[CF 6009] v2 - make LWLockCounter a global variable

This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/6009

The branch will be overwritten each time a new patch version is posted to
the thread, and also periodically to check for bitrot caused by changes
on the master branch.

Patch(es): https://www.postgresql.org/message-id/aLG8jlpEZAseM-wk@nathan
Author(s): Nathan Bossart

Author: Commitfest Bot

src/backend/postmaster/launch_backend.c

@@ -102,6 +102,7 @@ typedef struct
 #endif
 	int			NamedLWLockTrancheRequests;
 	NamedLWLockTranche *NamedLWLockTrancheArray;
+	int		   *LWLockCounter;
 	LWLockPadded *MainLWLockArray;
 	slock_t    *ProcStructLock;
 	PROC_HDR   *ProcGlobal;
@@ -761,6 +762,7 @@ save_backend_variables(BackendParameters *param,
 
 	param->NamedLWLockTrancheRequests = NamedLWLockTrancheRequests;
 	param->NamedLWLockTrancheArray = NamedLWLockTrancheArray;
+	param->LWLockCounter = LWLockCounter;
 	param->MainLWLockArray = MainLWLockArray;
 	param->ProcStructLock = ProcStructLock;
 	param->ProcGlobal = ProcGlobal;
@@ -1021,6 +1023,7 @@ restore_backend_variables(BackendParameters *param)
 
 	NamedLWLockTrancheRequests = param->NamedLWLockTrancheRequests;
 	NamedLWLockTrancheArray = param->NamedLWLockTrancheArray;
+	LWLockCounter = param->LWLockCounter;
 	MainLWLockArray = param->MainLWLockArray;
 	ProcStructLock = param->ProcStructLock;
 	ProcGlobal = param->ProcGlobal;

src/backend/storage/lmgr/lwlock.c

@@ -196,6 +196,7 @@ int			NamedLWLockTrancheRequests = 0;
 
 /* points to data in shared memory: */
 NamedLWLockTranche *NamedLWLockTrancheArray = NULL;
+int		   *LWLockCounter = NULL;
 
 static void InitializeLWLocks(void);
 static inline void LWLockReportWaitStart(LWLock *lock);
@@ -397,11 +398,11 @@ LWLockShmemSize(void)
 	/* Calculate total number of locks needed in the main array. */
 	numLocks += NumLWLocksForNamedTranches();
 
-	/* Space for the LWLock array. */
-	size = mul_size(numLocks, sizeof(LWLockPadded));
-
 	/* Space for dynamic allocation counter, plus room for alignment. */
-	size = add_size(size, sizeof(int) + LWLOCK_PADDED_SIZE);
+	size = sizeof(int) + LWLOCK_PADDED_SIZE;
+
+	/* Space for the LWLock array. */
+	size = add_size(size, mul_size(numLocks, sizeof(LWLockPadded)));
 
 	/* space for named tranches. */
 	size = add_size(size, mul_size(NamedLWLockTrancheRequests, sizeof(NamedLWLockTranche)));
@@ -423,27 +424,20 @@ CreateLWLocks(void)
 	if (!IsUnderPostmaster)
 	{
 		Size		spaceLocks = LWLockShmemSize();
-		int		   *LWLockCounter;
 		char	   *ptr;
 
 		/* Allocate space */
 		ptr = (char *) ShmemAlloc(spaceLocks);
 
-		/* Leave room for dynamic allocation of tranches */
+		/* Initialize the dynamic-allocation counter for tranches */
+		LWLockCounter = (int *) ptr;
+		*LWLockCounter = LWTRANCHE_FIRST_USER_DEFINED;
 		ptr += sizeof(int);
 
 		/* Ensure desired alignment of LWLock array */
 		ptr += LWLOCK_PADDED_SIZE - ((uintptr_t) ptr) % LWLOCK_PADDED_SIZE;
-
 		MainLWLockArray = (LWLockPadded *) ptr;
 
-		/*
-		 * Initialize the dynamic-allocation counter for tranches, which is
-		 * stored just before the first LWLock.
-		 */
-		LWLockCounter = (int *) ((char *) MainLWLockArray - sizeof(int));
-		*LWLockCounter = LWTRANCHE_FIRST_USER_DEFINED;
-
 		/* Initialize all LWLocks */
 		InitializeLWLocks();
 	}
@@ -574,9 +568,7 @@ int
 LWLockNewTrancheId(void)
 {
 	int			result;
-	int		   *LWLockCounter;
 
-	LWLockCounter = (int *) ((char *) MainLWLockArray - sizeof(int));
 	/* We use the ShmemLock spinlock to protect LWLockCounter */
 	SpinLockAcquire(ShmemLock);
 	result = (*LWLockCounter)++;

src/include/storage/lwlock.h

@@ -82,6 +82,7 @@ typedef struct NamedLWLockTranche
 
 extern PGDLLIMPORT NamedLWLockTranche *NamedLWLockTrancheArray;
 extern PGDLLIMPORT int NamedLWLockTrancheRequests;
+extern PGDLLIMPORT int *LWLockCounter;
 
 /*
  * It's a bit odd to declare NUM_BUFFER_PARTITIONS and NUM_LOCK_PARTITIONS