Function SetupLockInTable

src/backend/storage/lmgr/lock.c:1354–1540

* Find or create LOCK and PROCLOCK objects as needed for a new lock * request. * * Returns the PROCLOCK object, or NULL if we failed to create the objects * for lack of shared memory. * * The appropriate partition lock must be held at entry, and will be * held at exit. */

 * held at exit.
 */
static PROCLOCK *
SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc,
				 const LOCKTAG *locktag, uint32 hashcode, LOCKMODE lockmode)
{
	LOCK	   *lock;
	PROCLOCK   *proclock;
	PROCLOCKTAG proclocktag;
	uint32		proclock_hashcode;
	bool		found;

	/*
	 * Find or create a lock with this tag.
	 */
	lock = (LOCK *) hash_search_with_hash_value(LockMethodLockHash,
												(const void *) locktag,
												hashcode,
												HASH_ENTER_NULL,
												&found);
	if (!lock)
		return NULL;

	/*
	 * if it's a new lock object, initialize it
	 */
	if (!found)
	{
		lock->grantMask = 0;
		lock->waitMask = 0;
		SHMQueueInit(&(lock->procLocks));
		ProcQueueInit(&(lock->waitProcs));
		lock->nRequested = 0;
		lock->nGranted = 0;
		MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES);
		MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES);
		/*
		 * By default, holdTillEndXact is true only for LOCKTAG_TRANSACTION
		 */
		lock->holdTillEndXact = locktag->locktag_type == LOCKTAG_TRANSACTION;
		LOCK_PRINT("LockAcquire: new", lock, lockmode);
	}
	else
	{
		LOCK_PRINT("LockAcquire: found", lock, lockmode);
		Assert((lock->nRequested >= 0) && (lock->requested[lockmode] >= 0));
		Assert((lock->nGranted >= 0) && (lock->granted[lockmode] >= 0));
		Assert(lock->nGranted <= lock->nRequested);
	}

	/*
	 * holdTillEndXact must be true for LOCKTAG_TRANSACTION and
	 * false for LOCKTAG_RELATION_EXTEND no matter if it is a new lock or
	 * an existing lock
	 */
	AssertImply(locktag->locktag_type == LOCKTAG_TRANSACTION,
				lock->holdTillEndXact);
	AssertImply(locktag->locktag_type == LOCKTAG_RELATION_EXTEND,
				!(lock->holdTillEndXact));