PostgreSQL locks

lock.c

/*
 * Data structures defining the semantics of the standard lock methods.
 *
 * The conflict table defines the semantics of the various lock modes.
 */
static const LOCKMASK LockConflicts[] = {
	0,

	/* AccessShareLock */
	LOCKBIT_ON(AccessExclusiveLock),

	/* RowShareLock */
	LOCKBIT_ON(ExclusiveLock) | LOCKBIT_ON(AccessExclusiveLock),

	/* RowExclusiveLock */
	LOCKBIT_ON(ShareLock) | LOCKBIT_ON(ShareRowExclusiveLock) |
	LOCKBIT_ON(ExclusiveLock) | LOCKBIT_ON(AccessExclusiveLock),

	/* ShareUpdateExclusiveLock */
	LOCKBIT_ON(ShareUpdateExclusiveLock) |
	LOCKBIT_ON(ShareLock) | LOCKBIT_ON(ShareRowExclusiveLock) |
	LOCKBIT_ON(ExclusiveLock) | LOCKBIT_ON(AccessExclusiveLock),

	/* ShareLock */
	LOCKBIT_ON(RowExclusiveLock) | LOCKBIT_ON(ShareUpdateExclusiveLock) |
	LOCKBIT_ON(ShareRowExclusiveLock) |
	LOCKBIT_ON(ExclusiveLock) | LOCKBIT_ON(AccessExclusiveLock),

	/* ShareRowExclusiveLock */
	LOCKBIT_ON(RowExclusiveLock) | LOCKBIT_ON(ShareUpdateExclusiveLock) |
	LOCKBIT_ON(ShareLock) | LOCKBIT_ON(ShareRowExclusiveLock) |
	LOCKBIT_ON(ExclusiveLock) | LOCKBIT_ON(AccessExclusiveLock),

	/* ExclusiveLock */
	LOCKBIT_ON(RowShareLock) |
	LOCKBIT_ON(RowExclusiveLock) | LOCKBIT_ON(ShareUpdateExclusiveLock) |
	LOCKBIT_ON(ShareLock) | LOCKBIT_ON(ShareRowExclusiveLock) |
	LOCKBIT_ON(ExclusiveLock) | LOCKBIT_ON(AccessExclusiveLock),

	/* AccessExclusiveLock */
	LOCKBIT_ON(AccessShareLock) | LOCKBIT_ON(RowShareLock) |
	LOCKBIT_ON(RowExclusiveLock) | LOCKBIT_ON(ShareUpdateExclusiveLock) |
	LOCKBIT_ON(ShareLock) | LOCKBIT_ON(ShareRowExclusiveLock) |
	LOCKBIT_ON(ExclusiveLock) | LOCKBIT_ON(AccessExclusiveLock)

};

lockdefs.h

/*
 * LOCKMODE is an integer (1..N) indicating a lock type.  LOCKMASK is a bit
 * mask indicating a set of held or requested lock types (the bit 1<<mode
 * corresponds to a particular lock mode).
 */
typedef int LOCKMASK;
typedef int LOCKMODE;

/*
 * These are the valid values of type LOCKMODE for all the standard lock
 * methods (both DEFAULT and USER).
 */

/* NoLock is not a lock mode, but a flag value meaning "don't get a lock" */
#define NoLock					0

#define AccessShareLock			1	/* SELECT */
#define RowShareLock			2	/* SELECT FOR UPDATE/FOR SHARE */
#define RowExclusiveLock		3	/* INSERT, UPDATE, DELETE */
#define ShareUpdateExclusiveLock 4	/* VACUUM (non-FULL),ANALYZE, CREATE INDEX
									 * CONCURRENTLY */
#define ShareLock				5	/* CREATE INDEX (WITHOUT CONCURRENTLY) */
#define ShareRowExclusiveLock	6	/* like EXCLUSIVE MODE, but allows ROW
									 * SHARE */
#define ExclusiveLock			7	/* blocks ROW SHARE/SELECT...FOR UPDATE */
#define AccessExclusiveLock		8	/* ALTER TABLE, DROP TABLE, VACUUM FULL,
									 * and unqualified LOCK TABLE */

#define MaxLockMode				8