Re: thread_test.c problems

wespvp@syntegra.com wrote:
> On 4/4/04 12:33 AM, "joseph speigle" <joe.speigle@jklh.us> wrote:
>
> > have you tried adding a volatile keyword to the
> >
> > int volatile errno1_set = 0;
> > int volatile errno2_set = 0;
> >
> > that should stop while-loop optimizing for cases where the variable is
> > modified in a scope the compiler would be ignorant of, and precludes compiler
> > while-loop optimization.  That would then tell you if it was a while loop
> > optimization problem.
>
> That cures the problem on all systems.  What needs to be done to get this
> updated in the tip?
>
> > As for me on RH 8.0
> >
> > gcc -v
> > Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/3.2/specs
> > Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
> > --infodir=/usr/share/info --enable-shared --enable-threads=posix
> > --disable-checking --host=i386-redhat-linux --with-system-zlib
> > --enable-__cxa_atexit
> > Thread model: posix
> > gcc version 3.2 20020903 (Red Hat Linux 8.0 3.2-7)
> >
> > sorry, they all run yes/no/no
>
> I don't know what is different, but I've tried it on RH 7.2, RH AS 3.0, and
> Mac OS X.  All hang in an infinite loop with the tip version of
> thread_test.c, and all work if I add 'volatile' to the definitions of
> errno1_set and errno2_set.
>
> There's still the question of which version of the program is giving the
> right answers - the 7.4.2 version or the tip version?

I have applied the following patch to CVS head which does a getpid() in
the loop, rather than nothing.  getpid() should force a system call,
which will make it more likely for the other thread to get CPU time and
complete its tests.

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073
Index: thread_test.c
===================================================================
RCS file: /cvsroot/pgsql-server/src/tools/thread/thread_test.c,v
retrieving revision 1.9
retrieving revision 1.10
diff -c -c -r1.9 -r1.10
*** thread_test.c    28 Mar 2004 02:37:31 -0000    1.9
--- thread_test.c    4 Apr 2004 17:23:54 -0000    1.10
***************
*** 105,111 ****
      /* wait for other thread to set errno */
      errno1_set = 1;
      while (errno2_set == 0)
!         /* loop */;
      if (errno != EEXIST)
      {
              fprintf(stderr, "errno not thread-safe; exiting\n");
--- 105,111 ----
      /* wait for other thread to set errno */
      errno1_set = 1;
      while (errno2_set == 0)
!         getpid();    /* force system call */
      if (errno != EEXIST)
      {
              fprintf(stderr, "errno not thread-safe; exiting\n");
***************
*** 128,135 ****
          passwd_p1 = NULL;    /* force thread-safe failure report */
      }

!     hostent_p1 = gethostbyname("yahoo.com");
!     p = gethostbyname("slashdot.org");
      if (hostent_p1 != p)
      {
          printf("Your gethostbyname() changes the static memory area between calls\n");
--- 128,135 ----
          passwd_p1 = NULL;    /* force thread-safe failure report */
      }

!     hostent_p1 = gethostbyname("www.yahoo.com");
!     p = gethostbyname("www.weather.com");
      if (hostent_p1 != p)
      {
          printf("Your gethostbyname() changes the static memory area between calls\n");
***************
*** 151,157 ****
      /* wait for other thread to set errno */
      errno2_set = 1;
      while (errno1_set == 0)
!         /* loop */;
      if (errno != ENOENT)
      {
              fprintf(stderr, "errno not thread-safe; exiting\n");
--- 151,157 ----
      /* wait for other thread to set errno */
      errno2_set = 1;
      while (errno1_set == 0)
!         getpid();    /* force system call */
      if (errno != ENOENT)
      {
              fprintf(stderr, "errno not thread-safe; exiting\n");
***************
*** 174,181 ****
          passwd_p2 = NULL;    /* force thread-safe failure report */
      }

!     hostent_p2 = gethostbyname("google.com");
!     p = gethostbyname("postgresql.org");
      if (hostent_p2 != p)
      {
          printf("Your gethostbyname() changes the static memory area between calls\n");
--- 174,181 ----
          passwd_p2 = NULL;    /* force thread-safe failure report */
      }

!     hostent_p2 = gethostbyname("www.google.com");
!     p = gethostbyname("www.postgresql.org");
      if (hostent_p2 != p)
      {
          printf("Your gethostbyname() changes the static memory area between calls\n");