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/*
* fork_process.c
* A simple wrapper on top of fork(). This does not handle the
* EXEC_BACKEND case; it might be extended to do so, but it would be
* considerably more complex.
*
* Copyright (c) 1996-2010, PostgreSQL Global Development Group
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/postmaster/fork_process.c,v 1.12 2010/02/26 02:00:55 momjian Exp $
*/
#include "postgres.h"
#include "postmaster/fork_process.h"
#include <fcntl.h>
#include <time.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <unistd.h>
#ifndef WIN32
/*
* Wrapper for fork(). Return values are the same as those for fork():
* -1 if the fork failed, 0 in the child process, and the PID of the
* child in the parent process.
*/
pid_t
fork_process(void)
{
pid_t result;
#ifdef LINUX_PROFILE
struct itimerval prof_itimer;
#endif
/*
* Flush stdio channels just before fork, to avoid double-output problems.
* Ideally we'd use fflush(NULL) here, but there are still a few non-ANSI
* stdio libraries out there (like SunOS 4.1.x) that coredump if we do.
* Presently stdout and stderr are the only stdio output channels used by
* the postmaster, so fflush'ing them should be sufficient.
*/
fflush(stdout);
fflush(stderr);
#ifdef LINUX_PROFILE
/*
* Linux's fork() resets the profiling timer in the child process. If we
* want to profile child processes then we need to save and restore the
* timer setting. This is a waste of time if not profiling, however, so
* only do it if commanded by specific -DLINUX_PROFILE switch.
*/
getitimer(ITIMER_PROF, &prof_itimer);
#endif
result = fork();
if (result == 0)
{
/* fork succeeded, in child */
#ifdef LINUX_PROFILE
setitimer(ITIMER_PROF, &prof_itimer, NULL);
#endif
/*
* By default, Linux tends to kill the postmaster in out-of-memory
* situations, because it blames the postmaster for the sum of child
* process sizes *including shared memory*. (This is unbelievably
* stupid, but the kernel hackers seem uninterested in improving it.)
* Therefore it's often a good idea to protect the postmaster by
* setting its oom_adj value negative (which has to be done in a
* root-owned startup script). If you just do that much, all child
* processes will also be protected against OOM kill, which might not
* be desirable. You can then choose to build with LINUX_OOM_ADJ
* #defined to 0, or some other value that you want child processes to
* adopt here.
*/
#ifdef LINUX_OOM_ADJ
{
/*
* Use open() not stdio, to ensure we control the open flags. Some
* Linux security environments reject anything but O_WRONLY.
*/
int fd = open("/proc/self/oom_adj", O_WRONLY, 0);
/* We ignore all errors */
if (fd >= 0)
{
char buf[16];
snprintf(buf, sizeof(buf), "%d\n", LINUX_OOM_ADJ);
(void) write(fd, buf, strlen(buf));
close(fd);
}
}
#endif /* LINUX_OOM_ADJ */
}
return result;
}
#endif /* ! WIN32 */
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