/* Copyright (C) 2002, 2003 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Ulrich Drepper <drepper@redhat.com>, 2002. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with the GNU C Library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA. */ #include <errno.h> #include <semaphore.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/mman.h> #include <sys/wait.h> int main (void) { size_t ps = sysconf (_SC_PAGESIZE); char tmpfname[] = "/tmp/tst-sem3.XXXXXX"; char data[ps]; void *mem; int fd; sem_t *s; pid_t pid; char *p; fd = mkstemp (tmpfname); if (fd == -1) { printf ("cannot open temporary file: %m\n"); exit (1); } /* Make sure it is always removed. */ unlink (tmpfname); /* Create one page of data. */ memset (data, '\0', ps); /* Write the data to the file. */ if (write (fd, data, ps) != (ssize_t) ps) { puts ("short write"); exit (1); } mem = mmap (NULL, ps, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); if (mem == MAP_FAILED) { printf ("mmap failed: %m\n"); exit (1); } s = (sem_t *) (((uintptr_t) mem + __alignof (sem_t)) & ~(__alignof (sem_t) - 1)); p = (char *) (s + 1); if (sem_init (s, 1, 1) == -1) { puts ("init failed"); exit (1); } if (TEMP_FAILURE_RETRY (sem_wait (s)) == -1) { puts ("1st wait failed"); exit (1); } errno = 0; if (TEMP_FAILURE_RETRY (sem_trywait (s)) != -1) { puts ("trywait succeeded"); exit (1); } else if (errno != EAGAIN) { puts ("trywait didn't return EAGAIN"); exit (1); } *p = 0; puts ("going to fork now"); pid = fork (); if (pid == -1) { puts ("fork failed"); exit (1); } else if (pid == 0) { /* Play some lock ping-pong. It's our turn to unlock first. */ if ((*p)++ != 0) { puts ("child: *p != 0"); exit (1); } if (sem_post (s) == -1) { puts ("child: 1st post failed"); exit (1); } puts ("child done"); } else { if (TEMP_FAILURE_RETRY (sem_wait (s)) == -1) { printf ("parent: 2nd wait failed: %m\n"); exit (1); } if (*p != 1) { puts ("*p != 1"); exit (1); } puts ("parent done"); } exit (0); }