Fix double KeyboardInterrupt on PL/Python cancel

src/backend/postmaster/postmaster.c

@@ -2977,7 +2977,18 @@ processCancelRequest(Port *port, void *pkt, MsgType code)
 					ereport(DEBUG2,
 							(errmsg_internal("processing cancel request: sending SIGINT to process %d",
 											 backendPID)));
-					signal_child(bp->pid, SIGINT);
+#ifdef HAVE_SETSID
+					/*
+					 * The backend has called setsid() before sending its
+					 * cancel key to the client.  Signal the group once to
+					 * avoid duplicate KeyboardInterrupts in PL/Python.
+					 */
+					if (kill(-bp->pid, SIGINT) == 0)
+						return;
+#endif
+					if (kill(bp->pid, SIGINT) < 0)
+						elog(DEBUG3, "kill(%ld,%d) failed: %m",
+							 (long) bp->pid, SIGINT);
 				}
 			}
 			else

src/backend/utils/init/postinit.c

@@ -1858,8 +1858,9 @@ StatementTimeoutHandler(void)
 		sig = SIGTERM;
 
 #ifdef HAVE_SETSID
-	/* try to signal whole process group */
-	kill(-MyProcPid, sig);
+	/* Avoid delivering the same timeout twice to procedural languages. */
+	if (kill(-MyProcPid, sig) == 0)
+		return;
 #endif
 	kill(MyProcPid, sig);
 }
@@ -1871,8 +1872,8 @@ static void
 LockTimeoutHandler(void)
 {
 #ifdef HAVE_SETSID
-	/* try to signal whole process group */
-	kill(-MyProcPid, SIGINT);
+	if (kill(-MyProcPid, SIGINT) == 0)
+		return;
 #endif
 	kill(MyProcPid, SIGINT);
 }

src/pl/plpython/plpy_main.c

@@ -147,6 +147,10 @@ PLy_initialize(void)
 int
 PLy_python_cancel_handler(void *arg)
 {
+	/* A queued callback can outlive the cancellation that scheduled it. */
+	if (!QueryCancelPending)
+		return 0;
+
 	PyErr_SetNone(PyExc_KeyboardInterrupt);
 
 	/* return -1 to indicate that we set an exception. */

src/test/isolation2/expected/cancel_plpython.out

@@ -100,3 +100,39 @@ PL/Python function "pynestsleep2"
 7q: ... <quitting>
 -- end_ignore
 
+-- A timeout must deliver only one KeyboardInterrupt, let its handler finish,
+-- and leave the next PL/Python call free of pending callbacks.
+CREATE OR REPLACE FUNCTION pysleephandler() RETURNS text AS $$ import time try: while True: time.sleep(0.1) except KeyboardInterrupt: GD['stage'] = 'handled' raise $$ LANGUAGE plpython3u;
+CREATE
+
+CREATE OR REPLACE FUNCTION pystage() RETURNS text AS $$ return GD.get('stage') $$ LANGUAGE plpython3u;
+CREATE
+
+SET statement_timeout = '1s';
+SET
+SELECT pysleephandler();
+ERROR:  canceling statement due to statement timeout
+CONTEXT:  PL/Python function "pysleephandler"
+SELECT pybusyloop();
+ERROR:  canceling statement due to statement timeout
+CONTEXT:  PL/Python function "pybusyloop"
+RESET statement_timeout;
+RESET
+SELECT pystage();
+ pystage 
+---------
+ handled 
+(1 row)
+
+-- Catching one cancellation must not suppress a later, independent request.
+CREATE OR REPLACE FUNCTION pycancelhandler() RETURNS text AS $$ import os import signal GD['stage'] = 'started' try: os.kill(os.getpid(), signal.SIGINT) while True: pass except KeyboardInterrupt: GD['stage'] = 'handled' try: os.kill(os.getpid(), signal.SIGINT) except KeyboardInterrupt: GD['stage'] = 'cancelled twice' raise GD['stage'] = 'second cancel ignored' $$ LANGUAGE plpython3u;
+CREATE
+
+SELECT pycancelhandler();
+ERROR:  canceling statement due to user request
+CONTEXT:  PL/Python function "pycancelhandler"
+SELECT pystage();
+ pystage         
+-----------------
+ cancelled twice 
+(1 row)

src/test/isolation2/sql/cancel_plpython.sql

@@ -75,3 +75,46 @@ FROM pg_stat_activity WHERE query LIKE 'select pynestsleep2()%' ORDER BY pid LIM
 7q:
 -- end_ignore
 
+-- A timeout must deliver only one KeyboardInterrupt, let its handler finish,
+-- and leave the next PL/Python call free of pending callbacks.
+CREATE OR REPLACE FUNCTION pysleephandler() RETURNS text AS $$
+import time
+try:
+    while True:
+        time.sleep(0.1)
+except KeyboardInterrupt:
+    GD['stage'] = 'handled'
+    raise
+$$ LANGUAGE plpython3u;
+
+CREATE OR REPLACE FUNCTION pystage() RETURNS text AS $$
+return GD.get('stage')
+$$ LANGUAGE plpython3u;
+
+SET statement_timeout = '1s';
+SELECT pysleephandler();
+SELECT pybusyloop();
+RESET statement_timeout;
+SELECT pystage();
+
+-- Catching one cancellation must not suppress a later, independent request.
+CREATE OR REPLACE FUNCTION pycancelhandler() RETURNS text AS $$
+import os
+import signal
+GD['stage'] = 'started'
+try:
+    os.kill(os.getpid(), signal.SIGINT)
+    while True:
+        pass
+except KeyboardInterrupt:
+    GD['stage'] = 'handled'
+try:
+    os.kill(os.getpid(), signal.SIGINT)
+except KeyboardInterrupt:
+    GD['stage'] = 'cancelled twice'
+    raise
+GD['stage'] = 'second cancel ignored'
+$$ LANGUAGE plpython3u;
+
+SELECT pycancelhandler();
+SELECT pystage();