Is there a “try to lock, skip if timed out” operation in C#?

Question

I need to try to lock on an object, and if its already locked just continue (after time out, or without it).

The C# lock statement is blocking.

Answer 1

Consider using AutoResetEvent and its method WaitOne with a timeout input.

static AutoResetEvent autoEvent = new AutoResetEvent(true);
if(autoEvent.WaitOne(0))
{
    //start critical section
    Console.WriteLine("no other thread here, do your job");
    Thread.Sleep(5000);
    //end critical section
    autoEvent.Set();
}
else
{
    Console.WriteLine("A thread working already at this time.");
}

See https://msdn.microsoft.com/en-us/library/cc189907(v=vs.110).aspx https://msdn.microsoft.com/en-us/library/system.threading.autoresetevent(v=vs.110).aspx and https://msdn.microsoft.com/en-us/library/cc190477(v=vs.110).aspx

Answer 2

I believe that you can use Monitor.TryEnter().

The lock statement just translates to a Monitor.Enter() call and a try catch block.

Answer 3

Ed's got the right function for you. Just don't forget to call Monitor.Exit(). You should use a try-finally block to guarantee proper cleanup.

if (Monitor.TryEnter(someObject))
{
    try
    {
        // use object
    }
    finally
    {
        Monitor.Exit(someObject);
    }
}

Answer 4

I had the same problem, I ended up creating a class TryLock that implements IDisposable and then uses the using statement to control the scope of the lock:

public class TryLock : IDisposable
{
    private object locked;

    public bool HasLock { get; private set; }

    public TryLock(object obj)
    {
        if (Monitor.TryEnter(obj))
        {
            HasLock = true;
            locked = obj;
        }
    }

    public void Dispose()
    {
        if (HasLock)
        {
            Monitor.Exit(locked);
            locked = null;
            HasLock = false;
        }
    }
}

And then use the following syntax to lock:

var obj = new object();

using (var tryLock = new TryLock(obj))
{
    if (tryLock.HasLock)
    {
        Console.WriteLine("Lock acquired..");
    }
}

Answer 5

You'll probably find this out for yourself now that the others have pointed you in the right direction, but TryEnter can also take a timeout parameter.

Jeff Richter's "CLR Via C#" is an excellent book on details of CLR innards if you're getting into more complicated stuff.