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Re: Trouble with mutex/cond destroy on WINCE 3.0

Hi John,

Quite so. The first attempt to detect TryEnterCriticalSection did overlook this, and the additional check was added later. (Eventually Thomas Pfaff's reworking of the mutex routines eliminated the use of critical sections/Win32 mutexes, using the Interlocked routines and semaphores instead.)

However, pthreads-win32 doesn't currently apply the additional check on InterlockedCompareExchange and it hasn't been a problem AFAIK, but there's no reason not to add it as a rule.


Bossom, John wrote:
Hi Ross,

It might not be enough to simply test for the existence of a
function using dynamic loading on win32... Case in point:
Win95 did not support TryEnterCriticalSection at all, whereas
Win98 added the method, but did not implement it (i.e. returned
function not supported if you called it...)

-----Original Message----- From: Ross Johnson [mailto:rpj at ise dot canberra dot edu dot au] Sent: Tuesday, February 25, 2003 6:16 PM To: Craig A. Vanderborgh Cc: pthreads-win32 at sources dot redhat dot com Subject: Re: Trouble with mutex/cond destroy on WINCE 3.0

Craig A. Vanderborgh wrote:

Hello All:

I have just done a port of pthreads-win32 to our recently completed
arm-wince-pe GNU development environment.  This is different that what
others have been doing with pthreads-win32 in the following ways:


It looks like EBUSY is being returned by the call to pthread_mutex_trylock() inside of pthread_mutex_destroy(), so I'm wondering if there's a problem with InterlockedCompareExchange() on arm-wince-pe.

What I think may be happening is this: pthread_win32_process_attach_np() tries to detect if InterlockedCompareExchange() is supported by the system. If this check fails for any reason then: on X86 systems, some X86 specific assembler code is called instead, everywhere it's needed throughout the library via the function pointer ptw32_interlocked_compare_exchange; on non-X86 systems the library implementation of InterlockedCompareExchange (ptw32_InterlockedCompareExchange()) just returns 0, which will result in EBUSY being returned by trylock() [for non recursive mutexes].


What error do you get if you apply pthread_mutex_trylock() to your mutex?
Can you confirm that InterlockedCompareExchange() is supported AND being detected?

BTW, if it turns out that you need an ARM specific InterlockedCompareExchange(), then the following info may be useful:


1. We are not using Visual C++ or EVC.  We have our own port of the GNU
toolchain (binutils-2.13.90 & gcc-3.2).
2. Except for a very few primitives from coredll.dll, we are not using
the Micro$oft runtime - we are using "newlib" instead.

The porting work that was required seemed fairly straightforward and
affected mostly only header files in the end.  Unfortunately, the result
is not entirely working yet.  In particular, mutex/condvar destruction
is always returning "16" instead of "0" (EBUSY??).  Here is an example
program that shows the problem, along with the output:

#include <pthread.h>
#include <errno.h>

main(int argc, char *argv[])
int i, stat;
pthread_mutex_t mutex;
pthread_cond_t cond;

stat = pthread_mutex_init(&mutex, NULL);
printf("pthread_mutex_init returns %d, errno %d\n", stat, errno);

stat = pthread_cond_init(&cond, NULL);
printf("pthread_cond_init returns %d, errno %d\n", stat, errno);

stat = pthread_cond_destroy(&cond);
printf("pthread_cond_destroy returns %d, errno %d\n", stat, errno);

stat = pthread_mutex_destroy(&mutex);
printf("pthread_mutex_destroy returns %d, errno %d\n", stat, errno);


The output is thus:
thread_mutex_init returns 0, errno 0
pthread_cond_init returns 0, errno 0
pthread_cond_destroy returns 16, errno 0
pthread_mutex_destroy returns 16, errno 0

Apparently "EBUSY" is returned when there are waiters on synchronization
objects.  Clearly that can't be the case here so there must be something
wrong with my port.  The question is - what??  Any ideas on where to
look or what to do would be vastly appreciated.

craig vanderborgh
voxware incorporated

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