glibc/manual/examples/ofdlocks.c

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/* Open File Description Locks Usage Example
Copyright (C) 1991-2023 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
Prefer https to http for gnu.org and fsf.org URLs Also, change sources.redhat.com to sourceware.org. This patch was automatically generated by running the following shell script, which uses GNU sed, and which avoids modifying files imported from upstream: sed -ri ' s,(http|ftp)(://(.*\.)?(gnu|fsf|sourceware)\.org($|[^.]|\.[^a-z])),https\2,g s,(http|ftp)(://(.*\.)?)sources\.redhat\.com($|[^.]|\.[^a-z]),https\2sourceware.org\4,g ' \ $(find $(git ls-files) -prune -type f \ ! -name '*.po' \ ! -name 'ChangeLog*' \ ! -path COPYING ! -path COPYING.LIB \ ! -path manual/fdl-1.3.texi ! -path manual/lgpl-2.1.texi \ ! -path manual/texinfo.tex ! -path scripts/config.guess \ ! -path scripts/config.sub ! -path scripts/install-sh \ ! -path scripts/mkinstalldirs ! -path scripts/move-if-change \ ! -path INSTALL ! -path locale/programs/charmap-kw.h \ ! -path po/libc.pot ! -path sysdeps/gnu/errlist.c \ ! '(' -name configure \ -execdir test -f configure.ac -o -f configure.in ';' ')' \ ! '(' -name preconfigure \ -execdir test -f preconfigure.ac ';' ')' \ -print) and then by running 'make dist-prepare' to regenerate files built from the altered files, and then executing the following to cleanup: chmod a+x sysdeps/unix/sysv/linux/riscv/configure # Omit irrelevant whitespace and comment-only changes, # perhaps from a slightly-different Autoconf version. git checkout -f \ sysdeps/csky/configure \ sysdeps/hppa/configure \ sysdeps/riscv/configure \ sysdeps/unix/sysv/linux/csky/configure # Omit changes that caused a pre-commit check to fail like this: # remote: *** error: sysdeps/powerpc/powerpc64/ppc-mcount.S: trailing lines git checkout -f \ sysdeps/powerpc/powerpc64/ppc-mcount.S \ sysdeps/unix/sysv/linux/s390/s390-64/syscall.S # Omit change that caused a pre-commit check to fail like this: # remote: *** error: sysdeps/sparc/sparc64/multiarch/memcpy-ultra3.S: last line does not end in newline git checkout -f sysdeps/sparc/sparc64/multiarch/memcpy-ultra3.S
2019-09-07 13:40:42 +08:00
along with this program; if not, see <https://www.gnu.org/licenses/>.
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <pthread.h>
#define FILENAME "/tmp/foo"
#define NUM_THREADS 3
#define ITERATIONS 5
void *
thread_start (void *arg)
{
int i, fd, len;
long tid = (long) arg;
char buf[256];
struct flock lck = {
.l_whence = SEEK_SET,
.l_start = 0,
.l_len = 1,
};
fd = open ("/tmp/foo", O_RDWR | O_CREAT, 0666);
for (i = 0; i < ITERATIONS; i++)
{
lck.l_type = F_WRLCK;
fcntl (fd, F_OFD_SETLKW, &lck);
len = sprintf (buf, "%d: tid=%ld fd=%d\n", i, tid, fd);
lseek (fd, 0, SEEK_END);
write (fd, buf, len);
fsync (fd);
lck.l_type = F_UNLCK;
fcntl (fd, F_OFD_SETLK, &lck);
/* sleep to ensure lock is yielded to another thread */
usleep (1);
}
pthread_exit (NULL);
}
int
main (int argc, char **argv)
{
long i;
pthread_t threads[NUM_THREADS];
truncate (FILENAME, 0);
for (i = 0; i < NUM_THREADS; i++)
pthread_create (&threads[i], NULL, thread_start, (void *) i);
pthread_exit (NULL);
return 0;
}