Help with Mutex

[Brian Hampson]

I'm new to getting multi-threading working in C#, so I'm looking for
some help with Mutexes.
I have code that looks like the following:

Mutex MyMutex = new Mutex();

Then later in parts that I want to make sure work at separate times:

void Part1()
{
MyMutex.WaitOne ();
{//Do Stuff}
MyMutex.Release Mutex();
}

void Part2()
{
myTimer.Stop();
MyMutex.WaitOne ();
{//Do other stuff that must be not at the saame time as Part1}
MyMutex.Release Mutex();
myTimer.Start() ;
}

Should this work? Part1 is triggered via a FileSystemWatch er and Part2
is triggered via a timer tick.

[Tom Spink]

Brian Hampson wrote:

I'm new to getting multi-threading working in C#, so I'm looking for
some help with Mutexes.
I have code that looks like the following:

Mutex MyMutex = new Mutex();

Then later in parts that I want to make sure work at separate times:

void Part1()
{
MyMutex.WaitOne ();
{//Do Stuff}
MyMutex.Release Mutex();
}

void Part2()
{
myTimer.Stop();
MyMutex.WaitOne ();
{//Do other stuff that must be not at the saame time as Part1}
MyMutex.Release Mutex();
myTimer.Start() ;
}

Should this work? Part1 is triggered via a FileSystemWatch er and Part2
is triggered via a timer tick.

Hi Brian,

Possibly. But what happens if an error occurs somewhere, and your mutex
isn't released?

The best way, IMHO, to do this would be to use locking:

///
Object lockObject = new Object();

void Part1()
{
lock ( lockObject )
{
// Do Stuff
}
}

void Part2()
{
lock ( lockObject )
{
// Do Other Stuff
}
}
///

--
Hope this helps,
Tom Spink

Google first, ask later.

[Brian Hampson]

Thanks,

I'll give it a try. I'm still not sure why my Mutex code wasn't
working as hoped, I had try/catch/finally inside those mutex locks.
Meh. I'll see about the lock.

Brian Hampson
System Administrator
ALS Laboratory Group, North America

The best way, IMHO, to do this would be to use locking:

///
Object lockObject = new Object();

void Part1()
{
lock ( lockObject )
{
// Do Stuff
}
}

void Part2()
{
lock ( lockObject )
{
// Do Other Stuff
}
}
///

--
Hope this helps,
Tom Spink

Google first, ask later.

[Jon Skeet [C# MVP]]

Brian Hampson <br***********@ gmail.comwrote:

I'm new to getting multi-threading working in C#, so I'm looking for
some help with Mutexes.

I have code that looks like the following:

Code "like" what's pasted is rarely useful - it's easy to miss the bugs
out at the same time as stripping other things (like try/finally).

Could you post a short but complete program which demonstrates the
problem?

See http://www.pobox.com/~skeet/csharp/complete.html for details of
what I mean by that.

(I agree with Brian though - using lock is a lot better.)

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

[Brian Hampson]

Well, I've gone to the lock for now, and when I was stripping all the
comments out of the original function, I found that I had a return that
wouldn't release the mutex in certain circumstances. Doh!

A Homer moment :(

In THEORY, however (if I hadn't had that leaking MUTEX issue)... was my
concept of Mutex implementation sound?

Brian Hampson

Jon wrote:

Brian Hampson <br***********@ gmail.comwrote:

I'm new to getting multi-threading working in C#, so I'm looking for
some help with Mutexes.

I have code that looks like the following:

Code "like" what's pasted is rarely useful - it's easy to miss the bugs
out at the same time as stripping other things (like try/finally).

Could you post a short but complete program which demonstrates the
problem?

See http://www.pobox.com/~skeet/csharp/complete.html for details of
what I mean by that.

(I agree with Brian though - using lock is a lot better.)

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

[Jon Skeet [C# MVP]]

Brian Hampson <br***********@ gmail.comwrote:

Well, I've gone to the lock for now, and when I was stripping all the
comments out of the original function, I found that I had a return that
wouldn't release the mutex in certain circumstances. Doh!

A Homer moment :(

In THEORY, however (if I hadn't had that leaking MUTEX issue)... was my
concept of Mutex implementation sound?

Well, the theory of "wait for the mutex, then release it" is sound - so
long as you don't have multiple mutexes and obtain them in different
orders, etc.

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