Re: Some tests fail in VC++2005

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

Hi,

Anything you can find out (confirmation it works/doesn't work, or a fix
if necessary) would be very much appreciated.

After I sent my response below I realised my recollection was wrong. The
symptoms are identical to what I found with the Borland build, but the
problem isn't that errno is apparently not thread-safe, but kind of not
dll-safe, if that makes sense. That is, for some reason, the location
that the routines in the dll are using for errno is different to what
the [test] app is using. In the Borland case I confirmed this by
printing the location pointers, and is obviously fixable, but I couldn't
find any information on what might cause the errno() routine to return
different locations for the same thread depending on whether the call
was inside or outside of the dll.

Regards.
Ross

On Fri, 2005-04-22 at 08:34 +0100, Steve Croall wrote:
> If I have time I will download VC++2005 from MSDN and see what the 
> problem is.  If there is one :)
> 
> After using Microsoft's COM+ event system it wouldn't surprise me if 
> there are problems :)
> 
> Steve.
> 
> Ross Johnson wrote:
> > 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
> > 
> > 
> > 
> > 
>