunc = new List<Action>();
//holds Actions copied from actionQueuesFixedUpdateFunc to be executed
List<System.Action> actionCopiedQueueFixedUpdateFunc = new List<System.Action>();
// Used to know if whe have new Action function to execute. This prevents the use of the lock keyword every frame
private volatile static bool noActionQueueToExecuteFixedUpdateFunc = true;
//Used to initialize UnityThread. Call once before any function here
public static void initUnityThread(bool visible = false)
{
if (instance != null)
{
return;
}
if (Application.isPlaying)
{
// add an invisible game object to the scene
GameObject obj = new GameObject("MainThreadExecuter");
if (!visible)
{
obj.hideFlags = HideFlags.HideAndDontSave;
}
DontDestroyOnLoad(obj);
instance = obj.AddComponent<UnityThread>();
}
}
public void Awake()
{
DontDestroyOnLoad(gameObject);
}
//////////////////////////////////////////////COROUTINE IMPL//////////////////////////////////////////////////////
#if (ENABLE_UPDATE_FUNCTION_CALLBACK)
public static void executeCoroutine(IEnumerator action)
{
if (instance != null)
{
executeInUpdate(() => instance.StartCoroutine(action));
}
}
////////////////////////////////////////////UPDATE IMPL////////////////////////////////////////////////////
public static void executeInUpdate(System.Action action)
{
if (action == null)
{
throw new ArgumentNullException("action");
}
lock (actionQueuesUpdateFunc)
{
actionQueuesUpdateFunc.Add(action);
noActionQueueToExecuteUpdateFunc = false;
}
}
public void Update()
{
if (noActionQueueToExecuteUpdateFunc)
{
return;
}
//Clear the old actions from the actionCopiedQueueUpdateFunc queue
actionCopiedQueueUpdateFunc.Clear();
lock (actionQueuesUpdateFunc)
{
//Copy actionQueuesUpdateFunc to the actionCopiedQueueUpdateFunc variable
actionCopiedQueueUpdateFunc.AddRange(actionQueuesUpdateFunc);
//Now clear the actionQueuesUpdateFunc since we've done copying it
actionQueuesUpdateFunc.Clear();
noActionQueueToExecuteUpdateFunc = true;
}
// Loop and execute the functions from the actionCopiedQueueUpdateFunc
for (int i = 0; i < actionCopiedQueueUpdateFunc.Count; i++)
{
actionCopiedQueueUpdateFunc[i].Invoke();
}
}
#endif
////////////////////////////////////////////LATEUPDATE IMPL////////////////////////////////////////////////////
#if (ENABLE_LATEUPDATE_FUNCTION_CALLBACK)
public static void executeInLateUpdate(System.Action action)
{
if (action == null)
{
throw new ArgumentNullException("action");
}
lock (actionQueuesLateUpdateFunc)
{
actionQueuesLateUpdateFunc.Add(action);
noActionQueueToExecuteLateUpdateFunc = false;
}
}
public void LateUpdate()
{
if (noActionQueueToExecuteLateUpdateFunc)
{
return;
}
//Clear the old actions from the actionCopiedQueueLateUpdateFunc queue
actionCopiedQueueLateUpdateFunc.Clear();
lock (actionQueuesLateUpdateFunc)
{
//Copy actionQueuesLateUpdateFunc to the actionCopiedQueueLateUpdateFunc variable
actionCopiedQueueLateUpdateFunc.AddRange(actionQueuesLateUpdateFunc);
//Now clear the actionQueuesLateUpdateFunc since we've done copying it
actionQueuesLateUpdateFunc.Clear();
noActionQueueToExecuteLateUpdateFunc = true;
}
// Loop and execute the functions from the actionCopiedQueueLateUpdateFunc
for (int i = 0; i < actionCopiedQueueLateUpdateFunc.Count; i++)
{
actionCopiedQueueLateUpdateFunc[i].Invoke();
}
}
#endif
////////////////////////////////////////////FIXEDUPDATE IMPL//////////////////////////////////////////////////
#if (ENABLE_FIXEDUPDATE_FUNCTION_CALLBACK)
public static void executeInFixedUpdate(System.Action action)
{
if (action == null)
{
throw new ArgumentNullException("action");
}
lock (actionQueuesFixedUpdateFunc)
{
actionQueuesFixedUpdateFunc.Add(action);
noActionQueueToExecuteFixedUpdateFunc = false;
}
}
public void FixedUpdate()
{
if (noActionQueueToExecuteFixedUpdateFunc)
{
return;
}
//Clear the old actions from the actionCopiedQueueFixedUpdateFunc queue
actionCopiedQueueFixedUpdateFunc.Clear();
lock (actionQueuesFixedUpdateFunc)
{
//Copy actionQueuesFixedUpdateFunc to the actionCopiedQueueFixedUpdateFunc variable
actionCopiedQueueFixedUpdateFunc.AddRange(actionQueuesFixedUpdateFunc);
//Now clear the actionQueuesFixedUpdateFunc since we've done copying it
actionQueuesFixedUpdateFunc.Clear();
noActionQueueToExecuteFixedUpdateFunc = true;
}
// Loop and execute the functions from the actionCopiedQueueFixedUpdateFunc
for (int i = 0; i < actionCopiedQueueFixedUpdateFunc.Count; i++)
{
actionCopiedQueueFixedUpdateFunc[i].Invoke();
}
}
#endif
public void OnDisable()
{
if (instance == this)
{
instance = null;
}
}
}
USAGE:
This implementation allows you to call functions in the 3 most used Unity functions: Update, LateUpdate and FixedUpdate functions. This also allows you call run a coroutine function in the main Thread. It can be extended to be able to call functions in other Unity callback functions such as OnPreRender and OnPostRender.
1.First, initialize it from the Awake() function.
void Awake()
{
UnityThread.initUnityThread();
}
2.To execute a code in the main Thread from another Thread:
UnityThread.executeInUpdate(() =>
{
transform.Rotate(new Vector3(0f, 90f, 0f));
});
This will rotate the current Object the scipt is attached to, to 90 deg. You can now use Unity API(transform.Rotate) in another Thread.
3.To call a function in the main Thread from another Thread:
Action rot = Rotate;
UnityThread.executeInUpdate(rot);
void Rotate()
{
transform.Rotate(new Vector3(0f, 90f, 0f));
}
The #2 and #3 samples executes in the Update function.
4.To execute a code in the LateUpdate function from another Thread:
Example of this is a camera tracking code.
UnityThread.executeInLateUpdate(()=>
{
//Your code camera moving code
});
5.To execute a code in the FixedUpdate function from another Thread:
Example of this when doing physics stuff such as adding force to Rigidbody.
UnityThread.executeInFixedUpdate(()=>
{
//Your code physics code
});
6.To Start a coroutine function in the main Thread from another Thread:
UnityThread.executeCoroutine(myCoroutine());
IEnumerator myCoroutine()
{
Debug.Log("Hello");
yield return new WaitForSeconds(2f);
Debug.Log("Test");
}
Finally, if you don't need to execute anything in the LateUpdate and FixedUpdate functions, you should comment both lines of this code below:
//#define ENABLE_LATEUPDATE_FUNCTION_CALLBACK
//#define ENABLE_FIXEDUPDATE_FUNCTION_CALLBACK
This will increase performance.

I have been using this solution to this problem. Create a script with this code and attach it to a Game Object:
using System;
using System.Collections.Generic;
using System.Collections.Concurrent;
using UnityEngine;
public class ExecuteOnMainThread : MonoBehaviour {
public static readonly ConcurrentQueue<Action> RunOnMainThread = new ConcurrentQueue<Action>();
void Update()
{
if(!RunOnMainThread.IsEmpty)
{
while(RunOnMainThread.TryDequeue(out var action))
{
action?.Invoke();
}
}
}
}
Then when you need to call something on the main thread and access the Unity API from any other function in your application:
ExecuteOnMainThread.RunOnMainThread.Enqueue(() => {
// Code here will be called in the main thread...
});

Much of the writing about threads in Unity is incorrect.
How so?
Unity is, of course, totally frame-based.
When you work in a frame-based system, threading issues are completely different.
Threading issues on a frame-based system are completely different. (In fact, often much easier to deal with.)
Let's say you have a Unity thermometer display that shows some value
Thermo.cs
So it will have a function which is called in Update, like
func void ShowThermoValue(float fraction) {
display code to show the current thermometer value
}
Recall that the "Update" function in Unity simply means "run this once each frame".
That only runs once per frame, and that's that.
(Naturally, it runs only on the "main thread". There's nothing else in Unity! There's just ... "the Unity thread"!)
Somewhere else, perhaps in "IncomingData.cs", you will have a function which handles the concept "a new value has arrived":
[MonoPInvokeCallback(typeof(ipDel))]
public static void NewValueArrives(float f) {
... ???
}
Note that, of course, that is a class function! What else can it be?
You can't "reach in to" a normal Unity function. (Such as ShowThermoValue.) That would be meaningless - it's just a function which runs once each frame.Footnote 1
Let's say: values arrive very frequently and irregularly.
Image you have some sort of scientific devices (perhaps IR thermometers) connected connected to a rack of PCs
Those electronic devices deliver new "temperature" values very often. Let's say dozens of times per frame.
So, "NewValueArrives" is being called 100s of times a second.
So what do you do with the values?
It could not be simpler.
From the arriving-values thread, all you do is ................. wait for it ............. set a variable in the component!!
WTF? All you do is set a variable? That's it? How can it be that simple?
This is one of those unusual situations:
Much of the writing on threads in Unity is, simply, completely hopeless.
Surprisingly, the actual approach is extremely simple.
It's so simple you may think you are doing something wrong!!
So have the variable ...
[System.Nonserialized] public float latestValue;
Set it from the "arriving thread" ...
[MonoPInvokeCallback(typeof(ipDel))]
public static void NewValueArrives(float f) {
ThisScript.runningInstance.latestValue = f; // done
}
Honestly that's it.
Essentially, to be the world's greatest expert at "threading in Unity" - which is, obviously, frame-based - there's nothing more to do than the above.
And whenever ShowThermoValue is called each frame ...................... simply display that value!
Really, that's it!
[System.Nonserialized] public float latestValue;
func void ShowThermoValue() { // note NO arguments here!
display code, draws a thermometer
thermo height = latestValue
}
You're simply displaying the "latest" value.
latestValue may have been set once, twice, ten times, or a hundred times that frame ............ but, you simply display whatever is the value when ShowThermoValue runs that frame!
What else could you display?
The thermometer is updating at 60fps on-screen so you display the latest value. Footnote 2
It's actually that easy. It's just that easy. Surprising but true.
#(Critical aside - don't forget that vector3, etc, are NOT Atomic in Unity/C#)
As user #dymanoid has pointed out (read the important discussion below) it's critical to remember that while float is atomic in the Unity/C# milieu, anything else (say, Vector3 etc) IS NOT ATOMIC. Typically (as in the example here) you only pass floats around from calculations from, say, native plugins, thermometers etc. But it's essential to be aware that vectors and so on are NOT atomic.
Sometimes experienced threading programmers get in a knot with a frame-based system, because: in a frame based system most of the problems caused by racetrack and locking issues ... do not exist conceptually.
In a frame-based system, any game items should simply be displaying or behaving based on some "current value," which is set somewhere. If you have info arriving from other threads, just set those values - you're done.
You can not meaningfully "talk to the main thread" in Unity because that main thread ............. is frame-based!
Most locking, blocking and racetrack issues are non-existent in the frame-based paradigm because: if you set latestValue ten times, a million times, a billion times, in one particular frame .. what can you do? .. you can only display one value during that frame!
Think of an old-fashioned plastic film. You literally just have ...... a frame, and that's it. If you set latestValue a trillion times in one particular frame, ShowThermoValue will simply display (for that 60th of a second) the one value it grabs when it is run.
All you do is: leave information somewhere, which, the frame-paradigm system will utilize during that frame if it wants to.
That's it in a nutshell.
Thus, most "threading issues" disappear in Unity.
All you can do from
other calculation threads or
from plugin threads,
is just "drop-off values" which the game may use.
That's it!
Let's consider the question title...
How do you "... call a function in the main Thread"
This is completely meaningless. The "functions" in Unity are simply functions which the frame engine runs once per frame.
You can't "call" anything in Unity. The frame engine runs a number of things (many things) once per frame.
Note that indeed threads are totally irrelevant. If Unity ran with a billion threads, or with quantum computing, it would have no bearing on anything.
You can't "call a function" in a frame-based system.
Fortunately, the approach to take is dead simple, you just set values, which the frame-based functions can look at when they want! It's really that easy.
Footnotes
1 How could you? As a thought experiment, forget about the issue that you're on a different thread. ShowThermoValue is run once a frame by the frame engine. You can't "call" it in any meaningful way. Unlike in normal OO software, you cannot, say, instantiate an instance of the class (a Component?? meaningless) and run that function - that is completely meaningless.
In "normal" threaded programming, threads can talk back and fore and so on, and in doing so you have concerns about locking, racetrack and so on. But that is all meaningless in an ECS, frame-based, system. There is nothing to "talk to".
Let's say that Unity was in fact multithreaded!!!! So the Unity guys have all of the engine running in a multithreaded manner. It wouldn't make any difference - you can not get "in to" ShowThermoValue in any meaningful way! It's a Component which the frame engine runs once a frame and that's that.
So NewValueArrives is not anywhere - it's a class function!
Let's answer the question in the headline:
"Use Unity API from another Thread or call a function in the main Thread?"
The concept is >> completely meaningless <<. Unity (like all game engines) is frame-based. There's no concept of "calling" a function on the main thread. To make an analogy: it would be like a cinematographer in the celluloid-film era asking how to "move" something actually on one of the frames.
Of course that is meaningless. All you can do is change something for the next photo, the next frame.
2 I refer to the "arriving-values thread" ... in fact! NewValueArrives may, or may not, run on the main thread!!!! It may run on the thread of the plugin, or on some other thread! It may actually be completely single-threaded by the time you deal with the NewValueArrives call! It just doesn't matter! What you do, and all you can do, in a frame-based paradigm, is, "leave laying around" information which Components such as ShowThermoValue, may use, as, they see fit.

Another solution to run code on the main thread, but without requiring a game object and MonoBehavior, is to use SynchronizationContext:
// On main thread, during initialization:
var syncContext = System.Threading.SynchronizationContext.Current;
// On your worker thread
syncContext.Post(_ =>
{
// This code here will run on the main thread
Debug.Log("Hello from main thread!");
}, null);

Use UniRx's multithreading pattern, UniTask and RxSocket together.
[SerializeField] private Text m_Text;
async UniTaskVoid Connect() {
IPEndPoint endPoint = new IPEndPoint(IPAddress.IPv6Loopback, 12345);
// Create a socket client by connecting to the server at the IPEndPoint.
// See the UniRx Async tooling to use await
IRxSocketClient client = await endPoint.ConnectRxSocketClientAsync();
client.ReceiveObservable
.ToStrings()
.ObserveOnMainThread()
.Subscribe(onNext: message =>
{
m_Text.text = message;
}).AddTo(this);
// Send a message to the server.
client.Send("Hello!".ToByteArray());
}

Use Unity API from another Thread or call a function in the main Thread

My problem is I try to use Unity socket to implement something. Each time, when I get a new message I need to update it to the updattext (it is a Unity Text). However, When I do the following code, the void update does not calling every time.
The reason for I do not include updatetext.GetComponent<Text>().text = "From server: "+tempMesg;in the void getInformation is this function is in the thread, when I include that in getInformation() it will come with an error:
getcomponentfastpath can only be called from the main thread
I think the problem is I don't know how to run the main thread and the child thread in C# together? Or there maybe other problems.
Here is my code:
using UnityEngine;
using System.Collections;
using System;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using UnityEngine.UI;
public class Client : MonoBehaviour {
System.Net.Sockets.TcpClient clientSocket = new System.Net.Sockets.TcpClient();
private Thread oThread;
// for UI update
public GameObject updatetext;
String tempMesg = "Waiting...";
// Use this for initialization
void Start () {
updatetext.GetComponent<Text>().text = "Waiting...";
clientSocket.Connect("10.132.198.29", 8888);
oThread = new Thread (new ThreadStart (getInformation));
oThread.Start ();
Debug.Log ("Running the client");
}
// Update is called once per frame
void Update () {
updatetext.GetComponent<Text>().text = "From server: "+tempMesg;
Debug.Log (tempMesg);
}
void getInformation(){
while (true) {
try {
NetworkStream networkStream = clientSocket.GetStream ();
byte[] bytesFrom = new byte[10025];
networkStream.Read (bytesFrom, 0, (int)bytesFrom.Length);
string dataFromClient = System.Text.Encoding.ASCII.GetString (bytesFrom);
dataFromClient = dataFromClient.Substring (0, dataFromClient.IndexOf ("$"));
Debug.Log (" >> Data from Server - " + dataFromClient);
tempMesg = dataFromClient;
string serverResponse = "Last Message from Server" + dataFromClient;
Byte[] sendBytes = Encoding.ASCII.GetBytes (serverResponse);
networkStream.Write (sendBytes, 0, sendBytes.Length);
networkStream.Flush ();
Debug.Log (" >> " + serverResponse);
} catch (Exception ex) {
Debug.Log ("Exception error:" + ex.ToString ());
oThread.Abort ();
oThread.Join ();
}
// Thread.Sleep (500);
}
}
}

Unity is not Thread safe, so they decided to make it impossible to call their API from another Thread by adding a mechanism to throw an exception when its API is used from another Thread.
This question has been asked so many times, but there have been no proper solution/answer to any of them. The answers are usually "use a plugin" or do something not thread-safe. Hopefully, this will be the last one.
The solution you will usually see on Stackoverflow or Unity's forum website is to simply use a boolean variable to let the main thread know that you need to execute code in the main Thread. This is not right as it is not thread-safe and does not give you control to provide which function to call. What if you have multiple Threads that need to notify the main thread?
Another solution you will see is to use a coroutine instead of a Thread. This does not work. Using coroutine for sockets will not change anything. You will still end up with your freezing problems. You must stick with your Thread code or use Async.
One of the proper ways to do this is to create a collection such as List. When you need something to be executed in the main Thread, call a function that stores the code to execute in an Action. Copy that List of Action to a local List of Action then execute the code from the local Action in that List then clear that List. This prevents other Threads from having to wait for it to finish executing.
You also need to add a volatile boolean to notify the Update function that there is code waiting in the List to be executed. When copying the List to a local List, that should be wrapped around the lock keyword to prevent another Thread from writing to it.
A script that performs what I mentioned above:
UnityThread Script:
#define ENABLE_UPDATE_FUNCTION_CALLBACK
#define ENABLE_LATEUPDATE_FUNCTION_CALLBACK
#define ENABLE_FIXEDUPDATE_FUNCTION_CALLBACK
using System;
using System.Collections;
using UnityEngine;
using System.Collections.Generic;
public class UnityThread : MonoBehaviour
{
//our (singleton) instance
private static UnityThread instance = null;
////////////////////////////////////////////////UPDATE IMPL////////////////////////////////////////////////////////
//Holds actions received from another Thread. Will be coped to actionCopiedQueueUpdateFunc then executed from there
private static List<System.Action> actionQueuesUpdateFunc = new List<Action>();
//holds Actions copied from actionQueuesUpdateFunc to be executed
List<System.Action> actionCopiedQueueUpdateFunc = new List<System.Action>();
// Used to know if whe have new Action function to execute. This prevents the use of the lock keyword every frame
private volatile static bool noActionQueueToExecuteUpdateFunc = true;
////////////////////////////////////////////////LATEUPDATE IMPL////////////////////////////////////////////////////////
//Holds actions received from another Thread. Will be coped to actionCopiedQueueLateUpdateFunc then executed from there
private static List<System.Action> actionQueuesLateUpdateFunc = new List<Action>();
//holds Actions copied from actionQueuesLateUpdateFunc to be executed
List<System.Action> actionCopiedQueueLateUpdateFunc = new List<System.Action>();
// Used to know if whe have new Action function to execute. This prevents the use of the lock keyword every frame
private volatile static bool noActionQueueToExecuteLateUpdateFunc = true;
////////////////////////////////////////////////FIXEDUPDATE IMPL////////////////////////////////////////////////////////
//Holds actions received from another Thread. Will be coped to actionCopiedQueueFixedUpdateFunc then executed from there
private static List<System.Action> actionQueuesFixedUpdateFunc = new List<Action>();
//holds Actions copied from actionQueuesFixedUpdateFunc to be executed
List<System.Action> actionCopiedQueueFixedUpdateFunc = new List<System.Action>();
// Used to know if whe have new Action function to execute. This prevents the use of the lock keyword every frame
private volatile static bool noActionQueueToExecuteFixedUpdateFunc = true;
//Used to initialize UnityThread. Call once before any function here
public static void initUnityThread(bool visible = false)
{
if (instance != null)
{
return;
}
if (Application.isPlaying)
{
// add an invisible game object to the scene
GameObject obj = new GameObject("MainThreadExecuter");
if (!visible)
{
obj.hideFlags = HideFlags.HideAndDontSave;
}
DontDestroyOnLoad(obj);
instance = obj.AddComponent<UnityThread>();
}
}
public void Awake()
{
DontDestroyOnLoad(gameObject);
}
//////////////////////////////////////////////COROUTINE IMPL//////////////////////////////////////////////////////
#if (ENABLE_UPDATE_FUNCTION_CALLBACK)
public static void executeCoroutine(IEnumerator action)
{
if (instance != null)
{
executeInUpdate(() => instance.StartCoroutine(action));
}
}
////////////////////////////////////////////UPDATE IMPL////////////////////////////////////////////////////
public static void executeInUpdate(System.Action action)
{
if (action == null)
{
throw new ArgumentNullException("action");
}
lock (actionQueuesUpdateFunc)
{
actionQueuesUpdateFunc.Add(action);
noActionQueueToExecuteUpdateFunc = false;
}
}
public void Update()
{
if (noActionQueueToExecuteUpdateFunc)
{
return;
}
//Clear the old actions from the actionCopiedQueueUpdateFunc queue
actionCopiedQueueUpdateFunc.Clear();
lock (actionQueuesUpdateFunc)
{
//Copy actionQueuesUpdateFunc to the actionCopiedQueueUpdateFunc variable
actionCopiedQueueUpdateFunc.AddRange(actionQueuesUpdateFunc);
//Now clear the actionQueuesUpdateFunc since we've done copying it
actionQueuesUpdateFunc.Clear();
noActionQueueToExecuteUpdateFunc = true;
}
// Loop and execute the functions from the actionCopiedQueueUpdateFunc
for (int i = 0; i < actionCopiedQueueUpdateFunc.Count; i++)
{
actionCopiedQueueUpdateFunc[i].Invoke();
}
}
#endif
////////////////////////////////////////////LATEUPDATE IMPL////////////////////////////////////////////////////
#if (ENABLE_LATEUPDATE_FUNCTION_CALLBACK)
public static void executeInLateUpdate(System.Action action)
{
if (action == null)
{
throw new ArgumentNullException("action");
}
lock (actionQueuesLateUpdateFunc)
{
actionQueuesLateUpdateFunc.Add(action);
noActionQueueToExecuteLateUpdateFunc = false;
}
}
public void LateUpdate()
{
if (noActionQueueToExecuteLateUpdateFunc)
{
return;
}
//Clear the old actions from the actionCopiedQueueLateUpdateFunc queue
actionCopiedQueueLateUpdateFunc.Clear();
lock (actionQueuesLateUpdateFunc)
{
//Copy actionQueuesLateUpdateFunc to the actionCopiedQueueLateUpdateFunc variable
actionCopiedQueueLateUpdateFunc.AddRange(actionQueuesLateUpdateFunc);
//Now clear the actionQueuesLateUpdateFunc since we've done copying it
actionQueuesLateUpdateFunc.Clear();
noActionQueueToExecuteLateUpdateFunc = true;
}
// Loop and execute the functions from the actionCopiedQueueLateUpdateFunc
for (int i = 0; i < actionCopiedQueueLateUpdateFunc.Count; i++)
{
actionCopiedQueueLateUpdateFunc[i].Invoke();
}
}
#endif
////////////////////////////////////////////FIXEDUPDATE IMPL//////////////////////////////////////////////////
#if (ENABLE_FIXEDUPDATE_FUNCTION_CALLBACK)
public static void executeInFixedUpdate(System.Action action)
{
if (action == null)
{
throw new ArgumentNullException("action");
}
lock (actionQueuesFixedUpdateFunc)
{
actionQueuesFixedUpdateFunc.Add(action);
noActionQueueToExecuteFixedUpdateFunc = false;
}
}
public void FixedUpdate()
{
if (noActionQueueToExecuteFixedUpdateFunc)
{
return;
}
//Clear the old actions from the actionCopiedQueueFixedUpdateFunc queue
actionCopiedQueueFixedUpdateFunc.Clear();
lock (actionQueuesFixedUpdateFunc)
{
//Copy actionQueuesFixedUpdateFunc to the actionCopiedQueueFixedUpdateFunc variable
actionCopiedQueueFixedUpdateFunc.AddRange(actionQueuesFixedUpdateFunc);
//Now clear the actionQueuesFixedUpdateFunc since we've done copying it
actionQueuesFixedUpdateFunc.Clear();
noActionQueueToExecuteFixedUpdateFunc = true;
}
// Loop and execute the functions from the actionCopiedQueueFixedUpdateFunc
for (int i = 0; i < actionCopiedQueueFixedUpdateFunc.Count; i++)
{
actionCopiedQueueFixedUpdateFunc[i].Invoke();
}
}
#endif
public void OnDisable()
{
if (instance == this)
{
instance = null;
}
}
}
USAGE:
This implementation allows you to call functions in the 3 most used Unity functions: Update, LateUpdate and FixedUpdate functions. This also allows you call run a coroutine function in the main Thread. It can be extended to be able to call functions in other Unity callback functions such as OnPreRender and OnPostRender.
1.First, initialize it from the Awake() function.
void Awake()
{
UnityThread.initUnityThread();
}
2.To execute a code in the main Thread from another Thread:
UnityThread.executeInUpdate(() =>
{
transform.Rotate(new Vector3(0f, 90f, 0f));
});
This will rotate the current Object the scipt is attached to, to 90 deg. You can now use Unity API(transform.Rotate) in another Thread.
3.To call a function in the main Thread from another Thread:
Action rot = Rotate;
UnityThread.executeInUpdate(rot);
void Rotate()
{
transform.Rotate(new Vector3(0f, 90f, 0f));
}
The #2 and #3 samples executes in the Update function.
4.To execute a code in the LateUpdate function from another Thread:
Example of this is a camera tracking code.
UnityThread.executeInLateUpdate(()=>
{
//Your code camera moving code
});
5.To execute a code in the FixedUpdate function from another Thread:
Example of this when doing physics stuff such as adding force to Rigidbody.
UnityThread.executeInFixedUpdate(()=>
{
//Your code physics code
});
6.To Start a coroutine function in the main Thread from another Thread:
UnityThread.executeCoroutine(myCoroutine());
IEnumerator myCoroutine()
{
Debug.Log("Hello");
yield return new WaitForSeconds(2f);
Debug.Log("Test");
}
Finally, if you don't need to execute anything in the LateUpdate and FixedUpdate functions, you should comment both lines of this code below:
//#define ENABLE_LATEUPDATE_FUNCTION_CALLBACK
//#define ENABLE_FIXEDUPDATE_FUNCTION_CALLBACK
This will increase performance.

I have been using this solution to this problem. Create a script with this code and attach it to a Game Object:
using System;
using System.Collections.Generic;
using System.Collections.Concurrent;
using UnityEngine;
public class ExecuteOnMainThread : MonoBehaviour {
public static readonly ConcurrentQueue<Action> RunOnMainThread = new ConcurrentQueue<Action>();
void Update()
{
if(!RunOnMainThread.IsEmpty)
{
while(RunOnMainThread.TryDequeue(out var action))
{
action?.Invoke();
}
}
}
}
Then when you need to call something on the main thread and access the Unity API from any other function in your application:
ExecuteOnMainThread.RunOnMainThread.Enqueue(() => {
// Code here will be called in the main thread...
});

Much of the writing about threads in Unity is incorrect.
How so?
Unity is, of course, totally frame-based.
When you work in a frame-based system, threading issues are completely different.
Threading issues on a frame-based system are completely different. (In fact, often much easier to deal with.)
Let's say you have a Unity thermometer display that shows some value
Thermo.cs
So it will have a function which is called in Update, like
func void ShowThermoValue(float fraction) {
display code to show the current thermometer value
}
Recall that the "Update" function in Unity simply means "run this once each frame".
That only runs once per frame, and that's that.
(Naturally, it runs only on the "main thread". There's nothing else in Unity! There's just ... "the Unity thread"!)
Somewhere else, perhaps in "IncomingData.cs", you will have a function which handles the concept "a new value has arrived":
[MonoPInvokeCallback(typeof(ipDel))]
public static void NewValueArrives(float f) {
... ???
}
Note that, of course, that is a class function! What else can it be?
You can't "reach in to" a normal Unity function. (Such as ShowThermoValue.) That would be meaningless - it's just a function which runs once each frame.Footnote 1
Let's say: values arrive very frequently and irregularly.
Image you have some sort of scientific devices (perhaps IR thermometers) connected connected to a rack of PCs
Those electronic devices deliver new "temperature" values very often. Let's say dozens of times per frame.
So, "NewValueArrives" is being called 100s of times a second.
So what do you do with the values?
It could not be simpler.
From the arriving-values thread, all you do is ................. wait for it ............. set a variable in the component!!
WTF? All you do is set a variable? That's it? How can it be that simple?
This is one of those unusual situations:
Much of the writing on threads in Unity is, simply, completely hopeless.
Surprisingly, the actual approach is extremely simple.
It's so simple you may think you are doing something wrong!!
So have the variable ...
[System.Nonserialized] public float latestValue;
Set it from the "arriving thread" ...
[MonoPInvokeCallback(typeof(ipDel))]
public static void NewValueArrives(float f) {
ThisScript.runningInstance.latestValue = f; // done
}
Honestly that's it.
Essentially, to be the world's greatest expert at "threading in Unity" - which is, obviously, frame-based - there's nothing more to do than the above.
And whenever ShowThermoValue is called each frame ...................... simply display that value!
Really, that's it!
[System.Nonserialized] public float latestValue;
func void ShowThermoValue() { // note NO arguments here!
display code, draws a thermometer
thermo height = latestValue
}
You're simply displaying the "latest" value.
latestValue may have been set once, twice, ten times, or a hundred times that frame ............ but, you simply display whatever is the value when ShowThermoValue runs that frame!
What else could you display?
The thermometer is updating at 60fps on-screen so you display the latest value. Footnote 2
It's actually that easy. It's just that easy. Surprising but true.
#(Critical aside - don't forget that vector3, etc, are NOT Atomic in Unity/C#)
As user #dymanoid has pointed out (read the important discussion below) it's critical to remember that while float is atomic in the Unity/C# milieu, anything else (say, Vector3 etc) IS NOT ATOMIC. Typically (as in the example here) you only pass floats around from calculations from, say, native plugins, thermometers etc. But it's essential to be aware that vectors and so on are NOT atomic.
Sometimes experienced threading programmers get in a knot with a frame-based system, because: in a frame based system most of the problems caused by racetrack and locking issues ... do not exist conceptually.
In a frame-based system, any game items should simply be displaying or behaving based on some "current value," which is set somewhere. If you have info arriving from other threads, just set those values - you're done.
You can not meaningfully "talk to the main thread" in Unity because that main thread ............. is frame-based!
Most locking, blocking and racetrack issues are non-existent in the frame-based paradigm because: if you set latestValue ten times, a million times, a billion times, in one particular frame .. what can you do? .. you can only display one value during that frame!
Think of an old-fashioned plastic film. You literally just have ...... a frame, and that's it. If you set latestValue a trillion times in one particular frame, ShowThermoValue will simply display (for that 60th of a second) the one value it grabs when it is run.
All you do is: leave information somewhere, which, the frame-paradigm system will utilize during that frame if it wants to.
That's it in a nutshell.
Thus, most "threading issues" disappear in Unity.
All you can do from
other calculation threads or
from plugin threads,
is just "drop-off values" which the game may use.
That's it!
Let's consider the question title...
How do you "... call a function in the main Thread"
This is completely meaningless. The "functions" in Unity are simply functions which the frame engine runs once per frame.
You can't "call" anything in Unity. The frame engine runs a number of things (many things) once per frame.
Note that indeed threads are totally irrelevant. If Unity ran with a billion threads, or with quantum computing, it would have no bearing on anything.
You can't "call a function" in a frame-based system.
Fortunately, the approach to take is dead simple, you just set values, which the frame-based functions can look at when they want! It's really that easy.
Footnotes
1 How could you? As a thought experiment, forget about the issue that you're on a different thread. ShowThermoValue is run once a frame by the frame engine. You can't "call" it in any meaningful way. Unlike in normal OO software, you cannot, say, instantiate an instance of the class (a Component?? meaningless) and run that function - that is completely meaningless.
In "normal" threaded programming, threads can talk back and fore and so on, and in doing so you have concerns about locking, racetrack and so on. But that is all meaningless in an ECS, frame-based, system. There is nothing to "talk to".
Let's say that Unity was in fact multithreaded!!!! So the Unity guys have all of the engine running in a multithreaded manner. It wouldn't make any difference - you can not get "in to" ShowThermoValue in any meaningful way! It's a Component which the frame engine runs once a frame and that's that.
So NewValueArrives is not anywhere - it's a class function!
Let's answer the question in the headline:
"Use Unity API from another Thread or call a function in the main Thread?"
The concept is >> completely meaningless <<. Unity (like all game engines) is frame-based. There's no concept of "calling" a function on the main thread. To make an analogy: it would be like a cinematographer in the celluloid-film era asking how to "move" something actually on one of the frames.
Of course that is meaningless. All you can do is change something for the next photo, the next frame.
2 I refer to the "arriving-values thread" ... in fact! NewValueArrives may, or may not, run on the main thread!!!! It may run on the thread of the plugin, or on some other thread! It may actually be completely single-threaded by the time you deal with the NewValueArrives call! It just doesn't matter! What you do, and all you can do, in a frame-based paradigm, is, "leave laying around" information which Components such as ShowThermoValue, may use, as, they see fit.

Another solution to run code on the main thread, but without requiring a game object and MonoBehavior, is to use SynchronizationContext:
// On main thread, during initialization:
var syncContext = System.Threading.SynchronizationContext.Current;
// On your worker thread
syncContext.Post(_ =>
{
// This code here will run on the main thread
Debug.Log("Hello from main thread!");
}, null);

Use UniRx's multithreading pattern, UniTask and RxSocket together.
[SerializeField] private Text m_Text;
async UniTaskVoid Connect() {
IPEndPoint endPoint = new IPEndPoint(IPAddress.IPv6Loopback, 12345);
// Create a socket client by connecting to the server at the IPEndPoint.
// See the UniRx Async tooling to use await
IRxSocketClient client = await endPoint.ConnectRxSocketClientAsync();
client.ReceiveObservable
.ToStrings()
.ObserveOnMainThread()
.Subscribe(onNext: message =>
{
m_Text.text = message;
}).AddTo(this);
// Send a message to the server.
client.Send("Hello!".ToByteArray());
}