Question

What is it and how to use?

I need that as I have a timer that inserts into DB every second, and I have a shared resource between timer handler and the main thread.
I want to gurantee that if the timer handler takes more than one second in the insertion the waited threads should be executed in order.
This is a sample code for my timer handler:

private void InsertBasicVaraibles(object param)
{
    try
    {
        DataTablesMutex.WaitOne();//mutex for my shared resources
         //insert into DB
    }
    catch (Exception ex)
    {
        //Handle
    }
    finally
    {
        DataTablesMutex.ReleaseMutex();
    }
}

But currently the mutex does not guarantee any order.

Answer 1

You’ll need to write your own class to do this, I found this example (pasted because it looks as though the site’s domain has lapsed):

using System.Threading;

public sealed class QueuedLock
{
    private object innerLock;
    private volatile int ticketsCount = 0;
    private volatile int ticketToRide = 1;

    public QueuedLock()
    {
        innerLock = new Object();
    }

    public void Enter()
    {
        int myTicket = Interlocked.Increment(ref ticketsCount);
        Monitor.Enter(innerLock);
        while (true)
        {

            if (myTicket == ticketToRide)
            {
                return;
            }
            else
            {
                Monitor.Wait(innerLock);
            }
        }
    }

    public void Exit()
    {
        Interlocked.Increment(ref ticketToRide);
        Monitor.PulseAll(innerLock);
        Monitor.Exit(innerLock);
    }
}

Example of usage:

QueuedLock queuedLock = new QueuedLock();

try
{
   queuedLock.Enter();
   // here code which needs to be synchronized
   // in correct order
}
finally
{
    queuedLock.Exit();
}

Source via archive.org