Re: make LWLockCounter a global variable

Nathan Bossart <nathandbossart@gmail.com> writes:
> In lwlock.c, uses of LWLockCounter must first calculate its address in
> shared memory with something like this:

> 	LWLockCounter = (int *) ((char *) MainLWLockArray - sizeof(int));

> This appears to have been started by commit 82e861f in order to fix
> EXEC_BACKEND builds, but it could also be fixed by adding it to the
> BackendParameters struct.  I find the current approach somewhat difficult
> to read and understand, so I'd like to switch to the latter approach.  This
> is admittedly just nitpicking...

No objection here.  As a small improvement, perhaps you could swap
around the code in LWLockShmemSize so that the order in which it
considers size contributions matches the physical layout, more
or less like

	/* Calculate total number of locks needed in the main array. */
	numLocks += NumLWLocksForNamedTranches();

+	/* Space for dynamic allocation counter, plus room for alignment. */
+	size = sizeof(int) + LWLOCK_PADDED_SIZE;
+
	/* Space for the LWLock array. */
-	size = mul_size(numLocks, sizeof(LWLockPadded));
+	size = add_size(size, mul_size(numLocks, sizeof(LWLockPadded)));

-	/* Space for dynamic allocation counter, plus room for alignment. */
-	size = add_size(size, sizeof(int) + LWLOCK_PADDED_SIZE);
-
	/* space for named tranches. */
	size = add_size(size, mul_size(NamedLWLockTrancheRequests, sizeof(NamedLWLockTranche)));

I find it a little confusing that that code doesn't line up
exactly with what CreateLWLocks does.

			regards, tom lane