Why is this program in error? `Object synchronization method was called from an unsynchronized block of code`

Question

What is wrong with this code? i get a 'Object synchronization method was called from an unsynchronized block of code'. I found one result on google that said i may be releasing a mutex before locking but according to my output this is not the case. Here is the mutex code without the other code in between.

-edit- sorry guys, wrong paste.

My output

1W
1W
2W

code

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;

namespace sqliteTest
{
    class Program
    {
        static volatile Mutex mut1 = new Mutex();
        static volatile Mutex mut2 = new Mutex();
        static void Main(string[] args)
        {
            mut1.WaitOne(); Console.WriteLine("1W");
            Thread oThread = new Thread(new ThreadStart(fn2));
            oThread.Start();
            mut1.WaitOne(); Console.WriteLine("1W");
            update(0);
        }
        static void fn2()
        {
            mut2.WaitOne(); Console.WriteLine("2W");
            mut1.ReleaseMutex(); Console.WriteLine("1R");
            mut2.WaitOne(); Console.WriteLine("2W");
            update(1);
            mut1.ReleaseMutex(); Console.WriteLine("1R");
        }
        static void update(int t)
        {
            mut2.ReleaseMutex(); Console.WriteLine("2R");
            if (t == 0)
            {
                mut1.WaitOne();
                Console.WriteLine("1W");
            }
        }
    }
}

Either line 37 or 49. Those are where both threads are in my debugger. — user34537
oops. +1 dtb. In the newly pasted code it happens at 23 and 30 — user34537

Hans Passant Hans Passant · Accepted Answer · 2009-12-12T22:42:23

It is not a great error message, Windows produces it. What it really means is that you are calling ReleaseMutex on a mutex that you don't own. You'll get past the first exception with

static volatile Mutex mut2 = new Mutex(true);

But then it will die inside the thread when it calls ReleaseMutex on mut1, which it doesn't own. Not sure what you're trying to do, the code doesn't make much sense to me.

Why is this program in error? `Object synchronization method was called from an unsynchronized block of code`

4 Answers