Redesign handling of SIGTERM/control-C in parallel pg_dump/pg_restore.

Formerly, Unix builds of pg_dump/pg_restore would trap SIGINT and similar
signals and set a flag that was tested in various data-transfer loops.
This was prone to errors of omission (cf commit 3c8aa665); and even if
the client-side response was prompt, we did nothing that would cause
long-running SQL commands (e.g. CREATE INDEX) to terminate early.
Also, the master process would effectively do nothing at all upon receipt
of SIGINT; the only reason it seemed to work was that in typical scenarios
the signal would also be delivered to the child processes.  We should
support termination when a signal is delivered only to the master process,
though.

Windows builds had no console interrupt handler, so they would just fall
over immediately at control-C, again leaving long-running SQL commands to
finish unmolested.

To fix, remove the flag-checking approach altogether.  Instead, allow the
Unix signal handler to send a cancel request directly and then exit(1).
In the master process, also have it forward the signal to the children.
On Windows, add a console interrupt handler that behaves approximately
the same.  The main difference is that a single execution of the Windows
handler can send all the cancel requests since all the info is available
in one process, whereas on Unix each process sends a cancel only for its
own database connection.

In passing, fix an old problem that DisconnectDatabase tends to send a
cancel request before exiting a parallel worker, even if nothing went
wrong.  This is at least a waste of cycles, and could lead to unexpected
log messages, or maybe even data loss if it happened in pg_restore (though
in the current code the problem seems to affect only pg_dump).  The cause
was that after a COPY step, pg_dump was leaving libpq in PGASYNC_BUSY
state, causing PQtransactionStatus() to report PQTRANS_ACTIVE.  That's
normally harmless because the next PQexec() will silently clear the
PGASYNC_BUSY state; but in a parallel worker we might exit without any
additional SQL commands after a COPY step.  So add an extra PQgetResult()
call after a COPY to allow libpq to return to PGASYNC_IDLE state.

This is a bug fix, IMO, so back-patch to 9.3 where parallel dump/restore
were introduced.

Thanks to Kyotaro Horiguchi for Windows testing and code suggestions.

Original-Patch: <7005.1464657274@sss.pgh.pa.us>
Discussion: <20160602.174941.256342236.horiguchi.kyotaro@lab.ntt.co.jp>

src/bin/pg_dump/compress_io.c

@@ -54,7 +54,6 @@
 #include "postgres_fe.h"
 
 #include "compress_io.h"
-#include "parallel.h"
 #include "pg_backup_utils.h"
 
 /*----------------------
@@ -184,9 +183,6 @@ void
 WriteDataToArchive(ArchiveHandle *AH, CompressorState *cs,
 				   const void *data, size_t dLen)
 {
-	/* Are we aborting? */
-	checkAborting(AH);
-
 	switch (cs->comprAlg)
 	{
 		case COMPR_ALG_LIBZ:
@@ -351,9 +347,6 @@ ReadDataFromArchiveZlib(ArchiveHandle *AH, ReadFunc readF)
 	/* no minimal chunk size for zlib */
 	while ((cnt = readF(AH, &buf, &buflen)))
 	{
-		/* Are we aborting? */
-		checkAborting(AH);
-
 		zp->next_in = (void *) buf;
 		zp->avail_in = cnt;
 
@@ -414,9 +407,6 @@ ReadDataFromArchiveNone(ArchiveHandle *AH, ReadFunc readF)
 
 	while ((cnt = readF(AH, &buf, &buflen)))
 	{
-		/* Are we aborting? */
-		checkAborting(AH);
-
 		ahwrite(buf, 1, cnt, AH);
 	}
 

src/bin/pg_dump/parallel.c

@@ -43,7 +43,7 @@
  * the catalog.  That's why our worker processes can also access the catalog
  * information.  (In the Windows case, the workers are threads in the same
  * process.  To avoid problems, they work with cloned copies of the Archive
- * data structure; see init_spawned_worker_win32().)
+ * data structure; see RunWorker().)
  *
  * In the master process, the workerStatus field for each worker has one of
  * the following values:
@@ -83,9 +83,8 @@
  */
 typedef struct
 {
-	ArchiveHandle *AH;
-	int			pipeRead;
-	int			pipeWrite;
+	ArchiveHandle *AH;			/* master database connection */
+	ParallelSlot *slot;			/* this worker's parallel slot */
 } WorkerInfo;
 
 /* Windows implementation of pipe access */
@@ -95,9 +94,6 @@ static int	piperead(int s, char *buf, int len);
 
 #else							/* !WIN32 */
 
-/* Signal handler flag */
-static volatile sig_atomic_t wantAbort = 0;
-
 /* Non-Windows implementation of pipe access */
 #define pgpipe(a)			pipe(a)
 #define piperead(a,b,c)		read(a,b,c)
@@ -116,10 +112,37 @@ typedef struct ShutdownInformation
 
 static ShutdownInformation shutdown_info;
 
+/*
+ * State info for signal handling.
+ * We assume signal_info initializes to zeroes.
+ *
+ * On Unix, myAH is the master DB connection in the master process, and the
+ * worker's own connection in worker processes.  On Windows, we have only one
+ * instance of signal_info, so myAH is the master connection and the worker
+ * connections must be dug out of pstate->parallelSlot[].
+ */
+typedef struct DumpSignalInformation
+{
+	ArchiveHandle *myAH;		/* database connection to issue cancel for */
+	ParallelState *pstate;		/* parallel state, if any */
+	bool		handler_set;	/* signal handler set up in this process? */
+#ifndef WIN32
+	bool		am_worker;		/* am I a worker process? */
+#endif
+} DumpSignalInformation;
+
+static volatile DumpSignalInformation signal_info;
+
+#ifdef WIN32
+static CRITICAL_SECTION signal_info_lock;
+#endif
+
+/* Used from signal handlers, no buffering */
+#define write_stderr(str)	write(fileno(stderr), str, strlen(str))
+
+
 #ifdef WIN32
 /* file-scope variables */
-static unsigned int tMasterThreadId = 0;
-static HANDLE termEvent = INVALID_HANDLE_VALUE;
 static DWORD tls_index;
 
 /* globally visible variables (needed by exit_nicely) */
@@ -134,7 +157,10 @@ static ParallelSlot *GetMyPSlot(ParallelState *pstate);
 static void archive_close_connection(int code, void *arg);
 static void ShutdownWorkersHard(ParallelState *pstate);
 static void WaitForTerminatingWorkers(ParallelState *pstate);
-static void RunWorker(ArchiveHandle *AH, int pipefd[2]);
+static void setup_cancel_handler(void);
+static void set_cancel_pstate(ParallelState *pstate);
+static void set_cancel_slot_archive(ParallelSlot *slot, ArchiveHandle *AH);
+static void RunWorker(ArchiveHandle *AH, ParallelSlot *slot);
 static bool HasEveryWorkerTerminated(ParallelState *pstate);
 static void lockTableForWorker(ArchiveHandle *AH, TocEntry *te);
 static void WaitForCommands(ArchiveHandle *AH, int pipefd[2]);
@@ -291,13 +317,13 @@ archive_close_connection(int code, void *arg)
 		if (!slot)
 		{
 			/*
-			 * We're the master.  Close our own database connection, if any,
-			 * and then forcibly shut down workers.
+			 * We're the master.  Forcibly shut down workers, then close our
+			 * own database connection, if any.
 			 */
+			ShutdownWorkersHard(si->pstate);
+
 			if (si->AHX)
 				DisconnectDatabase(si->AHX);
-
-			ShutdownWorkersHard(si->pstate);
 		}
 		else
 		{
@@ -326,34 +352,13 @@ archive_close_connection(int code, void *arg)
 	}
 }
 
-/*
- * Check to see if we've been told to abort, and exit the process/thread if
- * so.  We don't print any error message; that would just clutter the screen.
- *
- * If we have one worker that terminates for some reason, we'd like the other
- * threads to terminate as well (and not finish with their 70 GB table dump
- * first...).  In Unix, the master sends SIGTERM and the worker's signal
- * handler sets wantAbort to 1.  In Windows we set a termEvent and this serves
- * as the signal for worker threads to exit.  Note that while we check this
- * fairly frequently during data transfers, an idle worker doesn't come here
- * at all, so additional measures are needed to force shutdown.
- *
- * XXX in parallel restore, slow server-side operations like CREATE INDEX
- * are not interrupted by anything we do here.  This needs more work.
- */
-void
-checkAborting(ArchiveHandle *AH)
-{
-#ifdef WIN32
-	if (WaitForSingleObject(termEvent, 0) == WAIT_OBJECT_0)
-#else
-	if (wantAbort)
-#endif
-		exit_nicely(1);
-}
-
 /*
  * Forcibly shut down any remaining workers, waiting for them to finish.
+ *
+ * Note that we don't expect to come here during normal exit (the workers
+ * should be long gone, and the ParallelState too).  We're only here in an
+ * exit_horribly() situation, so intervening to cancel active commands is
+ * appropriate.
  */
 static void
 ShutdownWorkersHard(ParallelState *pstate)
@@ -367,15 +372,37 @@ ShutdownWorkersHard(ParallelState *pstate)
 	for (i = 0; i < pstate->numWorkers; i++)
 		closesocket(pstate->parallelSlot[i].pipeWrite);
 
+	/*
+	 * Force early termination of any commands currently in progress.
+	 */
 #ifndef WIN32
-	/* On non-Windows, send SIGTERM to abort commands-in-progress. */
+	/* On non-Windows, send SIGTERM to each worker process. */
 	for (i = 0; i < pstate->numWorkers; i++)
-		kill(pstate->parallelSlot[i].pid, SIGTERM);
+	{
+		pid_t		pid = pstate->parallelSlot[i].pid;
+
+		if (pid != 0)
+			kill(pid, SIGTERM);
+	}
 #else
-	/* Non-idle workers monitor this event via checkAborting(). */
-	SetEvent(termEvent);
+
+	/*
+	 * On Windows, send query cancels directly to the workers' backends.  Use
+	 * a critical section to ensure worker threads don't change state.
+	 */
+	EnterCriticalSection(&signal_info_lock);
+	for (i = 0; i < pstate->numWorkers; i++)
+	{
+		ArchiveHandle *AH = pstate->parallelSlot[i].args->AH;
+		char		errbuf[1];
+
+		if (AH != NULL && AH->connCancel != NULL)
+			(void) PQcancel(AH->connCancel, errbuf, sizeof(errbuf));
+	}
+	LeaveCriticalSection(&signal_info_lock);
 #endif
 
+	/* Now wait for them to terminate. */
 	WaitForTerminatingWorkers(pstate);
 }
 
@@ -445,16 +472,316 @@ WaitForTerminatingWorkers(ParallelState *pstate)
 	}
 }
 
+
 /*
- * Signal handler (Unix only)
+ * Code for responding to cancel interrupts (SIGINT, control-C, etc)
+ *
+ * This doesn't quite belong in this module, but it needs access to the
+ * ParallelState data, so there's not really a better place either.
+ *
+ * When we get a cancel interrupt, we could just die, but in pg_restore that
+ * could leave a SQL command (e.g., CREATE INDEX on a large table) running
+ * for a long time.  Instead, we try to send a cancel request and then die.
+ * pg_dump probably doesn't really need this, but we might as well use it
+ * there too.  Note that sending the cancel directly from the signal handler
+ * is safe because PQcancel() is written to make it so.
+ *
+ * In parallel operation on Unix, each process is responsible for canceling
+ * its own connection (this must be so because nobody else has access to it).
+ * Furthermore, the master process should attempt to forward its signal to
+ * each child.  In simple manual use of pg_dump/pg_restore, forwarding isn't
+ * needed because typing control-C at the console would deliver SIGINT to
+ * every member of the terminal process group --- but in other scenarios it
+ * might be that only the master gets signaled.
+ *
+ * On Windows, the cancel handler runs in a separate thread, because that's
+ * how SetConsoleCtrlHandler works.  We make it stop worker threads, send
+ * cancels on all active connections, and then return FALSE, which will allow
+ * the process to die.  For safety's sake, we use a critical section to
+ * protect the PGcancel structures against being changed while the signal
+ * thread runs.
  */
+
 #ifndef WIN32
+
+/*
+ * Signal handler (Unix only)
+ */
 static void
 sigTermHandler(SIGNAL_ARGS)
 {
-	wantAbort = 1;
+	int			i;
+	char		errbuf[1];
+
+	/*
+	 * Some platforms allow delivery of new signals to interrupt an active
+	 * signal handler.  That could muck up our attempt to send PQcancel, so
+	 * disable the signals that setup_cancel_handler enabled.
+	 */
+	pqsignal(SIGINT, SIG_IGN);
+	pqsignal(SIGTERM, SIG_IGN);
+	pqsignal(SIGQUIT, SIG_IGN);
+
+	/*
+	 * If we're in the master, forward signal to all workers.  (It seems best
+	 * to do this before PQcancel; killing the master transaction will result
+	 * in invalid-snapshot errors from active workers, which maybe we can
+	 * quiet by killing workers first.)  Ignore any errors.
+	 */
+	if (signal_info.pstate != NULL)
+	{
+		for (i = 0; i < signal_info.pstate->numWorkers; i++)
+		{
+			pid_t		pid = signal_info.pstate->parallelSlot[i].pid;
+
+			if (pid != 0)
+				kill(pid, SIGTERM);
+		}
+	}
+
+	/*
+	 * Send QueryCancel if we have a connection to send to.  Ignore errors,
+	 * there's not much we can do about them anyway.
+	 */
+	if (signal_info.myAH != NULL && signal_info.myAH->connCancel != NULL)
+		(void) PQcancel(signal_info.myAH->connCancel, errbuf, sizeof(errbuf));
+
+	/*
+	 * Report we're quitting, using nothing more complicated than write(2).
+	 * When in parallel operation, only the master process should do this.
+	 */
+	if (!signal_info.am_worker)
+	{
+		if (progname)
+		{
+			write_stderr(progname);
+			write_stderr(": ");
+		}
+		write_stderr("terminated by user\n");
+	}
+
+	/* And die. */
+	exit(1);
+}
+
+/*
+ * Enable cancel interrupt handler, if not already done.
+ */
+static void
+setup_cancel_handler(void)
+{
+	/*
+	 * When forking, signal_info.handler_set will propagate into the new
+	 * process, but that's fine because the signal handler state does too.
+	 */
+	if (!signal_info.handler_set)
+	{
+		signal_info.handler_set = true;
+
+		pqsignal(SIGINT, sigTermHandler);
+		pqsignal(SIGTERM, sigTermHandler);
+		pqsignal(SIGQUIT, sigTermHandler);
+	}
+}
+
+#else							/* WIN32 */
+
+/*
+ * Console interrupt handler --- runs in a newly-started thread.
+ *
+ * After stopping other threads and sending cancel requests on all open
+ * connections, we return FALSE which will allow the default ExitProcess()
+ * action to be taken.
+ */
+static BOOL WINAPI
+consoleHandler(DWORD dwCtrlType)
+{
+	int			i;
+	char		errbuf[1];
+
+	if (dwCtrlType == CTRL_C_EVENT ||
+		dwCtrlType == CTRL_BREAK_EVENT)
+	{
+		/* Critical section prevents changing data we look at here */
+		EnterCriticalSection(&signal_info_lock);
+
+		/*
+		 * If in parallel mode, stop worker threads and send QueryCancel to
+		 * their connected backends.  The main point of stopping the worker
+		 * threads is to keep them from reporting the query cancels as errors,
+		 * which would clutter the user's screen.  We needn't stop the master
+		 * thread since it won't be doing much anyway.  Do this before
+		 * canceling the main transaction, else we might get invalid-snapshot
+		 * errors reported before we can stop the workers.  Ignore errors,
+		 * there's not much we can do about them anyway.
+		 */
+		if (signal_info.pstate != NULL)
+		{
+			for (i = 0; i < signal_info.pstate->numWorkers; i++)
+			{
+				ParallelSlot *slot = &(signal_info.pstate->parallelSlot[i]);
+				ArchiveHandle *AH = slot->args->AH;
+				HANDLE		hThread = (HANDLE) slot->hThread;
+
+				/*
+				 * Using TerminateThread here may leave some resources leaked,
+				 * but it doesn't matter since we're about to end the whole
+				 * process.
+				 */
+				if (hThread != INVALID_HANDLE_VALUE)
+					TerminateThread(hThread, 0);
+
+				if (AH != NULL && AH->connCancel != NULL)
+					(void) PQcancel(AH->connCancel, errbuf, sizeof(errbuf));
+			}
+		}
+
+		/*
+		 * Send QueryCancel to master connection, if enabled.  Ignore errors,
+		 * there's not much we can do about them anyway.
+		 */
+		if (signal_info.myAH != NULL && signal_info.myAH->connCancel != NULL)
+			(void) PQcancel(signal_info.myAH->connCancel,
+							errbuf, sizeof(errbuf));
+
+		LeaveCriticalSection(&signal_info_lock);
+
+		/*
+		 * Report we're quitting, using nothing more complicated than
+		 * write(2).  (We might be able to get away with using write_msg()
+		 * here, but since we terminated other threads uncleanly above, it
+		 * seems better to assume as little as possible.)
+		 */
+		if (progname)
+		{
+			write_stderr(progname);
+			write_stderr(": ");
+		}
+		write_stderr("terminated by user\n");
+	}
+
+	/* Always return FALSE to allow signal handling to continue */
+	return FALSE;
+}
+
+/*
+ * Enable cancel interrupt handler, if not already done.
+ */
+static void
+setup_cancel_handler(void)
+{
+	if (!signal_info.handler_set)
+	{
+		signal_info.handler_set = true;
+
+		InitializeCriticalSection(&signal_info_lock);
+
+		SetConsoleCtrlHandler(consoleHandler, TRUE);
+	}
+}
+
+#endif   /* WIN32 */
+
+
+/*
+ * set_archive_cancel_info
+ *
+ * Fill AH->connCancel with cancellation info for the specified database
+ * connection; or clear it if conn is NULL.
+ */
+void
+set_archive_cancel_info(ArchiveHandle *AH, PGconn *conn)
+{
+	PGcancel   *oldConnCancel;
+
+	/*
+	 * Activate the interrupt handler if we didn't yet in this process.  On
+	 * Windows, this also initializes signal_info_lock; therefore it's
+	 * important that this happen at least once before we fork off any
+	 * threads.
+	 */
+	setup_cancel_handler();
+
+	/*
+	 * On Unix, we assume that storing a pointer value is atomic with respect
+	 * to any possible signal interrupt.  On Windows, use a critical section.
+	 */
+
+#ifdef WIN32
+	EnterCriticalSection(&signal_info_lock);
+#endif
+
+	/* Free the old one if we have one */
+	oldConnCancel = AH->connCancel;
+	/* be sure interrupt handler doesn't use pointer while freeing */
+	AH->connCancel = NULL;
+
+	if (oldConnCancel != NULL)
+		PQfreeCancel(oldConnCancel);
+
+	/* Set the new one if specified */
+	if (conn)
+		AH->connCancel = PQgetCancel(conn);
+
+	/*
+	 * On Unix, there's only ever one active ArchiveHandle per process, so we
+	 * can just set signal_info.myAH unconditionally.  On Windows, do that
+	 * only in the main thread; worker threads have to make sure their
+	 * ArchiveHandle appears in the pstate data, which is dealt with in
+	 * RunWorker().
+	 */
+#ifndef WIN32
+	signal_info.myAH = AH;
+#else
+	if (mainThreadId == GetCurrentThreadId())
+		signal_info.myAH = AH;
+#endif
+
+#ifdef WIN32
+	LeaveCriticalSection(&signal_info_lock);
+#endif
 }
+
+/*
+ * set_cancel_pstate
+ *
+ * Set signal_info.pstate to point to the specified ParallelState, if any.
+ * We need this mainly to have an interlock against Windows signal thread.
+ */
+static void
+set_cancel_pstate(ParallelState *pstate)
+{
+#ifdef WIN32
+	EnterCriticalSection(&signal_info_lock);
+#endif
+
+	signal_info.pstate = pstate;
+
+#ifdef WIN32
+	LeaveCriticalSection(&signal_info_lock);
 #endif
+}
+
+/*
+ * set_cancel_slot_archive
+ *
+ * Set ParallelSlot's AH field to point to the specified archive, if any.
+ * We need this mainly to have an interlock against Windows signal thread.
+ */
+static void
+set_cancel_slot_archive(ParallelSlot *slot, ArchiveHandle *AH)
+{
+#ifdef WIN32
+	EnterCriticalSection(&signal_info_lock);
+#endif
+
+	slot->args->AH = AH;
+
+#ifdef WIN32
+	LeaveCriticalSection(&signal_info_lock);
+#endif
+}
+
 
 /*
  * This function is called by both Unix and Windows variants to set up
@@ -462,19 +789,44 @@ sigTermHandler(SIGNAL_ARGS)
  * upon return.
  */
 static void
-RunWorker(ArchiveHandle *AH, int pipefd[2])
+RunWorker(ArchiveHandle *AH, ParallelSlot *slot)
 {
+	int			pipefd[2];
+
+	/* fetch child ends of pipes */
+	pipefd[PIPE_READ] = slot->pipeRevRead;
+	pipefd[PIPE_WRITE] = slot->pipeRevWrite;
+
+	/*
+	 * Clone the archive so that we have our own state to work with, and in
+	 * particular our own database connection.
+	 *
+	 * We clone on Unix as well as Windows, even though technically we don't
+	 * need to because fork() gives us a copy in our own address space
+	 * already.  But CloneArchive resets the state information and also clones
+	 * the database connection which both seem kinda helpful.
+	 */
+	AH = CloneArchive(AH);
+
+	/* Remember cloned archive where signal handler can find it */
+	set_cancel_slot_archive(slot, AH);
+
 	/*
 	 * Call the setup worker function that's defined in the ArchiveHandle.
 	 */
 	(AH->SetupWorkerPtr) ((Archive *) AH);
 
-	Assert(AH->connection != NULL);
-
 	/*
 	 * Execute commands until done.
 	 */
 	WaitForCommands(AH, pipefd);
+
+	/*
+	 * Disconnect from database and clean up.
+	 */
+	set_cancel_slot_archive(slot, NULL);
+	DisconnectDatabase(&(AH->public));
+	DeCloneArchive(AH);
 }
 
 /*
@@ -484,22 +836,16 @@ RunWorker(ArchiveHandle *AH, int pipefd[2])
 static unsigned __stdcall
 init_spawned_worker_win32(WorkerInfo *wi)
 {
-	ArchiveHandle *AH;
-	int			pipefd[2] = {wi->pipeRead, wi->pipeWrite};
-
-	/*
-	 * Clone the archive so that we have our own state to work with, and in
-	 * particular our own database connection.
-	 */
-	AH = CloneArchive(wi->AH);
+	ArchiveHandle *AH = wi->AH;
+	ParallelSlot *slot = wi->slot;
 
+	/* Don't need WorkerInfo anymore */
 	free(wi);
 
 	/* Run the worker ... */
-	RunWorker(AH, pipefd);
+	RunWorker(AH, slot);
 
-	/* Clean up and exit the thread */
-	DeCloneArchive(AH);
+	/* Exit the thread */
 	_endthreadex(0);
 	return 0;
 }
@@ -519,9 +865,6 @@ ParallelBackupStart(ArchiveHandle *AH)
 
 	Assert(AH->public.numWorkers > 0);
 
-	/* Ensure stdio state is quiesced before forking */
-	fflush(NULL);
-
 	pstate = (ParallelState *) pg_malloc(sizeof(ParallelState));
 
 	pstate->numWorkers = AH->public.numWorkers;
@@ -533,25 +876,31 @@ ParallelBackupStart(ArchiveHandle *AH)
 	pstate->parallelSlot = (ParallelSlot *) pg_malloc(slotSize);
 	memset((void *) pstate->parallelSlot, 0, slotSize);
 
-	/*
-	 * Set the pstate in the shutdown_info. The exit handler uses pstate if
-	 * set and falls back to AHX otherwise.
-	 */
-	shutdown_info.pstate = pstate;
-
 #ifdef WIN32
-	/* Set up thread management state */
-	tMasterThreadId = GetCurrentThreadId();
-	termEvent = CreateEvent(NULL, true, false, "Terminate");
 	/* Make fmtId() and fmtQualifiedId() use thread-local storage */
 	getLocalPQExpBuffer = getThreadLocalPQExpBuffer;
-#else
-	/* Set up signal handling state */
-	signal(SIGTERM, sigTermHandler);
-	signal(SIGINT, sigTermHandler);
-	signal(SIGQUIT, sigTermHandler);
 #endif
 
+	/*
+	 * Set the pstate in shutdown_info, to tell the exit handler that it must
+	 * clean up workers as well as the main database connection.  But we don't
+	 * set this in signal_info yet, because we don't want child processes to
+	 * inherit non-NULL signal_info.pstate.
+	 */
+	shutdown_info.pstate = pstate;
+
+	/*
+	 * Temporarily disable query cancellation on the master connection.  This
+	 * ensures that child processes won't inherit valid AH->connCancel
+	 * settings and thus won't try to issue cancels against the master's
+	 * connection.  No harm is done if we fail while it's disabled, because
+	 * the master connection is idle at this point anyway.
+	 */
+	set_archive_cancel_info(AH, NULL);
+
+	/* Ensure stdio state is quiesced before forking */
+	fflush(NULL);
+
 	/* Create desired number of workers */
 	for (i = 0; i < pstate->numWorkers; i++)
 	{
@@ -561,6 +910,7 @@ ParallelBackupStart(ArchiveHandle *AH)
 #else
 		pid_t		pid;
 #endif
+		ParallelSlot *slot = &(pstate->parallelSlot[i]);
 		int			pipeMW[2],
 					pipeWM[2];
 
@@ -570,41 +920,40 @@ ParallelBackupStart(ArchiveHandle *AH)
 						  "could not create communication channels: %s\n",
 						  strerror(errno));
 
-		pstate->parallelSlot[i].workerStatus = WRKR_IDLE;
-		pstate->parallelSlot[i].args = (ParallelArgs *) pg_malloc(sizeof(ParallelArgs));
-		pstate->parallelSlot[i].args->AH = NULL;
-		pstate->parallelSlot[i].args->te = NULL;
+		slot->workerStatus = WRKR_IDLE;
+		slot->args = (ParallelArgs *) pg_malloc(sizeof(ParallelArgs));
+		slot->args->AH = NULL;
+		slot->args->te = NULL;
 
 		/* master's ends of the pipes */
-		pstate->parallelSlot[i].pipeRead = pipeWM[PIPE_READ];
-		pstate->parallelSlot[i].pipeWrite = pipeMW[PIPE_WRITE];
+		slot->pipeRead = pipeWM[PIPE_READ];
+		slot->pipeWrite = pipeMW[PIPE_WRITE];
 		/* child's ends of the pipes */
-		pstate->parallelSlot[i].pipeRevRead = pipeMW[PIPE_READ];
-		pstate->parallelSlot[i].pipeRevWrite = pipeWM[PIPE_WRITE];
+		slot->pipeRevRead = pipeMW[PIPE_READ];
+		slot->pipeRevWrite = pipeWM[PIPE_WRITE];
 
 #ifdef WIN32
 		/* Create transient structure to pass args to worker function */
 		wi = (WorkerInfo *) pg_malloc(sizeof(WorkerInfo));
 
 		wi->AH = AH;
-		wi->pipeRead = pipeMW[PIPE_READ];
-		wi->pipeWrite = pipeWM[PIPE_WRITE];
+		wi->slot = slot;
 
 		handle = _beginthreadex(NULL, 0, (void *) &init_spawned_worker_win32,
-								wi, 0, &(pstate->parallelSlot[i].threadId));
-		pstate->parallelSlot[i].hThread = handle;
+								wi, 0, &(slot->threadId));
+		slot->hThread = handle;
 #else							/* !WIN32 */
 		pid = fork();
 		if (pid == 0)
 		{
 			/* we are the worker */
 			int			j;
-			int			pipefd[2];
 
-			pipefd[0] = pipeMW[PIPE_READ];
-			pipefd[1] = pipeWM[PIPE_WRITE];
+			/* this is needed for GetMyPSlot() */
+			slot->pid = getpid();
 
-			pstate->parallelSlot[i].pid = getpid();
+			/* instruct signal handler that we're in a worker now */
+			signal_info.am_worker = true;
 
 			/* close read end of Worker -> Master */
 			closesocket(pipeWM[PIPE_READ]);
@@ -621,17 +970,8 @@ ParallelBackupStart(ArchiveHandle *AH)
 				closesocket(pstate->parallelSlot[j].pipeWrite);
 			}
 
-			/*
-			 * Call CloneArchive on Unix as well as Windows, even though
-			 * technically we don't need to because fork() gives us a copy in
-			 * our own address space already.  But CloneArchive resets the
-			 * state information and also clones the database connection which
-			 * both seem kinda helpful.
-			 */
-			pstate->parallelSlot[i].args->AH = CloneArchive(AH);
-
 			/* Run the worker ... */
-			RunWorker(pstate->parallelSlot[i].args->AH, pipefd);
+			RunWorker(AH, slot);
 
 			/* We can just exit(0) when done */
 			exit(0);
@@ -645,7 +985,7 @@ ParallelBackupStart(ArchiveHandle *AH)
 		}
 
 		/* In Master after successful fork */
-		pstate->parallelSlot[i].pid = pid;
+		slot->pid = pid;
 
 		/* close read end of Master -> Worker */
 		closesocket(pipeMW[PIPE_READ]);
@@ -660,9 +1000,22 @@ ParallelBackupStart(ArchiveHandle *AH)
 	 * the workers to inherit this setting, though.
 	 */
 #ifndef WIN32
-	signal(SIGPIPE, SIG_IGN);
+	pqsignal(SIGPIPE, SIG_IGN);
 #endif
 
+	/*
+	 * Re-establish query cancellation on the master connection.
+	 */
+	set_archive_cancel_info(AH, AH->connection);
+
+	/*
+	 * Tell the cancel signal handler to forward signals to worker processes,
+	 * too.  (As with query cancel, we did not need this earlier because the
+	 * workers have not yet been given anything to do; if we die before this
+	 * point, any already-started workers will see EOF and quit promptly.)
+	 */
+	set_cancel_pstate(pstate);
+
 	return pstate;
 }
 
@@ -692,10 +1045,11 @@ ParallelBackupEnd(ArchiveHandle *AH, ParallelState *pstate)
 	WaitForTerminatingWorkers(pstate);
 
 	/*
-	 * Unlink pstate from shutdown_info, so the exit handler will again fall
-	 * back to closing AH->connection (if connected).
+	 * Unlink pstate from shutdown_info, so the exit handler will not try to
+	 * use it; and likewise unlink from signal_info.
 	 */
 	shutdown_info.pstate = NULL;
+	set_cancel_pstate(NULL);
 
 	/* Release state (mere neatnik-ism, since we're about to terminate) */
 	free(pstate->parallelSlot);
@@ -848,9 +1202,7 @@ WaitForCommands(ArchiveHandle *AH, int pipefd[2])
 	{
 		if (!(command = getMessageFromMaster(pipefd)))
 		{
-			/* EOF ... clean up */
-			PQfinish(AH->connection);
-			AH->connection = NULL;
+			/* EOF, so done */
 			return;
 		}
 
@@ -1114,44 +1466,20 @@ select_loop(int maxFd, fd_set *workerset)
 	int			i;
 	fd_set		saveSet = *workerset;
 
-#ifdef WIN32
-	for (;;)
-	{
-		/*
-		 * Sleep a quarter of a second before checking if we should terminate.
-		 *
-		 * XXX we're not actually checking for a cancel interrupt ... but we
-		 * should be.
-		 */
-		struct timeval tv = {0, 250000};
-
-		*workerset = saveSet;
-		i = select(maxFd + 1, workerset, NULL, NULL, &tv);
-
-		if (i == SOCKET_ERROR && WSAGetLastError() == WSAEINTR)
-			continue;
-		if (i)
-			break;
-	}
-#else							/* !WIN32 */
 	for (;;)
 	{
 		*workerset = saveSet;
 		i = select(maxFd + 1, workerset, NULL, NULL, NULL);
 
-		/*
-		 * If we Ctrl-C the master process, it's likely that we interrupt
-		 * select() here. The signal handler will set wantAbort == true and
-		 * the shutdown journey starts from here.
-		 */
-		if (wantAbort)
-			exit_horribly(modulename, "terminated by user\n");
-
+#ifndef WIN32
 		if (i < 0 && errno == EINTR)
 			continue;
+#else
+		if (i == SOCKET_ERROR && WSAGetLastError() == WSAEINTR)
+			continue;
+#endif
 		break;
 	}
-#endif   /* WIN32 */
 
 	return i;
 }

src/bin/pg_dump/parallel.h

@@ -82,6 +82,6 @@ extern void DispatchJobForTocEntry(ArchiveHandle *AH,
 					   TocEntry *te, T_Action act);
 extern void ParallelBackupEnd(ArchiveHandle *AH, ParallelState *pstate);
 
-extern void checkAborting(ArchiveHandle *AH);
+extern void set_archive_cancel_info(ArchiveHandle *AH, PGconn *conn);
 
 #endif   /* PG_DUMP_PARALLEL_H */

src/bin/pg_dump/pg_backup_archiver.c

@@ -4420,6 +4420,7 @@ CloneArchive(ArchiveHandle *AH)
 
 	/* The clone will have its own connection, so disregard connection state */
 	clone->connection = NULL;
+	clone->connCancel = NULL;
 	clone->currUser = NULL;
 	clone->currSchema = NULL;
 	clone->currTablespace = NULL;
@@ -4493,6 +4494,9 @@ CloneArchive(ArchiveHandle *AH)
 void
 DeCloneArchive(ArchiveHandle *AH)
 {
+	/* Should not have an open database connection */
+	Assert(AH->connection == NULL);
+
 	/* Clear format-specific state */
 	(AH->DeClonePtr) (AH);
 

src/bin/pg_dump/pg_backup_archiver.h

@@ -285,6 +285,9 @@ struct _archiveHandle
 	char	   *savedPassword;	/* password for ropt->username, if known */
 	char	   *use_role;
 	PGconn	   *connection;
+	/* If connCancel isn't NULL, SIGINT handler will send a cancel */
+	PGcancel   *volatile connCancel;
+
 	int			connectToDB;	/* Flag to indicate if direct DB connection is
 								 * required */
 	ArchiverOutput outputKind;	/* Flag for what we're currently writing */

src/bin/pg_dump/pg_backup_db.c

@@ -12,6 +12,7 @@
 #include "postgres_fe.h"
 
 #include "dumputils.h"
+#include "parallel.h"
 #include "pg_backup_archiver.h"
 #include "pg_backup_db.h"
 #include "pg_backup_utils.h"
@@ -106,6 +107,9 @@ ReconnectToServer(ArchiveHandle *AH, const char *dbname, const char *username)
 
 	newConn = _connectDB(AH, newdbname, newusername);
 
+	/* Update ArchiveHandle's connCancel before closing old connection */
+	set_archive_cancel_info(AH, newConn);
+
 	PQfinish(AH->connection);
 	AH->connection = newConn;
 
@@ -327,6 +331,9 @@ ConnectDatabase(Archive *AHX,
 	_check_database_version(AH);
 
 	PQsetNoticeProcessor(AH->connection, notice_processor, NULL);
+
+	/* arrange for SIGINT to issue a query cancel on this connection */
+	set_archive_cancel_info(AH, AH->connection);
 }
 
 /*
@@ -337,19 +344,25 @@ void
 DisconnectDatabase(Archive *AHX)
 {
 	ArchiveHandle *AH = (ArchiveHandle *) AHX;
-	PGcancel   *cancel;
 	char		errbuf[1];
 
 	if (!AH->connection)
 		return;
 
-	if (PQtransactionStatus(AH->connection) == PQTRANS_ACTIVE)
+	if (AH->connCancel)
 	{
-		if ((cancel = PQgetCancel(AH->connection)))
-		{
-			PQcancel(cancel, errbuf, sizeof(errbuf));
-			PQfreeCancel(cancel);
-		}
+		/*
+		 * If we have an active query, send a cancel before closing.  This is
+		 * of no use for a normal exit, but might be helpful during
+		 * exit_horribly().
+		 */
+		if (PQtransactionStatus(AH->connection) == PQTRANS_ACTIVE)
+			PQcancel(AH->connCancel, errbuf, sizeof(errbuf));
+
+		/*
+		 * Prevent signal handler from sending a cancel after this.
+		 */
+		set_archive_cancel_info(AH, NULL);
 	}
 
 	PQfinish(AH->connection);
@@ -631,6 +644,11 @@ EndDBCopyMode(Archive *AHX, const char *tocEntryTag)
 								tocEntryTag, PQerrorMessage(AH->connection));
 		PQclear(res);
 
+		/* Do this to ensure we've pumped libpq back to idle state */
+		if (PQgetResult(AH->connection) != NULL)
+			write_msg(NULL, "WARNING: unexpected extra results during COPY of table \"%s\"\n",
+					  tocEntryTag);
+
 		AH->pgCopyIn = false;
 	}
 }

src/bin/pg_dump/pg_backup_directory.c

@@ -356,9 +356,6 @@ _WriteData(ArchiveHandle *AH, const void *data, size_t dLen)
 {
 	lclContext *ctx = (lclContext *) AH->formatData;
 
-	/* Are we aborting? */
-	checkAborting(AH);
-
 	if (dLen > 0 && cfwrite(data, dLen, ctx->dataFH) != dLen)
 		WRITE_ERROR_EXIT;
 
@@ -407,9 +404,6 @@ _PrintFileData(ArchiveHandle *AH, char *filename)
 
 	while ((cnt = cfread(buf, buflen, cfp)))
 	{
-		/* Are we aborting? */
-		checkAborting(AH);
-
 		ahwrite(buf, 1, cnt, AH);
 	}
 
@@ -529,9 +523,6 @@ _WriteBuf(ArchiveHandle *AH, const void *buf, size_t len)
 {
 	lclContext *ctx = (lclContext *) AH->formatData;
 
-	/* Are we aborting? */
-	checkAborting(AH);
-
 	if (cfwrite(buf, len, ctx->dataFH) != len)
 		WRITE_ERROR_EXIT;
 
@@ -548,9 +539,6 @@ _ReadBuf(ArchiveHandle *AH, void *buf, size_t len)
 {
 	lclContext *ctx = (lclContext *) AH->formatData;
 
-	/* Are we aborting? */
-	checkAborting(AH);
-
 	/*
 	 * If there was an I/O error, we already exited in cfread(), so here we
 	 * exit on short reads.

src/bin/pg_dump/pg_dump.c

@@ -1780,6 +1780,11 @@ dumpTableData_copy(Archive *fout, void *dcontext)
 	}
 	PQclear(res);
 
+	/* Do this to ensure we've pumped libpq back to idle state */
+	if (PQgetResult(conn) != NULL)
+		write_msg(NULL, "WARNING: unexpected extra results during COPY of table \"%s\"\n",
+				  classname);
+
 	destroyPQExpBuffer(q);
 	return 1;
 }