Subject: possible pthread_mutex_init bug: reads uninitialized memory
From: Frederic Devernay <[email-masked]>
To: [email-masked]
Cc: Olivier Bantiche <[email-masked]>, Frederic Devernay <[email-masked]>
Date: Thu, 30 Aug 2001 09:46:00 +0200

Hello,

there are officially two ways to initialize a pthread mutex:
pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
or
pthread_mutex_t mut;
pthread_mutex_init(&mut,NULL);

the problem is that the pthread_mutex_init in cygwin reads the of-course
uninitialized memory:

as seen in cygwin-1.3.2-1/winsup/cygwin/thread.cc:

__pthread_mutex_init (pthread_mutex_t * mutex,
                      const pthread_mutexattr_t * attr)
{
  if ((((pshared_mutex *)(mutex))->flags & SYS_BASE == SYS_BASE))
    // a pshared mutex
    return EBUSY;
...

If found this bug not by declaring a local variable as above, but by allocating
the mutex. the only workaround I found was to memset the memory area before
calling pthread_mutex_init.

I don't know what a pshared_mutex is, but pthread_mutex_init should really
not assume that anything is valid in the given mutex!

Fred

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