v2-0005-Address-walreceiver-by-procno-not-direct-pointer-.patch

From afff68be45932c0340fda79ff1f7a154130beaf5 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Fri, 23 Aug 2024 23:54:53 +0300
Subject: [PATCH v2 05/12] Address walreceiver by procno, not direct pointer to
 its latch

---
 src/backend/access/transam/xlogfuncs.c        |  1 +
 .../libpqwalreceiver/libpqwalreceiver.c       |  1 +
 src/backend/replication/walreceiver.c         | 17 ++++++-------
 src/backend/replication/walreceiverfuncs.c    | 12 ++++++----
 src/include/replication/walreceiver.h         | 24 +++++++++----------
 5 files changed, 29 insertions(+), 26 deletions(-)

diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 4e46baaebd..b0c6d7c687 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -28,6 +28,7 @@
 #include "pgstat.h"
 #include "replication/walreceiver.h"
 #include "storage/fd.h"
+#include "storage/latch.h"
 #include "storage/standby.h"
 #include "utils/builtins.h"
 #include "utils/memutils.h"
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 97f957cd87..c74369953f 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -30,6 +30,7 @@
 #include "pgstat.h"
 #include "pqexpbuffer.h"
 #include "replication/walreceiver.h"
+#include "storage/latch.h"
 #include "utils/builtins.h"
 #include "utils/memutils.h"
 #include "utils/pg_lsn.h"
diff --git a/src/backend/replication/walreceiver.c b/src/backend/replication/walreceiver.c
index a27aee63de..d1d99de980 100644
--- a/src/backend/replication/walreceiver.c
+++ b/src/backend/replication/walreceiver.c
@@ -266,8 +266,8 @@ WalReceiverMain(char *startup_data, size_t startup_data_len)
 	walrcv->lastMsgSendTime =
 		walrcv->lastMsgReceiptTime = walrcv->latestWalEndTime = now;
 
-	/* Report the latch to use to awaken this process */
-	walrcv->latch = &MyProc->procLatch;
+	/* Report our PGPROC entry to use to awaken this process */
+	walrcv->procno = MyProcNumber;
 
 	SpinLockRelease(&walrcv->mutex);
 
@@ -819,8 +819,8 @@ WalRcvDie(int code, Datum arg)
 	Assert(walrcv->pid == MyProcPid);
 	walrcv->walRcvState = WALRCV_STOPPED;
 	walrcv->pid = 0;
+	walrcv->procno = INVALID_PROC_NUMBER;
 	walrcv->ready_to_display = false;
-	walrcv->latch = NULL;
 	SpinLockRelease(&walrcv->mutex);
 
 	ConditionVariableBroadcast(&walrcv->walRcvStoppedCV);
@@ -1358,15 +1358,16 @@ WalRcvComputeNextWakeup(WalRcvWakeupReason reason, TimestampTz now)
 void
 WalRcvForceReply(void)
 {
-	Latch	   *latch;
+	ProcNumber	procno;
 
 	WalRcv->force_reply = true;
-	/* fetching the latch pointer might not be atomic, so use spinlock */
+
+	/* fetching the proc number is probably atomic, but don't rely on it */
 	SpinLockAcquire(&WalRcv->mutex);
-	latch = WalRcv->latch;
+	procno = WalRcv->procno;
 	SpinLockRelease(&WalRcv->mutex);
-	if (latch)
-		SetLatch(latch);
+	if (procno != INVALID_PROC_NUMBER)
+		SetLatch(&GetPGProcByNumber(procno)->procLatch);
 }
 
 /*
diff --git a/src/backend/replication/walreceiverfuncs.c b/src/backend/replication/walreceiverfuncs.c
index 85a19cdfa5..b1780d0106 100644
--- a/src/backend/replication/walreceiverfuncs.c
+++ b/src/backend/replication/walreceiverfuncs.c
@@ -26,7 +26,9 @@
 #include "access/xlogrecovery.h"
 #include "pgstat.h"
 #include "replication/walreceiver.h"
+#include "storage/latch.h"
 #include "storage/pmsignal.h"
+#include "storage/proc.h"
 #include "storage/shmem.h"
 #include "utils/timestamp.h"
 
@@ -66,7 +68,7 @@ WalRcvShmemInit(void)
 		ConditionVariableInit(&WalRcv->walRcvStoppedCV);
 		SpinLockInit(&WalRcv->mutex);
 		pg_atomic_init_u64(&WalRcv->writtenUpto, 0);
-		WalRcv->latch = NULL;
+		WalRcv->procno = INVALID_PROC_NUMBER;
 	}
 }
 
@@ -248,7 +250,7 @@ RequestXLogStreaming(TimeLineID tli, XLogRecPtr recptr, const char *conninfo,
 	WalRcvData *walrcv = WalRcv;
 	bool		launch = false;
 	pg_time_t	now = (pg_time_t) time(NULL);
-	Latch	   *latch;
+	ProcNumber	walrcv_proc;
 
 	/*
 	 * We always start at the beginning of the segment. That prevents a broken
@@ -309,14 +311,14 @@ RequestXLogStreaming(TimeLineID tli, XLogRecPtr recptr, const char *conninfo,
 	walrcv->receiveStart = recptr;
 	walrcv->receiveStartTLI = tli;
 
-	latch = walrcv->latch;
+	walrcv_proc = walrcv->procno;
 
 	SpinLockRelease(&walrcv->mutex);
 
 	if (launch)
 		SendPostmasterSignal(PMSIGNAL_START_WALRECEIVER);
-	else if (latch)
-		SetLatch(latch);
+	else if (walrcv_proc != INVALID_PROC_NUMBER)
+		SetLatch(&GetPGProcByNumber(walrcv_proc)->procLatch);
 }
 
 /*
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 132e789948..f86e4cda4c 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -21,7 +21,6 @@
 #include "replication/logicalproto.h"
 #include "replication/walsender.h"
 #include "storage/condition_variable.h"
-#include "storage/latch.h"
 #include "storage/spin.h"
 #include "utils/tuplestore.h"
 
@@ -58,11 +57,19 @@ typedef enum
 typedef struct
 {
 	/*
-	 * PID of currently active walreceiver process, its current state and
-	 * start time (actually, the time at which it was requested to be
-	 * started).
+	 * Proc number of currently active walreceiver process, so that the
+	 * startup process can wake it up after telling it where to start
+	 * streaming (after setting receiveStart and receiveStartTLI), and also to
+	 * tell it to send apply feedback to the primary whenever specially marked
+	 * commit records are applied.
 	 */
+	ProcNumber	procno;
 	pid_t		pid;
+
+	/*
+	 * Its current state and start time (actually, the time at which it was
+	 * requested to be started).
+	 */
 	WalRcvState walRcvState;
 	ConditionVariable walRcvStoppedCV;
 	pg_time_t	startTime;
@@ -134,15 +141,6 @@ typedef struct
 	/* set true once conninfo is ready to display (obfuscated pwds etc) */
 	bool		ready_to_display;
 
-	/*
-	 * Latch used by startup process to wake up walreceiver after telling it
-	 * where to start streaming (after setting receiveStart and
-	 * receiveStartTLI), and also to tell it to send apply feedback to the
-	 * primary whenever specially marked commit records are applied. This is
-	 * normally mapped to procLatch when walreceiver is running.
-	 */
-	Latch	   *latch;
-
 	slock_t		mutex;			/* locks shared variables shown above */
 
 	/*
-- 
2.39.2