Hi,

I'm trying to syncronize access to a shared resource between processes
using system semaphores.

The processes are spawned by Cruise Control.Net.  I use
OpenExisting,and if that fails I catch the exception and use new
Semaphore( name );

The problem is that OpenExisting always fails, even though the other
process has created the semaphore.

The CCNET service is running as a domain user.

Any ideas?

Thanks
Andy

Do you want mutually exclusive access?

I think Mutex would be a better option...

Nnot sure about how you have created the first semaphore.. does the original
thread has the ownership during creation?
What is the count?
What is the upper limit?

Gaurav,

Yes, I wanted mutally exclusive access.  However, no matter what I did,
the second process would throw an AbandonedMutexException when it
returned from WaitOne.

I think I did figure this out though; I now have a static variable to
hold onto the semaphore after the first nant task I wrote completes.
Then the second one attempts to access that static variable.  This
seems to keep the semaphore from being GCed under a CCNET environment.

Don't know why it worked as my user and not under CCNET, but keeping a
reference to the semaphore makes it work under CCNET as well.  FWIW, I
did try this same static refrence trick with the Mutex, but it always
resulted in an AbandonedMutexException.

Andy

Gaurav Vaish (www.EdujiniOnline.com) wrote:
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Oh, to answer your questions..

Initial count was 1, max count was one.  I didn't see anyway to owner
ship of a semaphor, I don't think it supports that concept.

In my aquireLock i used new Semaphore( 1, 1, LockName );

In my releaseLock I used OpenExisting..

Andy

Gaurav Vaish (www.EdujiniOnline.com) wrote:
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My fault... ownership is in the case of Mutex.. :D

Regarding your case... not sure but I think you earlier had a, probably,
local variable or a instance-field that got garbage-collected somewhere down
the line and hence, Semaphore being abandoned.

Semaphores don't seem to care about being abandoned.  Did you mean
Mutex?

I'm not sure that was the problem either, because I held a static
reference to the mutex so that a single nant process didn't lose the
reference until the AppDomain ended..

Releasing the mutex woudl work find as it would use that static
reference, but the other process still threw the exception.  Oh well,
it works now, that's all I care about.

Andy

Hmm... all's well that ends well.
Probably, I'll put this "interesting" study in my blog.

Let me also try to reproduce it here... :)

Well to accurately repo this, you'll have to create a pair of Nant
tasks.. one to get the Mutex and one to release it.  The idea is that
in your build file you get the lock, do some stuff, then release the
lock.

The AbandonedMutexException  would show up just opening a couple of
console windows and running the same test build (which had a sleep
between getting and releasing the lock).

HTH
Andy

Gaurav Vaish (www.EdujiniOnline.com) wrote:
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Well to accurately repo this, you'll have to create a pair of Nant
tasks.. one to get the Mutex and one to release it.  The idea is that
in your build file you get the lock, do some stuff, then release the
lock.  Oh, the tasks also took a lockName which was used to globally
name the mutex.

The AbandonedMutexException  would show up just opening a couple of
console windows and running the same test build (which had a sleep
between getting and releasing the lock).

HTH
Andy

Gaurav Vaish (www.EdujiniOnline.com) wrote:
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Hi Andy,

Thanks for the input.

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