WaitOnLock(LOCKTAB*ltable,LockTableIdtableId,LOCK*lock,

staticintWaitOnLock(LOCKTAB*ltable,LockTableIdtableId,LOCK*lock,

LOCKTlockt);

UnlockLockTable();

elog(NOTICE,"Timeout -- possible deadlock");

elog(NOTICE,"Timeout interval reached -- possible deadlock.");

elog(NOTICE,"See the lock(l) manual page for a possible cause.");

return;

}

externvoidProcQueueInit(PROC_QUEUE*queue);

ProcSleep(PROC_QUEUE*queue,SPINLOCKspinlock,inttoken,

externintProcSleep(PROC_QUEUE*queue,SPINLOCKspinlock,inttoken,

intprio,LOCK*lock);

externintProcLockWakeup(PROC_QUEUE*queue,char*ltable,char*lock);

externvoidProcAddLock(SHM_QUEUE*elem);

lock - exclusive lock a table

.nf

\fBlock\fR classname

.fi

.BR lock

exclusive locks a table inside a transaction. The classic use for this

is the case where you want to\fBselect\fP some data, then update it

inside a transaction. If you don't exclusive lock the table before the

\fBselect\fP, some other user may also read the selected data, and try

and do their own\fBupdate\fP, causing a deadlock while you both wait

for the other to release the\fBselect\fP-induced shared lock so you can

get an exclusive lock to do the\fBupdate.\fP

.nf

--

-- Proper locking to prevent deadlock

--

begin work;

lock mytable;

select * from mytable;

update mytable set (x = 100);

end work;

begin(l),

end(l),

select(l).