Edit report at https://bugs.php.net/bug.php?id=44109&edit=1
ID: 44109
Comment by: norman dot geist at uni-greifswald dot de
Reported by: thornza at yahoo dot com
Summary: sem_remove does not seem to take SYSVSEM_USAGE into
account
Status: Open
Type: Feature/Change Request
Package: Semaphore related
Operating System: Linux
PHP Version: 5.2.5
Block user comment: N
Private report: N
New Comment:
I just got the same annoying problem as the poster.
I tried to use the semaphores with shared memory to create an openmp like
parallelism to php scripts and apps.
The problem now is, that if I parallelize a for loop with dynamic scheduling
(next free cpu takes next iteration to do) will cause sem_get to run out of
semaphore identifiers for the same semaphore. This maximum number of about
32000 seem not to be adjustable. But I can also not use sem_remove to really
free the sem ids because the other processes can't access the semaphore no more.
Like this, the semaphores seems just unusable (against their original
intention).
Previous Comments:
------------------------------------------------------------------------
[2008-02-13 13:26:54] thornza at yahoo dot com
Description:
------------
Two processes - processA and processB - are using a semaphore.
processA sem_get()s the semaphore. (the semaphore is created)
processB sem_get()s the semaphore. (the semaphore is already created, so the
semaphore id is just returned)
processA sem_acquire()s the semaphore and begins to work in the critical
section.
processB sem_acquire()s the semaphore and BLOCKS.
processA finishes in it's critical section and sem_release()s.
processA sem_remove()s the semaphore ***THE SEMAPHORE HAS NOW BEEN REMOVED -
I think that this part is incorrect****
processB now is NOT able to continue as the semaphore has been removed.
sem_remove() should take the SYSVSEM_USAGE (see sysvsem.c) count into
consideration when it is called. Only if this count is == 1 should the
semaphore be removed. This will allow the last process that is using the
semaphore to remove it from the system.
Reproduce code:
---------------
<?php
//Note - run this script from two different clients at the same time.
//add your own critical section code and output logging.
$semKey = 1234;
$semHandle = sem_get($semKey, 1, 0666, FALSE);
sem_acquire($semHandle);
//critical section
//do something useful here
sem_release($semHandle);
sem_remove($semHandle);
?>
Expected result:
----------------
processA and processB both able to work in their critical sections without
error.
Actual result:
--------------
Log messages such as the following are generated:
[13-Feb-2008 14:36:30] PHP Warning: sem_acquire() [<a
href='function.sem-acquire'>function.sem-acquire</a>]: failed to acquire key
0x2b72: Invalid argument in /opt/MarkDW/Exec/Form.php on line 1282
------------------------------------------------------------------------
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Edit this bug report at https://bugs.php.net/bug.php?id=44109&edit=1
