[Fwd: apr/win32 misinterpreted the meaning of WAIT_ABANDONED]

[Kiyo Kelvin Lee <ki...@taskic.com>]

-------- Original Message --------
Subject: apr/win32 misinterpreted the meaning of WAIT_ABANDONED
Date: Mon, 31 Oct 2005 17:54:32 +1100
From: Kiyo Kelvin Lee <ki...@hotmail.com>
Newsgroups: gmane.comp.apache.apr.devel

I am a bit surprised to find that APR interpreted WAIT_ABANDONED as
equivalent to WAIT_OBJECT_0. See apr_proc_mutex_lock() and
apr_proc_mutex_trylock().
I believe this is wrong. According to doco from MS, WAIT_ABANDONED only
means the ownership of the mutex has been changed. The mutex is remain
**non-signaled** (or becomes so if it was signaled), i.e. while one
thread get the return code WAIT_ABANDONED, it is possible that another
thread would get the mutex signaled instead. So we can't simple return
APR_SUCCESS as described in this notes in the CHANGES file:

   *) Win32: apr_proc_mutex_trylock and apr_proc_mutex_lock were
      incorrectly returning APR_BUSY if the lock was previously
      held by a thread that exited before releasing the lock
      (ie, if the process holding the lock segfaults). The MSDN
      doc says when WaitForSingleObject returns WAIT_ABANDONED,
      the calling thread takes ownership of the mutex, so these
      two routines should return APR_SUCCESS in this case, not
      APR_BUSY. [Bill Stoddard]

However, we shouldn't return APR_BUSY either.

The normal proper way to handle WAIT_ABANDONED is to put the
WaitForSingleObject() (or any other equivalent API) in a loop, e.g.:

	do {
		rc = WaitForSingleObject(mutex, INFINITE);
	} while (rc == WAIT_ABANDONED);

Regards,
Kiyo

Re: [Fwd: apr/win32 misinterpreted the meaning of WAIT_ABANDONED]

[Bill Stoddard <bi...@wstoddard.com>]

Kiyo Kelvin Lee wrote:
> 
> 
> -------- Original Message --------
> Subject: apr/win32 misinterpreted the meaning of WAIT_ABANDONED
> Date: Mon, 31 Oct 2005 17:54:32 +1100
> From: Kiyo Kelvin Lee <ki...@hotmail.com>
> Newsgroups: gmane.comp.apache.apr.devel
> 
> I am a bit surprised to find that APR interpreted WAIT_ABANDONED as
> equivalent to WAIT_OBJECT_0. See apr_proc_mutex_lock() and
> apr_proc_mutex_trylock().
> I believe this is wrong. According to doco from MS, WAIT_ABANDONED only
> means the ownership of the mutex has been changed. The mutex is remain
> **non-signaled** (or becomes so if it was signaled), i.e. while one
> thread get the return code WAIT_ABANDONED, it is possible that another
> thread would get the mutex signaled instead. So we can't simple return
> APR_SUCCESS as described in this notes in the CHANGES file:
> 
>   *) Win32: apr_proc_mutex_trylock and apr_proc_mutex_lock were
>      incorrectly returning APR_BUSY if the lock was previously
>      held by a thread that exited before releasing the lock
>      (ie, if the process holding the lock segfaults). The MSDN
>      doc says when WaitForSingleObject returns WAIT_ABANDONED,
>      the calling thread takes ownership of the mutex, so these
>      two routines should return APR_SUCCESS in this case, not
>      APR_BUSY. [Bill Stoddard]
> 
> However, we shouldn't return APR_BUSY either.
> 
> The normal proper way to handle WAIT_ABANDONED is to put the
> WaitForSingleObject() (or any other equivalent API) in a loop, e.g.:
> 
>     do {
>         rc = WaitForSingleObject(mutex, INFINITE);
>     } while (rc == WAIT_ABANDONED);
> 
> Regards,
> Kiyo

Kiyo,
Your explanation sounds right to me. Submit a patch.

Bill