Partially deduplicate interrupt handling for background processes.

Where possible, share signal handler code and main loop interrupt
checking. This saves quite a bit of code and should simplify
maintenance, too.

This commit intends not to change the way anything works, even
though that might allow more code to be unified. It does unify
a bunch of individual variables into a ShutdownRequestPending
flag that has is now used by a bunch of different process types,
though.

Patch by me, reviewed by Andres Freund and Daniel Gustafsson.

Discussion: http://postgr.es/m/CA+TgmoZwDk=BguVDVa+qdA6SBKef=PKbaKDQALTC_9qoz1mJqg@mail.gmail.com

1 files changed, 108 insertions, 0 deletions

diff --git a/src/backend/postmaster/interrupt.c b/src/backend/postmaster/interrupt.c
new file mode 100644
index 00000000000..6900cd02f6f
--- /dev/null
+++ b/src/backend/postmaster/interrupt.c
@@ -0,0 +1,108 @@
+/*-------------------------------------------------------------------------
+ *
+ * interrupt.c
+ *	  Interrupt handling routines.
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/postmaster/interrupt.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <unistd.h>
+
+#include "miscadmin.h"
+#include "postmaster/interrupt.h"
+#include "storage/ipc.h"
+#include "storage/latch.h"
+#include "utils/guc.h"
+
+volatile sig_atomic_t ConfigReloadPending = false;
+volatile sig_atomic_t ShutdownRequestPending = false;
+
+/*
+ * Simple interrupt handler for main loops of background processes.
+ */
+void
+HandleMainLoopInterrupts(void)
+{
+	if (ConfigReloadPending)
+	{
+		ConfigReloadPending = false;
+		ProcessConfigFile(PGC_SIGHUP);
+	}
+
+	if (ShutdownRequestPending)
+		proc_exit(0);
+}
+
+/*
+ * Simple signal handler for triggering a configuration reload.
+ *
+ * Normally, this handler would be used for SIGHUP. The idea is that code
+ * which uses it would arrange to check the ConfigReloadPending flag at
+ * convenient places inside main loops, or else call HandleMainLoopInterrupts.
+ */
+void
+SignalHandlerForConfigReload(SIGNAL_ARGS)
+{
+	int			save_errno = errno;
+
+	ConfigReloadPending = true;
+	SetLatch(MyLatch);
+
+	errno = save_errno;
+}
+
+/*
+ * Simple signal handler for exiting quickly as if due to a crash.
+ *
+ * Normally, this would be used for handling SIGQUIT.
+ */
+void
+SignalHandlerForCrashExit(SIGNAL_ARGS)
+{
+	/*
+	 * We DO NOT want to run proc_exit() or atexit() callbacks -- we're here
+	 * because shared memory may be corrupted, so we don't want to try to
+	 * clean up our transaction.  Just nail the windows shut and get out of
+	 * town.  The callbacks wouldn't be safe to run from a signal handler,
+	 * anyway.
+	 *
+	 * Note we do _exit(2) not _exit(0).  This is to force the postmaster into
+	 * a system reset cycle if someone sends a manual SIGQUIT to a random
+	 * backend.  This is necessary precisely because we don't clean up our
+	 * shared memory state.  (The "dead man switch" mechanism in pmsignal.c
+	 * should ensure the postmaster sees this as a crash, too, but no harm in
+	 * being doubly sure.)
+	 */
+	_exit(2);
+}
+
+/*
+ * Simple signal handler for triggering a long-running background process to
+ * shut down and exit.
+ *
+ * Typically, this handler would be used for SIGTERM, but some procesess use
+ * other signals. In particular, the checkpointer exits on SIGUSR2, the
+ * stats collector on SIGQUIT, and the WAL writer exits on either SIGINT
+ * or SIGTERM.
+ *
+ * ShutdownRequestPending should be checked at a convenient place within the
+ * main loop, or else the main loop should call HandleMainLoopInterrupts.
+ */
+void
+SignalHandlerForShutdownRequest(SIGNAL_ARGS)
+{
+	int			save_errno = errno;
+
+	ShutdownRequestPending = true;
+	SetLatch(MyLatch);
+
+	errno = save_errno;
+}