Can two threads execute in the same lock region concurrently?

Russell Stuart

I always believed .Net monitors were a superset of the Java
synchronization mechanisms. The code below produces both
"Thread 1" and "Thread 2" lines, implying that two threads
are both executing in locked region guarded by the same
monitor. I thought that wasn't supposed to happen. Am I
wrong? It was compiled and run under VS 2003.

If you run it under the debugger then the behaviour changes -
only "Thread 1" lines are produced. This is what I expected
to happen in all cases.

using System;
using System.Threading;

public class Test {
Thread t1, t2;

public void Run1() {
Thread.Sleep(1000);
lock (this) {
Monitor.Pulse(this);
t2.Interrupt();
for (;;)
Console.WriteLine("Thread 1");
}
}

public void Run2() {
lock (this) {
try {
Monitor.Wait(this);
}
catch (ThreadInterruptedException) {
Console.WriteLine("2 Interrupted");
}
for (;;)
Console.WriteLine("Thread 2");
}
}

public void Go() {
t1 = new Thread(new ThreadStart(Run1));
t2 = new Thread(new ThreadStart(Run2));
t1.Start();
t2.Start();
}

public static void Main() {
new Test().Go();
}
}

Nov 22 '05 #1

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Jon Skeet [C# MVP]

Russell Stuart <ru**********@stuart.id.au> wrote:

I always believed .Net monitors were a superset of the Java
synchronization mechanisms. The code below produces both
"Thread 1" and "Thread 2" lines, implying that two threads
are both executing in locked region guarded by the same
monitor. I thought that wasn't supposed to happen. Am I
wrong? It was compiled and run under VS 2003.

Please see my reply in the C# newsgroup - there's no need to multipost.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

Nov 22 '05 #2

Jon Skeet [C# MVP]

Jon Skeet [C# MVP] <sk***@pobox.com> wrote:

Russell Stuart <ru**********@stuart.id.au> wrote:
I always believed .Net monitors were a superset of the Java
synchronization mechanisms. The code below produces both
"Thread 1" and "Thread 2" lines, implying that two threads
are both executing in locked region guarded by the same
monitor. I thought that wasn't supposed to happen. Am I
wrong? It was compiled and run under VS 2003.

Please see my reply in the C# newsgroup - there's no need to multipost.

Sorry, of course it wasn't in the C# newsgroup. It was in this
newsgroup. So why the repeat post?

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

Nov 22 '05 #3

Russell Stuart

On Thu, 06 May 2004 08:33:10 +0100, Jon Skeet[ C# MVP] wrote:

Sorry, of course it wasn't in the C# newsgroup. It was in this
newsgroup. So why the repeat post?

Becuase I originally posted the query last night on 247. When
I came in this morning I couldn't see it - so I posted it
using a normal nntp client.

Then both posts appeared. Sorry for the confusion.

Nov 22 '05 #4

Jon Skeet [C# MVP]

Russell Stuart <ru**********@stuart.id.au> wrote:

On Thu, 06 May 2004 08:33:10 +0100, Jon Skeet[ C# MVP] wrote:
Sorry, of course it wasn't in the C# newsgroup. It was in this
newsgroup. So why the repeat post?

Becuase I originally posted the query last night on 247. When
I came in this morning I couldn't see it - so I posted it
using a normal nntp client.

Then both posts appeared. Sorry for the confusion.

Fair enough :)

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

Nov 22 '05 #5

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