Return ReplicationSlotAcquire API to its original form

Per 96540f80; the awkward API introduced by c6550776 is no
longer needed.

Author: Andres Freund <andres@anarazel.de>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/20210408020913.zzprrlvqyvlt5cyy@alap3.anarazel.de

src/backend/replication/logical/logicalfuncs.c

@@ -225,7 +225,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 	else
 		end_of_wal = GetXLogReplayRecPtr(&ThisTimeLineID);
 
-	(void) ReplicationSlotAcquire(NameStr(*name), SAB_Error);
+	ReplicationSlotAcquire(NameStr(*name), true);
 
 	PG_TRY();
 	{

src/backend/replication/slot.c

@@ -99,8 +99,6 @@ ReplicationSlot *MyReplicationSlot = NULL;
 int			max_replication_slots = 0;	/* the maximum number of replication
 										 * slots */
 
-static int	ReplicationSlotAcquireInternal(ReplicationSlot *slot,
-										   const char *name, SlotAcquireBehavior behavior);
 static void ReplicationSlotDropAcquired(void);
 static void ReplicationSlotDropPtr(ReplicationSlot *slot);
 
@@ -374,34 +372,16 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 /*
  * Find a previously created slot and mark it as used by this process.
  *
- * The return value is only useful if behavior is SAB_Inquire, in which
- * it's zero if we successfully acquired the slot, -1 if the slot no longer
- * exists, or the PID of the owning process otherwise.  If behavior is
- * SAB_Error, then trying to acquire an owned slot is an error.
- * If SAB_Block, we sleep until the slot is released by the owning process.
+ * An error is raised if nowait is true and the slot is currently in use. If
+ * nowait is false, we sleep until the slot is released by the owning process.
  */
-int
-ReplicationSlotAcquire(const char *name, SlotAcquireBehavior behavior)
-{
-	return ReplicationSlotAcquireInternal(NULL, name, behavior);
-}
-
-/*
- * Mark the specified slot as used by this process.
- *
- * Only one of slot and name can be specified.
- * If slot == NULL, search for the slot with the given name.
- *
- * See comments about the return value in ReplicationSlotAcquire().
- */
-static int
-ReplicationSlotAcquireInternal(ReplicationSlot *slot, const char *name,
-							   SlotAcquireBehavior behavior)
+void
+ReplicationSlotAcquire(const char *name, bool nowait)
 {
 	ReplicationSlot *s;
 	int			active_pid;
 
-	AssertArg((slot == NULL) ^ (name == NULL));
+	AssertArg(name != NULL);
 
 retry:
 	Assert(MyReplicationSlot == NULL);
@@ -412,17 +392,15 @@ retry:
 	 * Search for the slot with the specified name if the slot to acquire is
 	 * not given. If the slot is not found, we either return -1 or error out.
 	 */
-	s = slot ? slot : SearchNamedReplicationSlot(name, false);
+	s = SearchNamedReplicationSlot(name, false);
 	if (s == NULL || !s->in_use)
 	{
 		LWLockRelease(ReplicationSlotControlLock);
 
-		if (behavior == SAB_Inquire)
-			return -1;
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_OBJECT),
 				 errmsg("replication slot \"%s\" does not exist",
-						name ? name : NameStr(slot->data.name))));
+						name)));
 	}
 
 	/*
@@ -436,7 +414,7 @@ retry:
 		 * (We may end up not sleeping, but we don't want to do this while
 		 * holding the spinlock.)
 		 */
-		if (behavior == SAB_Block)
+		if (!nowait)
 			ConditionVariablePrepareToSleep(&s->active_cv);
 
 		SpinLockAcquire(&s->mutex);
@@ -456,13 +434,11 @@ retry:
 	 */
 	if (active_pid != MyProcPid)
 	{
-		if (behavior == SAB_Error)
+		if (!nowait)
 			ereport(ERROR,
 					(errcode(ERRCODE_OBJECT_IN_USE),
 					 errmsg("replication slot \"%s\" is active for PID %d",
 							NameStr(s->data.name), active_pid)));
-		else if (behavior == SAB_Inquire)
-			return active_pid;
 
 		/* Wait here until we get signaled, and then restart */
 		ConditionVariableSleep(&s->active_cv,
@@ -470,7 +446,7 @@ retry:
 		ConditionVariableCancelSleep();
 		goto retry;
 	}
-	else if (behavior == SAB_Block)
+	else if (!nowait)
 		ConditionVariableCancelSleep(); /* no sleep needed after all */
 
 	/* Let everybody know we've modified this slot */
@@ -478,9 +454,6 @@ retry:
 
 	/* We made this slot active, so it's ours now. */
 	MyReplicationSlot = s;
-
-	/* success */
-	return 0;
 }
 
 /*
@@ -588,7 +561,7 @@ ReplicationSlotDrop(const char *name, bool nowait)
 {
 	Assert(MyReplicationSlot == NULL);
 
-	(void) ReplicationSlotAcquire(name, nowait ? SAB_Error : SAB_Block);
+	ReplicationSlotAcquire(name, nowait);
 
 	ReplicationSlotDropAcquired();
 }
@@ -1271,8 +1244,8 @@ InvalidatePossiblyObsoleteSlot(ReplicationSlot *s, XLogRecPtr oldestLSN)
 								   WAIT_EVENT_REPLICATION_SLOT_DROP);
 
 			/*
-			 * Re-acquire lock and start over; we expect to invalidate the slot
-			 * next time (unless another process acquires the slot in the
+			 * Re-acquire lock and start over; we expect to invalidate the
+			 * slot next time (unless another process acquires the slot in the
 			 * meantime).
 			 */
 			LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);

src/backend/replication/slotfuncs.c

@@ -639,7 +639,7 @@ pg_replication_slot_advance(PG_FUNCTION_ARGS)
 		moveto = Min(moveto, GetXLogReplayRecPtr(&ThisTimeLineID));
 
 	/* Acquire the slot so we "own" it */
-	(void) ReplicationSlotAcquire(NameStr(*slotname), SAB_Error);
+	ReplicationSlotAcquire(NameStr(*slotname), true);
 
 	/* A slot whose restart_lsn has never been reserved cannot be advanced */
 	if (XLogRecPtrIsInvalid(MyReplicationSlot->data.restart_lsn))

src/backend/replication/walsender.c

@@ -601,7 +601,7 @@ StartReplication(StartReplicationCmd *cmd)
 
 	if (cmd->slotname)
 	{
-		(void) ReplicationSlotAcquire(cmd->slotname, SAB_Error);
+		ReplicationSlotAcquire(cmd->slotname, true);
 		if (SlotIsLogical(MyReplicationSlot))
 			ereport(ERROR,
 					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
@@ -1137,7 +1137,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 
 	Assert(!MyReplicationSlot);
 
-	(void) ReplicationSlotAcquire(cmd->slotname, SAB_Error);
+	ReplicationSlotAcquire(cmd->slotname, true);
 
 	if (XLogRecPtrIsInvalid(MyReplicationSlot->data.restart_lsn))
 		ereport(ERROR,

src/include/replication/slot.h

@@ -37,14 +37,6 @@ typedef enum ReplicationSlotPersistency
 	RS_TEMPORARY
 } ReplicationSlotPersistency;
 
-/* For ReplicationSlotAcquire, q.v. */
-typedef enum SlotAcquireBehavior
-{
-	SAB_Error,
-	SAB_Block,
-	SAB_Inquire
-} SlotAcquireBehavior;
-
 /*
  * On-Disk data of a replication slot, preserved across restarts.
  */
@@ -208,7 +200,7 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 
-extern int	ReplicationSlotAcquire(const char *name, SlotAcquireBehavior behavior);
+extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
 extern void ReplicationSlotCleanup(void);
 extern void ReplicationSlotSave(void);