Re: make LWLockCounter a global variable

Nathan Bossart <nathandbossart(at)gmail(dot)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