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Commit15ad6f1

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When building with LWLOCK_STATS, initialize the stats in LWLockWaitUntilFree.
If LWLockWaitUntilFree was called before the first LWLockAcquire call, youwould either crash because of access to uninitialized array or account theacquisition incorrectly. LWLockConditionalAcquire doesn't have this problembecause it doesn't update the lwlock stats.In practice, this never happens because there is no codepath where you wouldcall LWLockWaitUntilfree before LWLockAcquire after a new process islaunched. But that's just accidental, there's no guarantee that that'salways going to be true in the future.Spotted by Jeff Janes.
1 parent442231d commit15ad6f1

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1 file changed

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‎src/backend/storage/lmgr/lwlock.c

Lines changed: 23 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -123,6 +123,22 @@ LOG_LWDEBUG(const char *where, LWLockId lockid, const char *msg)
123123

124124
#ifdefLWLOCK_STATS
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126+
staticvoidinit_lwlock_stats(void);
127+
staticvoidprint_lwlock_stats(intcode,Datumarg);
128+
129+
staticvoid
130+
init_lwlock_stats(void)
131+
{
132+
int*LWLockCounter= (int*) ((char*)LWLockArray-2*sizeof(int));
133+
intnumLocks=LWLockCounter[1];
134+
135+
sh_acquire_counts=calloc(numLocks,sizeof(int));
136+
ex_acquire_counts=calloc(numLocks,sizeof(int));
137+
block_counts=calloc(numLocks,sizeof(int));
138+
counts_for_pid=MyProcPid;
139+
on_shmem_exit(print_lwlock_stats,0);
140+
}
141+
126142
staticvoid
127143
print_lwlock_stats(intcode,Datumarg)
128144
{
@@ -332,16 +348,7 @@ LWLockAcquire(LWLockId lockid, LWLockMode mode)
332348
#ifdefLWLOCK_STATS
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/* Set up local count state first time through in a given process */
334350
if (counts_for_pid!=MyProcPid)
335-
{
336-
int*LWLockCounter= (int*) ((char*)LWLockArray-2*sizeof(int));
337-
intnumLocks=LWLockCounter[1];
338-
339-
sh_acquire_counts=calloc(numLocks,sizeof(int));
340-
ex_acquire_counts=calloc(numLocks,sizeof(int));
341-
block_counts=calloc(numLocks,sizeof(int));
342-
counts_for_pid=MyProcPid;
343-
on_shmem_exit(print_lwlock_stats,0);
344-
}
351+
init_lwlock_stats();
345352
/* Count lock acquisition attempts */
346353
if (mode==LW_EXCLUSIVE)
347354
ex_acquire_counts[lockid]++;
@@ -588,6 +595,12 @@ LWLockWaitUntilFree(LWLockId lockid, LWLockMode mode)
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589596
PRINT_LWDEBUG("LWLockWaitUntilFree",lockid,lock);
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598+
#ifdefLWLOCK_STATS
599+
/* Set up local count state first time through in a given process */
600+
if (counts_for_pid!=MyProcPid)
601+
init_lwlock_stats();
602+
#endif
603+
591604
/* Ensure we will have room to remember the lock */
592605
if (num_held_lwlocks >=MAX_SIMUL_LWLOCKS)
593606
elog(ERROR,"too many LWLocks taken");

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