postgresql/src/include/storage/lock.h

/*-------------------------------------------------------------------------
 *
 * lock.h
 *	  POSTGRES low-level lock mechanism
 *
 *
 * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/include/storage/lock.h,v 1.97 2006/07/31 20:09:05 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef LOCK_H_
#define LOCK_H_

#include "storage/itemptr.h"
#include "storage/lwlock.h"
#include "storage/shmem.h"


/* struct PGPROC is declared in proc.h, but must forward-reference it */
typedef struct PGPROC PGPROC;

typedef struct PROC_QUEUE
{
	SHM_QUEUE	links;			/* head of list of PGPROC objects */
	int			size;			/* number of entries in list */
} PROC_QUEUE;

/* GUC variables */
extern int	max_locks_per_xact;

#ifdef LOCK_DEBUG
extern int	Trace_lock_oidmin;
extern bool Trace_locks;
extern bool Trace_userlocks;
extern int	Trace_lock_table;
extern bool Debug_deadlocks;
#endif   /* LOCK_DEBUG */


/*
 * 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;

/* MAX_LOCKMODES cannot be larger than the # of bits in LOCKMASK */
#define MAX_LOCKMODES		10

#define LOCKBIT_ON(lockmode) (1 << (lockmode))
#define LOCKBIT_OFF(lockmode) (~(1 << (lockmode)))


/*
 * This data structure defines the locking semantics associated with a
 * "lock method".  The semantics specify the meaning of each lock mode
 * (by defining which lock modes it conflicts with), and also whether locks
 * of this method are transactional (ie, are released at transaction end).
 * All of this data is constant and is kept in const tables.
 *
 * numLockModes -- number of lock modes (READ,WRITE,etc) that
 *		are defined in this lock method.  Must be less than MAX_LOCKMODES.
 *
 * transactional -- TRUE if locks are released automatically at xact end.
 *
 * conflictTab -- this is an array of bitmasks showing lock
 *		mode conflicts.  conflictTab[i] is a mask with the j-th bit
 *		turned on if lock modes i and j conflict.  Lock modes are
 *		numbered 1..numLockModes; conflictTab[0] is unused.
 *
 * lockModeNames -- ID strings for debug printouts.
 *
 * trace_flag -- pointer to GUC trace flag for this lock method.
 */
typedef struct LockMethodData
{
	int			numLockModes;
	bool		transactional;
	const LOCKMASK *conflictTab;
	const char * const *lockModeNames;
	const bool *trace_flag;
} LockMethodData;

typedef const LockMethodData *LockMethod;

/*
 * Lock methods are identified by LOCKMETHODID.  (Despite the declaration as
 * uint16, we are constrained to 256 lockmethods by the layout of LOCKTAG.)
 */
typedef uint16 LOCKMETHODID;

/* These identify the known lock methods */
#define DEFAULT_LOCKMETHOD	1
#define USER_LOCKMETHOD		2

/*
 * 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) */
#define ShareLock				5		/* CREATE INDEX */
#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 */


/*
 * LOCKTAG is the key information needed to look up a LOCK item in the
 * lock hashtable.	A LOCKTAG value uniquely identifies a lockable object.
 *
 * The LockTagType enum defines the different kinds of objects we can lock.
 * We can handle up to 256 different LockTagTypes.
 */
typedef enum LockTagType
{
	LOCKTAG_RELATION,			/* whole relation */
	/* ID info for a relation is DB OID + REL OID; DB OID = 0 if shared */
	LOCKTAG_RELATION_EXTEND,	/* the right to extend a relation */
	/* same ID info as RELATION */
	LOCKTAG_PAGE,				/* one page of a relation */
	/* ID info for a page is RELATION info + BlockNumber */
	LOCKTAG_TUPLE,				/* one physical tuple */
	/* ID info for a tuple is PAGE info + OffsetNumber */
	LOCKTAG_TRANSACTION,		/* transaction (for waiting for xact done) */
	/* ID info for a transaction is its TransactionId */
	LOCKTAG_OBJECT,				/* non-relation database object */
	/* ID info for an object is DB OID + CLASS OID + OBJECT OID + SUBID */

	/*
	 * Note: object ID has same representation as in pg_depend and
	 * pg_description, but notice that we are constraining SUBID to 16 bits.
	 * Also, we use DB OID = 0 for shared objects such as tablespaces.
	 */
	LOCKTAG_USERLOCK			/* reserved for contrib/userlock */
	/* ID info for a userlock is defined by user_locks.c */
} LockTagType;

/*
 * The LOCKTAG struct is defined with malice aforethought to fit into 16
 * bytes with no padding.  Note that this would need adjustment if we were
 * to widen Oid, BlockNumber, or TransactionId to more than 32 bits.
 *
 * We include lockmethodid in the locktag so that a single hash table in
 * shared memory can store locks of different lockmethods.
 */
typedef struct LOCKTAG
{
	uint32		locktag_field1; /* a 32-bit ID field */
	uint32		locktag_field2; /* a 32-bit ID field */
	uint32		locktag_field3; /* a 32-bit ID field */
	uint16		locktag_field4; /* a 16-bit ID field */
	uint8		locktag_type;	/* see enum LockTagType */
	uint8		locktag_lockmethodid;	/* lockmethod indicator */
} LOCKTAG;

/*
 * These macros define how we map logical IDs of lockable objects into
 * the physical fields of LOCKTAG.	Use these to set up LOCKTAG values,
 * rather than accessing the fields directly.  Note multiple eval of target!
 */
#define SET_LOCKTAG_RELATION(locktag,dboid,reloid) \
	((locktag).locktag_field1 = (dboid), \
	 (locktag).locktag_field2 = (reloid), \
	 (locktag).locktag_field3 = 0, \
	 (locktag).locktag_field4 = 0, \
	 (locktag).locktag_type = LOCKTAG_RELATION, \
	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)

#define SET_LOCKTAG_RELATION_EXTEND(locktag,dboid,reloid) \
	((locktag).locktag_field1 = (dboid), \
	 (locktag).locktag_field2 = (reloid), \
	 (locktag).locktag_field3 = 0, \
	 (locktag).locktag_field4 = 0, \
	 (locktag).locktag_type = LOCKTAG_RELATION_EXTEND, \
	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)

#define SET_LOCKTAG_PAGE(locktag,dboid,reloid,blocknum) \
	((locktag).locktag_field1 = (dboid), \
	 (locktag).locktag_field2 = (reloid), \
	 (locktag).locktag_field3 = (blocknum), \
	 (locktag).locktag_field4 = 0, \
	 (locktag).locktag_type = LOCKTAG_PAGE, \
	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)

#define SET_LOCKTAG_TUPLE(locktag,dboid,reloid,blocknum,offnum) \
	((locktag).locktag_field1 = (dboid), \
	 (locktag).locktag_field2 = (reloid), \
	 (locktag).locktag_field3 = (blocknum), \
	 (locktag).locktag_field4 = (offnum), \
	 (locktag).locktag_type = LOCKTAG_TUPLE, \
	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)

#define SET_LOCKTAG_TRANSACTION(locktag,xid) \
	((locktag).locktag_field1 = (xid), \
	 (locktag).locktag_field2 = 0, \
	 (locktag).locktag_field3 = 0, \
	 (locktag).locktag_field4 = 0, \
	 (locktag).locktag_type = LOCKTAG_TRANSACTION, \
	 (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD)

#define SET_LOCKTAG_OBJECT(locktag,dboid,classoid,objoid,objsubid) \
	((locktag).locktag_field1 = (dboid), \
	 (locktag).locktag_field2 = (classoid), \
	 (locktag).locktag_field3 = (objoid), \
	 (locktag).locktag_field4 = (objsubid), \
	 (locktag).locktag_type = LOCKTAG_OBJECT, \
	 (locktag).locktag_lockmethodid = DEFAULT_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 (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 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 bool DeadLockCheck(PGPROC *proc);
extern void DeadLockReport(void);
extern void RememberSimpleDeadLock(PGPROC *proc1,
					   LOCKMODE lockmode,
					   LOCK *lock,
					   PGPROC *proc2);
extern void InitDeadLockChecking(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);

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

#endif   /* LOCK_H */