Use ProcNumbers instead of direct Latch pointers to address other procs

This is in preparation for replacing Latches with a new abstraction.
That's still work in progress, but this seems a little tidier anyway,
so let's get this refactoring out of the way already.

Discussion: https://www.postgresql.org/message-id/391abe21-413e-4d91-a650-b663af49500c%40iki.fi

3 files changed, 15 insertions, 13 deletions

diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 97f957cd87b..c74369953f8 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 a27aee63def..5f641d27905 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 proc number so that others can wake us up */
+	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 +1358,15 @@ 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 85a19cdfa5c..8557d10cf9d 100644
--- a/src/backend/replication/walreceiverfuncs.c
+++ b/src/backend/replication/walreceiverfuncs.c
@@ -27,6 +27,7 @@
 #include "pgstat.h"
 #include "replication/walreceiver.h"
 #include "storage/pmsignal.h"
+#include "storage/proc.h"
 #include "storage/shmem.h"
 #include "utils/timestamp.h"
 
@@ -66,7 +67,7 @@ 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 +249,7 @@ 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 +310,14 @@ 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);
 }
 
 /*