Refactor fork()-related code. We need to do various housekeeping tasks

before we can invoke fork() -- flush stdio buffers, save and restore the
profiling timer on Linux with LINUX_PROFILE, and handle BeOS stuff. This
patch moves that code into a single function, fork_process(), instead of
duplicating it at the various callsites of fork().

This patch doesn't address the EXEC_BACKEND case; there is room for
further cleanup there.

src/backend/postmaster/fork_process.c

@@ -0,0 +1,80 @@
+/*
+ * 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) 1996-2005, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/fork_process.c,v 1.1 2005/03/10 07:14:03 neilc Exp $
+ */
+#include "postgres.h"
+#include "postmaster/fork_process.h"
+
+#include <unistd.h>
+
+/*
+ * 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
+
+#ifdef __BEOS__
+	/* Specific beos actions before backend startup */
+	beos_before_backend_startup();
+#endif
+
+	result = fork();
+	if (result == (pid_t) -1)
+	{
+		/* fork failed */
+#ifdef __BEOS__
+		/* Specific beos backend startup actions */
+		beos_backend_startup_failed();
+#endif
+	}
+	else if (result == 0)
+	{
+		/* fork succeeded, in child */
+#ifdef LINUX_PROFILE
+		setitimer(ITIMER_PROF, &prof_itimer, NULL);
+#endif
+
+#ifdef __BEOS__
+		/* Specific beos backend startup actions */
+		beos_backend_startup();
+#endif
+	}
+
+	return result;
+}