Re: Some tests fail in VC++2005

[Ross Johnson <rpj@callisto.canberra.edu.au>]

On Thu, 2005-04-21 at 16:07 +0200, Uenal Mutlu wrote:
> I've tried the latest 2 pthreads releases with MS compilers.
> VC++6 passes all tests, but VC++2005 fails with about 26 of the
> test programs (tested only in beta 1, beta 2 is out since last monday
> or so but I don't have it yet).
> The first one of the failing test programs is semaphore1.c, line 89:
> 
> nmake clean VC
> ...
> ... Running VC test: mutex1r.exe
> ...... Passed
> cl /D__CLEANUP_C /O2 /Ob0 /W3 /WX /MD /nologo /Yd /Zi -I. semaphore1.c /Fesemaphore1.exe /link /INCREMENTAL:NO pthreadVC2.lib
> ws2_32.lib
> cl : Command line warning D9035 : option 'Yd' has been deprecated and will be removed in a future release
> semaphore1.c
> ... Running VC test: semaphore1.exe
> thread: sem_trywait 1: expected error: No error
> Assertion failed: (errno == EAGAIN), file semaphore1.c, line 89
> NMAKE : fatal error U1077: '.\semaphore1.exe' : return code '0x1'
> Stop.
> NMAKE : fatal error U1077: 'nmake' : return code '0x2'
> Stop.
> 

Strange. It was previously reported that all tests passed with VC++ 2005
beta:
http://sources.redhat.com/ml/pthreads-win32/2005/msg00035.html

Also reported as passing using VC++ 8.0 and VS .NET 2003.

> Below is the function from semaphore1.c where the error occurs.
> It is the line
>      assert(errno == EAGAIN);
> I wonder where errno gets set to this value.
> Is it done in sem_trywait() or maybe in perror()?
> And frankly I don't understand how the below code works at all
> because that branch is entered only if result is -1. The funny
> thing here (for me) is that then the program should stop in the
> previous assert(), but this isn't happening! Then I wonder how
> and why the if condition becomes true...
> 

[See my comments later re perror.]

The test is expecting EAGAIN to be set by sem_trywait(). Since the
semaphore was initialised to 0, sem_trywait should return EAGAIN to
indicate that it would have had to wait.

But the output is saying that after sem_trywait returns -1, errno is 0
('no error'). So it seems as if errno may not be correctly defined in
pthread.h and is conflicting with how it's supposed to work with VC+
+2005 - and is not thread-safe as a result.

Usually errno is defined as:

#define errno *errno()

where errno() is a function that returns a pointer to a thread-specific
errno location.

I don't have access to VC++2005 so won't be able to fix this and test
that it works afterwards. If you (or anyone else can) it would sure
help. I have a similar problem with the Borland and Watcom compilers,
and I just can't figure out what I need to do to fix it.

> void *
> thr(void * arg)
> {
>   sem_t s;
>   int result;
> 
>   assert(sem_init(&s, PTHREAD_PROCESS_PRIVATE, 0) == 0);
> 
>   assert((result = sem_trywait(&s)) == -1);
> 
>   if ( result == -1 )
>   {
>     perror("thread: sem_trywait 1: expected error"); // No error
>     assert(errno == EAGAIN);
>   }
> ...
> 
> I have posted this issue also in
> news://news.microsoft.com/microsoft.public.dotnet.languages.vc
> under the subject "VC++ 2005 beta1 fails with pthreads benchmark tests"
> but the MS guys say the code is broken. Maybe someone could clarify this.
> 

Hmmm, my Googling just now hit on this discussion between UM (you?) and
someone else. Is this the same discussion as the news link you gave:
http://www.codecomments.com/forum292/message465116-2.html

Apart from the unhelpful and highly defensive/diversionary comments from
the other guy about assert abuse etc., I agree that errno should
probably not be read again after the perror call. The standard doesn't
say that perror should preserve errno - only that perror doesn't return
a value and that no errors are defined for it. I'll change the tests.

By the way, here's some code from the MSDN perror web page:
http://msdn.microsoft.com/library/default.asp?url=/library/en-
us/vclib/html/_crt_perror.2c_._wperror.asp

Note that it expects errno to be preserved through the perror() call
too.

// crt_perror.c
/* This program attempts to open a file named
 * NOSUCHF.ILE. Because this file probably doesn't exist,
 * an error message is displayed. The same message is
 * created using perror, strerror, and _strerror.
 */

#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <io.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main( void )
{
   int  fh;

   if( (fh = _open( "NOSUCHF.ILE", _O_RDONLY )) == -1 )
   {
      /* Three ways to create error message: */
      perror( "perror says open failed" );
      printf( "strerror says open failed: %s\n", strerror( errno ) );
      printf( _strerror( "_strerror says open failed" ) );
   }
   else
   {
      printf( "open succeeded on input file\n" );
      _close( fh );
   }
}

Ross