Develop Reference

How to define a global variable in a busy ASP.NET MVC

In my site, I call a third party API. To avoid hitting its rate limit, I need to define a global variable to enqueue requests. (I'm using RateLimiter any better solution?)
namespace MySite.App_Start
{
public static class Global
{
public static int MaxCount { get; set; } = 30;
public static TimeSpan Interval { get; set; } = TimeSpan.FromSeconds(1);
private static TimeLimiter rateLimiter;
public static TimeLimiter RateLimiter
{
get
{
if (rateLimiter == null)
rateLimiter = TimeLimiter.GetFromMaxCountByInterval(MaxCount, Interval);
return rateLimiter;
}
}
}
}
Then I'll use RateLimiter property. But I've read a lot that having a global variable is not a good idea. Considering my site has a lot of requests per second, is my code safe to use? Thanks.

Your code isn't 100% safe since it could create multiple instances of TimeLimiter in the beginning and depending on surrounding code, it could be a problem. I'm guessing it wouldn't be a big problem, but it's better to write the code properly to begin with.
This is something an IoC container handles nicely, but if you don't want to use one, you could use Lazy:
private static TimeLimiter rateLimiter = new Lazy(() =>
TimeLimiter.GetFromMaxCountByInterval(MaxCount, Interval));
public static TimeLimiter RateLimiter => rateLimiter.Value;

Maybe, you can make it thread-safe by using lock statement.
public static class Global
{
public static int MaxCount { get; set; } = 30;
public static TimeSpan Interval { get; set; } = TimeSpan.FromSeconds(1);
private static object _lockObject = new object();
private static TimeLimiter rateLimiter;
public static TimeLimiter RateLimiter
{
get
{
lock (_lockObject)
{
if (rateLimiter == null)
rateLimiter = TimeLimiter.GetFromMaxCountByInterval(MaxCount, Interval);
return rateLimiter;
}
}
}
}

Your code is not thread-safety.
Try this:
public class Singleton
{
protected Singleton() { }
private sealed class SingletonCreator
{
private static readonly Singleton instance = new Singleton();
public static Singleton Instance { get { return instance; } }
}
public static Singleton Instance
{
get { return SingletonCreator.Instance; }
}
}
Or use your favorite IoC-container with creating SingleInstance object

Why is the GetServer() method returning null?

today I face an issue with some code I have written and really don't know where I have gone wrong, I'll keep it short and sweet basically the GetServer() method in the Faze class is returning null and I am really not sure why, but I was hoping you guys could help me with that.
I have left a few code snippets below of each class involved in the issue and where its initially called to give you a better idea on where things are going wrong.
Program.cs entry point..
static void Main(string[] args)
{
XmlConfigurator.Configure();
Faze.run();
while (true)
Console.ReadKey();
}
Faze class
public static class Faze
{
private static FazeServer fazeServer;
public static void run()
{
Console.Title = "Loading...";
fazeServer = new FazeServer("");
}
public static FazeServer GetServer()
{
return fazeServer;
}
}
FazeServer class
public sealed class FazeServer
{
private ConsoleWorker consoleWorker;
public FazeServer(string lol)
{
LoadServer();
}
private void LoadServer()
{
consoleWorker = new ConsoleWorker();
classLogger.Info("Server has been loaded.");
}
}
ConsoleWorker class
class ConsoleWorker : IDisposable
{
private readonly Timer consoleWorkerTimer;
private readonly int consoleWorkerInterval;
private static ILog classLogger;
public ConsoleWorker()
{
if (Faze.GetServer() == null)
throw new Exception("Server null..");
consoleWorkerInterval = int.Parse(Faze.GetServer().GetConfig().GetConfigElement("console.worker.interval"));
consoleWorkerTimer = new Timer(TimerElapsed, null, TimeSpan.FromMilliseconds(consoleWorkerInterval), TimeSpan.FromMilliseconds(consoleWorkerInterval));
classLogger = LogManager.GetLogger(typeof(ConsoleWorker));
}
private void TimerElapsed(object timerObject)
{
// Do something...
}
public void Dispose()
{
consoleWorkerTimer.Dispose();
}
}
After following the trace, the code that interrupts it is my null check
if (Faze.GetServer() == null)
throw new Exception("Server null..");
Before I added the if statement the line that caused an exception was
consoleWorkerInterval = int.Parse(Faze.GetServer().GetConfig().GetConfigElement("console.worker.interval"));
Why is GetServer() returning null, can anyone help?

I am after a few beers but in the class 'Faze' you have implemented a static field: 'fazeServer' and did not assign a value to it - therefore it is null.
If you would like to assign a value to 'fazeServer' static field please implement in example a static constructor for the class 'Faze' - in example: '
static Faze() { fazeServer = new FazeServer("whatEverString");}'
and that should solve the NRE.
Regards,
P.Sz.

Class fields are initialized to null by default so your code is the equivalent of:
public static class Faze
{
private static FazeServer fazeServer = null;
public static FazeServer GetServer() => fazeServer;
}
of course, calling GetServer() will return the unchaged value which is null.
If you want to initialize it yourself, use a static constructor:
public static class Faze
{
private static FazeServer fazeServer;
static Faze()
{
fazeServer = new FazeServer("");
}
}
or the field initializer:
public static class Faze
{
private static FazeServer fazeServer = new FazeServer("");
}
So it will be certain that you will get an instance when you call GetServer().

You're calling GetServer() before a value has been set in the fazeServer static variable.
The call stack is as follows:
fazeServer = new FazeServer("");
- LoadServer();
- - consoleWorker = new ConsoleWorker();
- - - if (Faze.GetServer() == null)
Or, in plain English:
fazeServer is set to the return value of new FazeServer()
new FazeServer() internally calls LoadServer()
LoadServer() internally calls new ConsoleWorker()
new ConsoleWorker() internally calls Faze.GetServer()
Faze.GetServer() returns the current value of fazeServer
So the code which sets that static variable is internally trying to read that static variable before it has finished setting it.

Singleton with Activator.CreateInstance

I have a class which implements the Singleton design pattern. However, whenever i try to get an instance of that class, using Activator.CreateInstance(MySingletonType) only the private constructor is called. Is there any way to invoke other method than the private constructor?
My class is defined as follow:
public class MySingletonClass{
private static volatile MySingletonClassinstance;
private static object syncRoot = new object();
private MySingletonClass()
{
//activator.createInstance() comes here each intantiation.
}
public static MySingletonClassInstance
{
get
{
if (instance == null)
{
lock (syncRoot)
{
if (instance == null)
instance = new MySingletonClass();
}
}
return instance;
}
}
}
And the instantiation as follow:
Type assemblyType = Type.GetType(realType + ", " + assemblyName);
IService service = Activator.CreateInstance(assemblyType, true) as IService;

Activator.CreateInstance, except for one extreme edge-case, always creates a new instance. I suggest that you probably dont want to use Activator here.
However, if you have no choice, the hacky hack hack hack is to make a class that inherits from ContextBoundObject, and decorate it with a custom subclass of ProxyAttribute. In the custom ProxyAttribute subclass, override CreateInstance to do whatever you want. This is all kinds of evil. But it even works with new Foo().

Hei i do not know why are you creating an object of singleton class using reflection.
the basic purpose of singleton class is that it has only one object and has global access.
however you can access any of your method in singleton class like :
public class MySingletonClass {
private static volatile MySingletonClass instance;
private static object syncRoot = new object();
private MySingletonClass() { }
public static MySingletonClass MySingletonClassInstance {
get {
if (instance == null) {
lock (syncRoot) {
if (instance == null)
instance = new MySingletonClass();
}
}
return instance;
}
}
public void CallMySingleTonClassMethod() { }
}
public class program {
static void Main() {
//calling a
methodMySingletonClass.MySingletonClassInstance
.CallMySingleTonClassMethod();
}
}

Thread safety of C# singleton instance in ApplicationState

I have a bit of code that I've been trying to examine for thread safety. I'm using the basic lazy singleton model found here. I was wondering if it is still thread safe if I'm putting the instance in the HttpApplicationState object. I need to access this instance across all instances of the web application, so if this is not thread safe how can I make it thread safe?
public sealed class EmailWorker {
private HttpApplicationState _app;
private const EMAIL_WORKER = "EmailWorker";
EmailWorker() { }
class NestedWorker {
static NestedWorker() { }
internal static readonly EmailWorker Instance = new EmailWorker();
}
public static void Initialize(HttpApplicationState appState) {
_appState = appState;
_appState.Lock();
if (_appState[EMAIL_WORKER] == null) {
_appState.Add(EMAIL_WORKER, NestedWorker.Instance);
}
_appState.UnLock();
}
public static EmailWorker Instance {
get {
// TODO: If we haven't called Initialize() first then throw exception
return (EmailWorker)_appState[EMAIL_WORKER];
}
}
}

You don't need to use Application state at all.

It should be thread-safe, but why bother?
A "standard" singleton will also be accessible across the entire application, and it won't require injecting and keeping a reference to the HttpApplicationState:
public sealed class EmailWorker
{
private EmailWorker() { }
private static class NestedWorker
{
static NestedWorker() { }
internal static readonly EmailWorker Instance = new EmailWorker();
}
public static EmailWorker Instance
{
get { return NestedWorker.Instance; }
}
}

Is Structuremap singleton thread safe?

Currently I have the following class:
public class PluginManager
{
private static bool s_initialized;
private static object s_lock = new object();
public static void Initialize() {
if (!s_initialized) {
lock (s_lock) {
if (!s_initialized) {
// initialize
s_initialized = true;
}
}
}
}
}
The important thing here is that Initialize() should only be executed once whilst the application is running. I thought that I would refactor this into a singleton class since this would be more thread safe?:
public sealed class PluginService
{
static PluginService() { }
private static PluginService _instance = new PluginService();
public static PluginService Instance { get { return _instance; } }
private bool s_initialized;
public void Initialize() {
if (!s_initialized)
{
// initialize
s_initialized = true;
}
}
}
Question one, is it still necessary to have the lock here (I have removed it) since we will only ever be working on the same instance?
Finally, I want to use DI and structure map to initialize my servcices so I have refactored as below:
public interface IPluginService {
void Initialize();
}
public class NewPluginService : IPluginService
{
private bool s_initialized;
public void Initialize() {
if (!s_initialized) {
// initialize
s_initialized = true;
}
}
}
And in my registry:
ForRequestedType<IPluginService>()
.TheDefaultIsConcreteType<NewPluginService>().AsSingletons();
This works as expected (singleton returning true in the following code):
var instance1 = ObjectFactory.GetInstance<IPluginService>();
var instance2 = ObjectFactory.GetInstance<IPluginService>();
bool singleton = (instance1 == instance2);
So my next question, is the structure map solution as thread safe as the singleton class (second example). The only downside is that this would still allow NewPluginService to be instantiated directly (if not using structure map).
Many thanks,
Ben

I would make several recommendations:
the boolean flag should be volatile
make your singleton instance readonly
the initialization is not thread safe, regardless of the fact that you have only one instance... so it should be synchronized
public sealded class PluginService
{
static PluginService() { }
//make the instance readonly
private static readonly PluginService _instance = new PluginService();
public static PluginService Instance { get { return _instance; } }
// make the flag volatile
private static volatile bool s_initialized = false;
private static object s_lock = new object();
// you still need to synchronize when you're initializing
public void Initialize() {
lock(s_lock)
{
if (!s_initialized)
{
// initialize
s_initialized = true;
}
}
}
}
There is no contention on the structured map, so its thread safety doesn't seem compromised...
The singleton class you had was not thread safe. The main thing to remember is that a single instance does not ensure a single thread can only access it. If there are multiple threads that have a reference to the instance, then there is contention on the instance and the data it's holding. If there is contention then you should ensure thread safety (synchronize at the very minimum).