Code cleanup in the wake of recent LWLock refactoring.

As of commit c1772ad, there's no
longer any way of requesting additional LWLocks in the main tranche,
so we don't need NumLWLocks() or LWLockAssign() any more.  Also,
some of the allocation counters that we had previously aren't needed
any more either.

Amit Kapila

Author: robertmhaas

src/backend/storage/lmgr/lwlock.c

@@ -91,7 +91,7 @@
 #endif
 
 
-/* We use the ShmemLock spinlock to protect LWLockAssign */
+/* We use the ShmemLock spinlock to protect LWLockCounter */
 extern slock_t *ShmemLock;
 
 #define LW_FLAG_HAS_WAITERS			((uint32) 1 << 30)
@@ -363,30 +363,6 @@ NumLWLocksByNamedTranches(void)
 	return numLocks;
 }
 
-/*
- * Compute number of LWLocks to allocate in the main array.
- */
-static int
-NumLWLocks(void)
-{
-	int			numLocks;
-
-	/*
-	 * Many users of LWLocks no longer reserve space in the main array here,
-	 * but instead allocate separate tranches.  The latter approach has the
-	 * advantage of allowing LWLOCK_STATS and LOCK_DEBUG output to produce
-	 * more useful output.
-	 */
-
-	/* Predefined LWLocks */
-	numLocks = NUM_FIXED_LWLOCKS;
-
-	/* Disallow named LWLocks' requests after startup */
-	lock_named_request_allowed = false;
-
-	return numLocks;
-}
-
 /*
  * Compute shmem space needed for LWLocks and named tranches.
  */
@@ -395,15 +371,15 @@ LWLockShmemSize(void)
 {
 	Size		size;
 	int			i;
-	int			numLocks = NumLWLocks();
+	int			numLocks = NUM_FIXED_LWLOCKS;
 
 	numLocks += NumLWLocksByNamedTranches();
 
 	/* Space for the LWLock array. */
 	size = mul_size(numLocks, sizeof(LWLockPadded));
 
 	/* Space for dynamic allocation counter, plus room for alignment. */
-	size = add_size(size, 3 * sizeof(int) + LWLOCK_PADDED_SIZE);
+	size = add_size(size, sizeof(int) + LWLOCK_PADDED_SIZE);
 
 	/* space for named tranches. */
 	size = add_size(size, mul_size(NamedLWLockTrancheRequests, sizeof(NamedLWLockTranche)));
@@ -412,6 +388,9 @@ LWLockShmemSize(void)
 	for (i = 0; i < NamedLWLockTrancheRequests; i++)
 		size = add_size(size, strlen(NamedLWLockTrancheRequestArray[i].tranche_name) + 1);
 
+	/* Disallow named LWLocks' requests after startup */
+	lock_named_request_allowed = false;
+
 	return size;
 }
 
@@ -433,7 +412,7 @@ CreateLWLocks(void)
 
 	if (!IsUnderPostmaster)
 	{
-		int			numLocks = NumLWLocks();
+		int			numLocks = NUM_FIXED_LWLOCKS;
 		int			numNamedLocks = NumLWLocksByNamedTranches();
 		Size		spaceLocks = LWLockShmemSize();
 		LWLockPadded *lock;
@@ -445,8 +424,8 @@ CreateLWLocks(void)
 		/* Allocate space */
 		ptr = (char *) ShmemAlloc(spaceLocks);
 
-		/* Leave room for dynamic allocation of locks and tranches */
-		ptr += 3 * sizeof(int);
+		/* Leave room for dynamic allocation of tranches */
+		ptr += sizeof(int);
 
 		/* Ensure desired alignment of LWLock array */
 		ptr += LWLOCK_PADDED_SIZE - ((uintptr_t) ptr) % LWLOCK_PADDED_SIZE;
@@ -458,16 +437,11 @@ CreateLWLocks(void)
 			LWLockInitialize(&lock->lock, LWTRANCHE_MAIN);
 
 		/*
-		 * Initialize the dynamic-allocation counters, which are stored just
-		 * before the first LWLock.  LWLockCounter[0] is the allocation
-		 * counter for lwlocks, LWLockCounter[1] is the maximum number that
-		 * can be allocated from the main array, and LWLockCounter[2] is the
-		 * allocation counter for tranches.
+		 * Initialize the dynamic-allocation counter for tranches, which is
+		 * stored just before the first LWLock.
 		 */
-		LWLockCounter = (int *) ((char *) MainLWLockArray - 3 * sizeof(int));
-		LWLockCounter[0] = NUM_FIXED_LWLOCKS;
-		LWLockCounter[1] = numLocks;
-		LWLockCounter[2] = LWTRANCHE_FIRST_USER_DEFINED;
+		LWLockCounter = (int *) ((char *) MainLWLockArray - sizeof(int));
+		*LWLockCounter = LWTRANCHE_FIRST_USER_DEFINED;
 
 		/* Initialize named tranches. */
 		if (NamedLWLockTrancheRequests > 0)
@@ -535,32 +509,6 @@ InitLWLockAccess(void)
 #endif
 }
 
-/*
- * LWLockAssign - assign a dynamically-allocated LWLock number
- *
- * We interlock this using the same spinlock that is used to protect
- * ShmemAlloc().  Interlocking is not really necessary during postmaster
- * startup, but it is needed if any user-defined code tries to allocate
- * LWLocks after startup.
- */
-LWLock *
-LWLockAssign(void)
-{
-	LWLock	   *result;
-	int		   *LWLockCounter;
-
-	LWLockCounter = (int *) ((char *) MainLWLockArray - 3 * sizeof(int));
-	SpinLockAcquire(ShmemLock);
-	if (LWLockCounter[0] >= LWLockCounter[1])
-	{
-		SpinLockRelease(ShmemLock);
-		elog(ERROR, "no more LWLocks available");
-	}
-	result = &MainLWLockArray[LWLockCounter[0]++].lock;
-	SpinLockRelease(ShmemLock);
-	return result;
-}
-
 /*
  * GetNamedLWLockTranche - returns the base address of LWLock from the
  *		specified tranche.
@@ -574,16 +522,13 @@ GetNamedLWLockTranche(const char *tranche_name)
 {
 	int			lock_pos;
 	int			i;
-	int		   *LWLockCounter;
-
-	LWLockCounter = (int *) ((char *) MainLWLockArray - 3 * sizeof(int));
 
 	/*
 	 * Obtain the position of base address of LWLock belonging to requested
 	 * tranche_name in MainLWLockArray.  LWLocks for named tranches are placed
-	 * in MainLWLockArray after LWLocks specified by LWLockCounter[1].
+	 * in MainLWLockArray after fixed locks.
 	 */
-	lock_pos = LWLockCounter[1];
+	lock_pos = NUM_FIXED_LWLOCKS;
 	for (i = 0; i < NamedLWLockTrancheRequests; i++)
 	{
 		if (strcmp(NamedLWLockTrancheRequestArray[i].tranche_name,
@@ -609,9 +554,9 @@ LWLockNewTrancheId(void)
 	int			result;
 	int		   *LWLockCounter;
 
-	LWLockCounter = (int *) ((char *) MainLWLockArray - 3 * sizeof(int));
+	LWLockCounter = (int *) ((char *) MainLWLockArray - sizeof(int));
 	SpinLockAcquire(ShmemLock);
-	result = LWLockCounter[2]++;
+	result = (*LWLockCounter)++;
 	SpinLockRelease(ShmemLock);
 
 	return result;

src/include/storage/lwlock.h

@@ -196,8 +196,6 @@ extern void InitLWLockAccess(void);
 extern void RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks);
 extern LWLockPadded *GetNamedLWLockTranche(const char *tranche_name);
 
-extern LWLock *LWLockAssign(void);
-
 /*
  * There is another, more flexible method of obtaining lwlocks. First, call
  * LWLockNewTrancheId just once to obtain a tranche ID; this allocates from