Re: Minor fix in lwlock.c

Actually, on further thought, there's a really simple solution that
we've used elsewhere: make sure you have the resource you need *before*
you get into the critical section of code.  I've applied the attached
revised patch.

            regards, tom lane

*** src/backend/storage/lmgr/lwlock.c.orig    Fri Dec 31 17:46:10 2004
--- src/backend/storage/lmgr/lwlock.c    Fri Apr  8 10:14:04 2005
***************
*** 213,218 ****
--- 213,222 ----
       */
      Assert(!(proc == NULL && IsUnderPostmaster));

+     /* Ensure we will have room to remember the lock */
+     if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
+         elog(ERROR, "too many LWLocks taken");
+
      /*
       * Lock out cancel/die interrupts until we exit the code section
       * protected by the LWLock.  This ensures that interrupts will not
***************
*** 328,334 ****
      SpinLockRelease_NoHoldoff(&lock->mutex);

      /* Add lock to list of locks held by this backend */
-     Assert(num_held_lwlocks < MAX_SIMUL_LWLOCKS);
      held_lwlocks[num_held_lwlocks++] = lockid;

      /*
--- 332,337 ----
***************
*** 353,358 ****
--- 356,365 ----

      PRINT_LWDEBUG("LWLockConditionalAcquire", lockid, lock);

+     /* Ensure we will have room to remember the lock */
+     if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
+         elog(ERROR, "too many LWLocks taken");
+
      /*
       * Lock out cancel/die interrupts until we exit the code section
       * protected by the LWLock.  This ensures that interrupts will not
***************
*** 397,403 ****
      else
      {
          /* Add lock to list of locks held by this backend */
-         Assert(num_held_lwlocks < MAX_SIMUL_LWLOCKS);
          held_lwlocks[num_held_lwlocks++] = lockid;
      }

--- 404,409 ----