lock.h

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	 (locktag).locktag_lockmethodid = USER_LOCKMETHOD)


/*
 * Per-locked-object lock information:
 *
 * tag -- uniquely identifies the object being locked
 * grantMask -- bitmask for all lock types currently granted on this object.
 * waitMask -- bitmask for all lock types currently awaited on this object.
 * procLocks -- list of PROCLOCK objects for this lock.
 * waitProcs -- queue of processes waiting for this lock.
 * requested -- count of each lock type currently requested on the lock
 *		(includes requests already granted!!).
 * nRequested -- total requested locks of all types.
 * granted -- count of each lock type currently granted on the lock.
 * nGranted -- total granted locks of all types.
 *
 * Note: these counts count 1 for each backend.  Internally to a backend,
 * there may be multiple grabs on a particular lock, but this is not reflected
 * into shared memory.
 */
typedef struct LOCK
{
	/* hash key */
	LOCKTAG		tag;			/* unique identifier of lockable object */

	/* data */
	LOCKMASK	grantMask;		/* bitmask for lock types already granted */
	LOCKMASK	waitMask;		/* bitmask for lock types awaited */
	SHM_QUEUE	procLocks;		/* list of PROCLOCK objects assoc. with lock */
	PROC_QUEUE	waitProcs;		/* list of PGPROC objects waiting on lock */
	int			requested[MAX_LOCKMODES];		/* counts of requested locks */
	int			nRequested;		/* total of requested[] array */
	int			granted[MAX_LOCKMODES]; /* counts of granted locks */
	int			nGranted;		/* total of granted[] array */
} LOCK;

#define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid)


/*
 * We may have several different backends holding or awaiting locks
 * on the same lockable object.  We need to store some per-holder/waiter
 * information for each such holder (or would-be holder).  This is kept in
 * a PROCLOCK struct.
 *
 * PROCLOCKTAG is the key information needed to look up a PROCLOCK item in the
 * proclock hashtable.	A PROCLOCKTAG value uniquely identifies the combination
 * of a lockable object and a holder/waiter for that object.  (We can use
 * pointers here because the PROCLOCKTAG need only be unique for the lifespan
 * of the PROCLOCK, and it will never outlive the lock or the proc.)
 *
 * Internally to a backend, it is possible for the same lock to be held
 * for different purposes: the backend tracks transaction locks separately
 * from session locks.	However, this is not reflected in the shared-memory
 * state: we only track which backend(s) hold the lock.  This is OK since a
 * backend can never block itself.
 *
 * The holdMask field shows the already-granted locks represented by this
 * proclock.  Note that there will be a proclock object, possibly with
 * zero holdMask, for any lock that the process is currently waiting on.
 * Otherwise, proclock objects whose holdMasks are zero are recycled
 * as soon as convenient.
 *
 * releaseMask is workspace for LockReleaseAll(): it shows the locks due
 * to be released during the current call.	This must only be examined or
 * set by the backend owning the PROCLOCK.
 *
 * Each PROCLOCK object is linked into lists for both the associated LOCK
 * object and the owning PGPROC object.  Note that the PROCLOCK is entered
 * into these lists as soon as it is created, even if no lock has yet been
 * granted.  A PGPROC that is waiting for a lock to be granted will also be
 * linked into the lock's waitProcs queue.
 */
typedef struct PROCLOCKTAG
{
	/* NB: we assume this struct contains no padding! */
	LOCK	   *myLock;			/* link to per-lockable-object information */
	PGPROC	   *myProc;			/* link to PGPROC of owning backend */
} PROCLOCKTAG;

typedef struct PROCLOCK
{
	/* tag */
	PROCLOCKTAG tag;			/* unique identifier of proclock object */

	/* data */
	LOCKMASK	holdMask;		/* bitmask for lock types currently held */
	LOCKMASK	releaseMask;	/* bitmask for lock types to be released */
	SHM_QUEUE	lockLink;		/* list link in LOCK's list of proclocks */
	SHM_QUEUE	procLink;		/* list link in PGPROC's list of proclocks */
} PROCLOCK;

#define PROCLOCK_LOCKMETHOD(proclock) \
	LOCK_LOCKMETHOD(*((proclock).tag.myLock))

/*
 * Each backend also maintains a local hash table with information about each
 * lock it is currently interested in.	In particular the local table counts
 * the number of times that lock has been acquired.  This allows multiple
 * requests for the same lock to be executed without additional accesses to
 * shared memory.  We also track the number of lock acquisitions per
 * ResourceOwner, so that we can release just those locks belonging to a
 * particular ResourceOwner.
 */
typedef struct LOCALLOCKTAG
{
	LOCKTAG		lock;			/* identifies the lockable object */
	LOCKMODE	mode;			/* lock mode for this table entry */
} LOCALLOCKTAG;

typedef struct LOCALLOCKOWNER
{
	/*
	 * Note: if owner is NULL then the lock is held on behalf of the session;
	 * otherwise it is held on behalf of my current transaction.
	 *
	 * Must use a forward struct reference to avoid circularity.
	 */
	struct ResourceOwnerData *owner;
	int			nLocks;			/* # of times held by this owner */
} LOCALLOCKOWNER;

typedef struct LOCALLOCK
{
	/* tag */
	LOCALLOCKTAG tag;			/* unique identifier of locallock entry */

	/* data */
	LOCK	   *lock;			/* associated LOCK object in shared mem */
	PROCLOCK   *proclock;		/* associated PROCLOCK object in shmem */
	uint32		hashcode;		/* copy of LOCKTAG's hash value */
	int			nLocks;			/* total number of times lock is held */
	int			numLockOwners;	/* # of relevant ResourceOwners */
	int			maxLockOwners;	/* allocated size of array */
	LOCALLOCKOWNER *lockOwners; /* dynamically resizable array */
} LOCALLOCK;

#define LOCALLOCK_LOCKMETHOD(llock) ((llock).tag.lock.locktag_lockmethodid)


/*
 * This struct holds information passed from lmgr internals to the lock
 * listing user-level functions (in lockfuncs.c).	For each PROCLOCK in
 * the system, copies of the PROCLOCK object and associated PGPROC and
 * LOCK objects are stored.  Note there will often be multiple copies
 * of the same PGPROC or LOCK --- to detect whether two are the same,
 * compare the PROCLOCK tag fields.
 */
typedef struct LockData
{
	int			nelements;		/* The length of each of the arrays */
	PROCLOCK   *proclocks;
	PGPROC	   *procs;
	LOCK	   *locks;
} LockData;


/* Result codes for LockAcquire() */
typedef enum
{
	LOCKACQUIRE_NOT_AVAIL,		/* lock not available, and dontWait=true */
	LOCKACQUIRE_OK,				/* lock successfully acquired */
	LOCKACQUIRE_ALREADY_HELD	/* incremented count for lock already held */
} LockAcquireResult;


/*
 * The lockmgr's shared hash tables are partitioned to reduce contention.
 * To determine which partition a given locktag belongs to, compute the tag's
 * hash code with LockTagHashCode(), then apply one of these macros.
 * NB: NUM_LOCK_PARTITIONS must be a power of 2!
 */
#define LockHashPartition(hashcode) \
	((hashcode) % NUM_LOCK_PARTITIONS)
#define LockHashPartitionLock(hashcode) \
	((LWLockId) (FirstLockMgrLock + LockHashPartition(hashcode)))


/*
 * function prototypes
 */
extern void InitLocks(void);
extern LockMethod GetLocksMethodTable(const LOCK *lock);
extern uint32 LockTagHashCode(const LOCKTAG *locktag);
extern LockAcquireResult LockAcquire(const LOCKTAG *locktag,
			LOCKMODE lockmode,
			bool sessionLock,
			bool dontWait);
extern bool LockRelease(const LOCKTAG *locktag,
			LOCKMODE lockmode, bool sessionLock);
extern void LockReleaseAll(LOCKMETHODID lockmethodid, bool allLocks);
extern void LockReleaseCurrentOwner(void);
extern void LockReassignCurrentOwner(void);
extern List *GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode);
extern void AtPrepare_Locks(void);
extern void PostPrepare_Locks(TransactionId xid);
extern int LockCheckConflicts(LockMethod lockMethodTable,
				   LOCKMODE lockmode,
				   LOCK *lock, PROCLOCK *proclock, PGPROC *proc);
extern void GrantLock(LOCK *lock, PROCLOCK *proclock, LOCKMODE lockmode);
extern void GrantAwaitedLock(void);
extern void RemoveFromWaitQueue(PGPROC *proc, uint32 hashcode);
extern Size LockShmemSize(void);
extern LockData *GetLockStatusData(void);
extern const char *GetLockmodeName(LOCKMETHODID lockmethodid, LOCKMODE mode);

extern void lock_twophase_recover(TransactionId xid, uint16 info,
					  void *recdata, uint32 len);
extern void lock_twophase_postcommit(TransactionId xid, uint16 info,
						 void *recdata, uint32 len);
extern void lock_twophase_postabort(TransactionId xid, uint16 info,
						void *recdata, uint32 len);

extern bool DeadLockCheck(PGPROC *proc);
extern void DeadLockReport(void);
extern void RememberSimpleDeadLock(PGPROC *proc1,
					   LOCKMODE lockmode,
					   LOCK *lock,
					   PGPROC *proc2);
extern void InitDeadLockChecking(void);

#ifdef LOCK_DEBUG
extern void DumpLocks(PGPROC *proc);
extern void DumpAllLocks(void);
#endif

#endif   /* LOCK_H */