Develop Reference

stopped in the debugger with a C# thread hung on a lock statement, how do I figure out which thread currently owns the lock? [duplicate]

one of the threads in my application blocked at the following lock statement and resulted in a deadlock
void ExecuteCommand()
{
lock(this._lockinstance)
{
// do some operation
}
}
Is it possible to easily identify which thread is currently holding the lock?.. My application has more than 50 threads, which makes it difficult to go through each callstack using visual studio to locate the thread that holds the lock

Some sample code to try out:
class Test {
private object locker = new object();
public void Run() {
lock (locker) { // <== breakpoint here
Console.WriteLine(System.Threading.Thread.CurrentThread.ManagedThreadId);
}
}
}
Set a breakpoint on the indicated line. When it breaks, use Debug + Windows + Memory + Memory 1. Right click the window and choose "4-byte Integer". In the Address box, type &locker. The 2nd word is the thread ID of the thread that owns the lock. Step past the lock statement to see it change.
Beware that the number is the managed thread ID, not the operating system thread ID that you see in the Debug + Windows + Threads window. That kinda sucks, you probably should add some logging to your program that dumps the value of ManagedThreadId so you have a way to match the value to a thread. Update: fixed in later VS versions, the Debug > Windows > Threads debugger window now shows the ManagedThreadId.

Recently I was trying to determine what function was holding a lock and found the following very useful and had not seen in demonstrated anywhere before. I've placed it as an answer here in case others find it useful too.
Many of the other solutions posted earlier require writing a new class and then converting of all lock(blah) to BetterLock(blah) which is a lot of work for debugging and which you may not want in the production/shipped version of your code. Others required having the debugger attached which changes the code's timing and could obscure the issue.
Instead, try the following...
Original code:
object obj = new object();
lock(obj)
{
// Do stuff
}
Modified code for debugging:
object _obj = new object();
object obj
{
get
{
System.Diagnostics.StackFrame frame = new System.Diagnostics.StackFrame(1);
System.Diagnostics.Trace.WriteLine(String.Format("Lock acquired by: {0} on thread {1}", frame.GetMethod().Name, System.Threading.Thread.CurrentThread.ManagedThreadId));
return _obj;
}
}
// Note that the code within lock(obj) and the lock itself remain unchanged.
lock(obj)
{
// Do stuff
}
By exposing obj as a property, at least temporarily, with very minimal code changes you can determine what function acquired the lock last and on what thread - just look at the Trace output for the last entry. Of course you can output any other information you might find useful in the getter as well.
No, this will not let you determine when a lock was released, but if it was getting released in a timely fashion, then you didn't actually have a lock contention issue in the first place.

You can implement a Monitor wrapper that saves stack traces & thread names on enter.
Old way:
private object myLock = new object();
...
lock(myLock)
{
DoSomething();
}
...
With code below:
private SmartLock myLock = new SmartLock();
...
myLock.Lock( () =>
{
DoSomething();
}
);
...
Source:
public class SmartLock
{
private object LockObject = new object();
private string HoldingTrace = "";
private static int WARN_TIMEOUT_MS = 5000; //5 secs
public void Lock(Action action)
{
try
{
Enter();
action.Invoke();
}
catch (Exception ex)
{
Globals.Error("SmartLock Lock action", ex);
}
finally
{
Exit();
}
}
private void Enter()
{
try
{
bool locked = false;
int timeoutMS = 0;
while (!locked)
{
//keep trying to get the lock, and warn if not accessible after timeout
locked = Monitor.TryEnter(LockObject, WARN_TIMEOUT_MS);
if (!locked)
{
timeoutMS += WARN_TIMEOUT_MS;
Globals.Warn("Lock held: " + (timeoutMS / 1000) + " secs by " + HoldingTrace + " requested by " + GetStackTrace());
}
}
//save a stack trace for the code that is holding the lock
HoldingTrace = GetStackTrace();
}
catch (Exception ex)
{
Globals.Error("SmartLock Enter", ex);
}
}
private string GetStackTrace()
{
StackTrace trace = new StackTrace();
string threadID = Thread.CurrentThread.Name ?? "";
return "[" + threadID + "]" + trace.ToString().Replace('\n', '|').Replace("\r", "");
}
private void Exit()
{
try
{
Monitor.Exit(LockObject);
HoldingTrace = "";
}
catch (Exception ex)
{
Globals.Error("SmartLock Exit", ex);
}
}
}

Yes, there is a 'Threads' view that you can use in VS. Break anywhere in your application (or click the 'Break All' button) then you can select each thread and view who has the lock (if anyone).
To add it, go to Debug > Windows > Threads (Ctrl+D,T)

Old posts are old.
But i thought i might give a solution i find to be fairly useful for trying to track down dead locks and other locking problems.
I use a disposable class for my lock - I like Monitor but any locking mechanism could be used.
public class MonitorLock : IDisposable
{
public static MonitorLock CreateLock(object value)
{
return new MonitorLock(value);
}
private readonly object _l;
protected MonitorLock(object l)
{
_l = l;
Console.WriteLine("Lock {0} attempt by {1}", _l, Thread.CurrentThread.ManagedThreadId);
Monitor.Enter(_l);
Console.WriteLine("Lock {0} held by {1}" , _l, Thread.CurrentThread.ManagedThreadId);
}
public void Dispose()
{
Monitor.Exit(_l);
Console.WriteLine("Lock {0} released by {1}", _l, Thread.CurrentThread.ManagedThreadId);
}
}
I use a lock object with a name so I can be clear as to which lock I'm trying to aquire.
public class LockObject
{
public string Name { get; set; }
public LockObject(string name)
{
Name = name;
}
public override string ToString()
{
return Name;
}
}
Finally create a lock object, and then in a using block hold the object.
//create an object to lock on
private readonly object _requestLock = new LockObject("_requestLock");
using (MonitorLock.CreateLock(_requestLock))
{
//do some work
}
Output should be something along the lines of
Lock _requestLock attempt by 92
Lock _requestLock held by 92
Lock _requestLock attempt by 19
Lock _requestLock released by 92
Lock _requestLock held by 19
Lock _requestLock released by 19
Hope that someone finds this useful :)

The Managed Stack Explorer from http://mse.codeplex.com/ or http://www.microsoft.com/downloadS/details.aspx?FamilyID=80cf81f7-d710-47e3-8b95-5a6555a230c2&displaylang=en is excellent in such cases.
It hooks into running managed code (appropriate permissions needed) including live code, and grabs a list of running threads. You can double-click on any of them or (more useful in cases like this) select the lot and hit enter for a quick relatively non-invasive (obviously it's going to consume resources, but it goes in and out as quickly as it can) dump of the current stacks of different threads. Great for finding a deadlock, infinite loop, near-infinite loop (for those times when your application accidentally depends upon astronomers being pessimistic about how long the earth will last to have a hope of completing) and other such cases.

I'm not sure in which version this feature was added, but the Visual Studio 2022 debugger now shows in its Call Stack window the ID of the thread that owns the lock on which another thread is waiting to acquire, e.g.,
I found this over here.

C# Best Practice used for application multithreading log building cross-form instance

I'm building a UI which consists of one main Form with possible instances of additional forms and custom classes. What I'm still missing is a consistent way of logging errors. So what I do is I created try-catch blocks around all code that could generate errors, mainly the things that process incoming data. I'm receiving a constant data flow (JSON) from some site, so the built in threading functionality of the framework makes it a multi threading application. Again, the multi threading part is the built-in functionality, I'm not doing this myself actively, since I'm not that smart yet, from a C# point of view. ;)
For the logging part, I've got the code below from here. Even though I'm not so smart yet, I do think I actually understand what is going on there. My concern/question however, is this: how do I implement a Multi-Threading logging mechanism that writes errors to ONE log file cross-form cross-class.
Here is an example that you can use a reference:
// MyMainForm.cs
namespace MyNameSpace
{
public partial class MyMainForm : Form
{
FooClass MyClass = new FooClass(); //<< errors could occur here
Form f = new MyForm(); //<< errors could occur here
... //<< errors could occur here
}
}
// FooClass.cs
namespace MyNameSpace
{
public class FooClass
{
public string ErrorGeneratingMethod()
{
try...catch(Exception e) { /* Write to Log file */ }
}
}
}
// Don't really know where to put this...
private static ReaderWriterLockSlim _readWriteLock = new ReaderWriterLockSlim();
public void WriteToFileThreadSafe(string text, string context)
{
string t = DateTime.UtcNow.ToString("yyyy-MM-dd HH:mm:ss.fff", CultureInfo.InvariantCulture);
string path = Properties.Settings.Default.FQLogFileLocation;
// Set Status to Locked
_readWriteLock.EnterWriteLock();
try
{
// Append text to the file
using (StreamWriter sw = File.AppendText(path))
{
sw.WriteLine("[" + t + "]["+ context + "]" + text);
sw.Close();
}
} catch (Exception e)
{
MessageBox.Show(e.Message); // Really Exceptional (should never happen)
}
finally
{
// Release lock
_readWriteLock.ExitWriteLock();
}
}
So basically what is important for me to know is where do I put WriteToFileThreadSafe() together with _readWriteLock?
And how do I safely use this function in multiple threads in multiple forms and classes?
Thanks a lot in advance for letting me learn from you guru's :)

C# Enqueue Failure

I have a simple logging mechanism that should be thread safe. It works most of the time, but every now and then I get an exception on this line, "_logQ.Enqueue(s);" that the queue is not long enough. Looking in the debugger there are sometimes just hundreds of items, so I can't see it being resources. The queue is supposed to expand as needed. If I catch the exception as opposed to letting the debugger pause at the exception I see the same error. Is there something not thread safe here? I don't even know how to start debugging this.
static void ProcessLogQ(object state)
{
try
{
while (_logQ.Count > 0)
{
var s = _logQ.Dequeue();
string dir="";
Type t=Type.GetType("Mono.Runtime");
if (t!=null)
{
dir ="/var/log";
}else
{
dir = #"c:\log";
if (!Directory.Exists(dir))
Directory.CreateDirectory(dir);
}
if (Directory.Exists(dir))
{
File.AppendAllText(Path.Combine(dir, "admin.log"), DateTime.Now.ToString("hh:mm:ss ") + s + Environment.NewLine);
}
}
}
catch (Exception)
{
}
finally
{
_isProcessingLogQ = false;
}
}
public static void Log(string s) {
if (_logQ == null)
_logQ = new Queue<string> { };
lock (_logQ)
_logQ.Enqueue(s);
if (!_isProcessingLogQ) {
_isProcessingLogQ = true;
ThreadPool.QueueUserWorkItem(ProcessLogQ);
}
}
Note that the threads all call Log(string s). ProcessLogQ is private to the logger class.
* Edit *
I made a mistake in not mentioning that this is in a .NET 3.5 environment, therefore I can't use Task or ConcurrentQueue. I am working on fixes for the current example within .NET 3.5 constraints.
** Edit *
I believe I have a thread-safe version for .NET 3.5 listed below. I start the logger thread once from a single thread at program start, so there is only one thread running to log to the file (t is a static Thread):
static void ProcessLogQ()
{
while (true) {
try {
lock (_logQ);
while (_logQ.Count > 0) {
var s = _logQ.Dequeue ();
string dir = "../../log";
if (!Directory.Exists (dir))
Directory.CreateDirectory (dir);
if (Directory.Exists (dir)) {
File.AppendAllText (Path.Combine (dir, "s3ol.log"), DateTime.Now.ToString ("hh:mm:ss ") + s + Environment.NewLine);
}
}
} catch (Exception ex) {
Console.WriteLine (ex.Message);
} finally {
}
Thread.Sleep (1000);
}
}
public static void startLogger(){
lock (t) {
if (t.ThreadState != ThreadState.Running)
t.Start ();
}
}
private static void multiThreadLog(string msg){
lock (_logQ)
_logQ.Enqueue(msg);
}

Look at the TaskParallel Library. All the hard work is already done for you. If you're doing this to learn about multithreading read up on locking techniques and pros and cons of each.
Further, you're checking if _logQ is null outside your lock statement, from what I can deduce it's a static field that you're not initializing inside a static constructor. You can avoid doing this null check (which should be inside a lock, it's critical code!) you can ensure thread-safety by making it a static readonly and initializing it inside the static constructor.
Further, you're not properly handling queue states. Since there's no lock during the check of the queue count it could vary on every iteration. You're missing a lock as your dequeuing items.
Excellent resource:
http://www.yoda.arachsys.com/csharp/threads/

For a thread-safe queue, you should use the ConcurrentQueue instead:
https://msdn.microsoft.com/en-us/library/dd267265(v=vs.110).aspx

Error writing to file

The error occurs randomly, my guess is when there is heavy traffic, but i'm having a hard time replicating it. This functionality runs everytime a business transaction is initiated.
Error: System.IO.IOException: The process cannot access the file ''
because it is being used by another process. at
System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
private void writeToTrafficLogFile(string data, string filePath)
{
try
{
StreamWriter logWriter;
if (!File.Exists(filePath))
{
logWriter = new StreamWriter(filePath);
}
else
{
logWriter = File.AppendText(filePath);
}
logWriter.WriteLine(DateTime.Now);
logWriter.WriteLine(data);
logWriter.WriteLine();
logWriter.Close();
}
catch (Exception error) {
sendLoggingErrorEmail(error, "Error Writing writeToTrafficLogFile", "Error Writing writeToTrafficLogFile.\r\n");
}
}
#endregion
}

It might be easier and more bulletproof to switch to an existing, well tested logging solution. Several exist, have a look at dotnetlogging.com where dozens are listed. I can't recommend any, right now I am stuck with log4net but I can't recommend it.

You're probably calling that from multiple threads at the same time...
There are two possible solutions:
A: Create a single thread that writes to the log file from a string that other threads can write to. -- Clarification edit: Have a class with code like
public static List<string> logme = new List<string>();
// Launch LogLoop as a thread!
public static void logloop()
{
while (true)
{
while (logme.Count > 0)
{
File.AppendAllText("log.txt", logme[0] + "\r\n");
logme.RemoveAt(0);
}
Thread.Sleep(500);
}
}
// Oh, and whenever you want to log something, just do:
logme.add("Log this text!");
B: Use a Lock on the log writer.

How to minimize Logging impact

There's already a question about this issue, but it's not telling me what I need to know:
Let's assume I have a web application, and there's a lot of logging on every roundtrip. I don't want to open a debate about why there's so much logging, or how can I do less loggin operations. I want to know what possibilities I have in order to make this logging issue performant and clean.
So far, I've implemented declarative (attribute based) and imperative logging, which seems to be a cool and clean way of doing it... now, what can I do about performance, assuming I can expect those logs to take more time than expected. Is it ok to open a thread and leave that work to it?

Things I would consider:
Use an efficient file format to minimise the quantity of data to be written (e.g. XML and text formats are easy to read but usually terribly inefficient - the same information can be stored in a binary format in a much smaller space). But don't spend lots of CPU time trying to pack data "optimally". Just go for a simple format that is compact but fast to write.
Test use of compression on the logs. This may not be the case with a fast SSD but in most I/O situations the overhead of compressing data is less than the I/O overhead, so compression gives a net gain (although it is a compromise - raising CPU usage to lower I/O usage).
Only log useful information. No matter how important you think everything is, it's likely you can find something to cut out.
Eliminate repeated data. e.g. Are you logging a client's IP address or domain name repeatedly? Can these be reported once for a session and then not repeated? Or can you store them in a map file and use a compact index value whenever you need to reference them? etc
Test whether buffering the logged data in RAM helps improve performance (e.g. writing a thousand 20 byte log records will mean 1,000 function calls and could cause a lot of disk seeking and other write overheads, while writing a single 20,000 byte block in one burst means only one function call and could give significant performance increase and maximise the burst rate you get out to disk). Often writing blocks in sizes like (4k, 16k, 32, 64k) of data works well as it tends to fit the disk and I/O architecture (but check your specific architecture for clues about what sizes might improve efficiency). The down side of a RAM buffer is that if there is a power outage you will lose more data. So you may have to balance performance against robustness.
(Especially if you are buffering...) Dump the information to an in-memory data structure and pass it to another thread to stream it out to disk. This will help stop your primary thread being held up by log I/O. Take care with threads though - for example, you may have to consider how you will deal with times when you are creating data faster than it can be logged for short bursts - do you need to implement a queue, etc?
Are you logging multiple streams? Can these be multiplexed into a single log to possibly reduce disk seeking and the number of open files?
Is there a hardware solution that will give a large bang for your buck? e.g. Have you used SSD or RAID disks? Will dumping the data to a different server help or hinder? It may not always make much sense to spend $10,000 of developer time making something perform better if you can spend $500 to simply upgrade the disk.

I use the code below to Log. It is a singleton that accepts Logging and puts every message into a concurrentqueue. Every two seconds it writes all that has come in to the disk. Your app is now only delayed by the time it takes to put every message in the list. It's my own code, feel free to use it.
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Windows.Forms;
namespace FastLibrary
{
public enum Severity : byte
{
Info = 0,
Error = 1,
Debug = 2
}
public class Log
{
private struct LogMsg
{
public DateTime ReportedOn;
public string Message;
public Severity Seriousness;
}
// Nice and Threadsafe Singleton Instance
private static Log _instance;
public static Log File
{
get { return _instance; }
}
static Log()
{
_instance = new Log();
_instance.Message("Started");
_instance.Start("");
}
~Log()
{
Exit();
}
public static void Exit()
{
if (_instance != null)
{
_instance.Message("Stopped");
_instance.Stop();
_instance = null;
}
}
private ConcurrentQueue<LogMsg> _queue = new ConcurrentQueue<LogMsg>();
private Thread _thread;
private string _logFileName;
private volatile bool _isRunning;
public void Message(string msg)
{
_queue.Enqueue(new LogMsg { ReportedOn = DateTime.Now, Message = msg, Seriousness = Severity.Info });
}
public void Message(DateTime time, string msg)
{
_queue.Enqueue(new LogMsg { ReportedOn = time, Message = msg, Seriousness = Severity.Info });
}
public void Message(Severity seriousness, string msg)
{
_queue.Enqueue(new LogMsg { ReportedOn = DateTime.Now, Message = msg, Seriousness = seriousness });
}
public void Message(DateTime time, Severity seriousness, string msg)
{
_queue.Enqueue(new LogMsg { ReportedOn = time, Message = msg, Seriousness = seriousness });
}
private void Start(string fileName = "", bool oneLogPerProcess = false)
{
_isRunning = true;
// Unique FileName with date in it. And ProcessId so the same process running twice will log to different files
string lp = oneLogPerProcess ? "_" + System.Diagnostics.Process.GetCurrentProcess().Id : "";
_logFileName = fileName == ""
? DateTime.Now.Year.ToString("0000") + DateTime.Now.Month.ToString("00") +
DateTime.Now.Day.ToString("00") + lp + "_" +
System.IO.Path.GetFileNameWithoutExtension(Application.ExecutablePath) + ".log"
: fileName;
_thread = new Thread(LogProcessor);
_thread.IsBackground = true;
_thread.Start();
}
public void Flush()
{
EmptyQueue();
}
private void EmptyQueue()
{
while (_queue.Any())
{
var strList = new List<string>();
//
try
{
// Block concurrent writing to file due to flush commands from other context
lock (_queue)
{
LogMsg l;
while (_queue.TryDequeue(out l)) strList.Add(l.ReportedOn.ToLongTimeString() + "|" + l.Seriousness + "|" + l.Message);
if (strList.Count > 0)
{
System.IO.File.AppendAllLines(_logFileName, strList);
strList.Clear();
}
}
}
catch
{
//ignore errors on errorlogging ;-)
}
}
}
public void LogProcessor()
{
while (_isRunning)
{
EmptyQueue();
// Sleep while running so we write in efficient blocks
if (_isRunning) Thread.Sleep(2000);
else break;
}
}
private void Stop()
{
// This is never called in the singleton.
// But we made it a background thread so all will be killed anyway
_isRunning = false;
if (_thread != null)
{
_thread.Join(5000);
_thread.Abort();
_thread = null;
}
}
}
}

Check if the logger is debug enabled before calling logger.debug, this means your code does not have to evaluate the message string when debug is turned off.
if (_logger.IsDebugEnabled) _logger.Debug($"slow old string {this.foo} {this.bar}");