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/*-------------------------------------------------------------------------
*
* lock.h
* POSTGRES low-level lock mechanism
*
*
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/lock.h,v 1.112.2.1 2008/09/16 01:56:35 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#ifndef LOCK_H_
#define LOCK_H_
#include "nodes/pg_list.h"
#include "storage/backendid.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 */
/*
* Top-level transactions are identified by VirtualTransactionIDs comprising
* the BackendId of the backend running the xact, plus a locally-assigned
* LocalTransactionId. These are guaranteed unique over the short term,
* but will be reused after a database restart; hence they should never
* be stored on disk.
*
* Note that struct VirtualTransactionId can not be assumed to be atomically
* assignable as a whole. However, type LocalTransactionId is assumed to
* be atomically assignable, and the backend ID doesn't change often enough
* to be a problem, so we can fetch or assign the two fields separately.
* We deliberately refrain from using the struct within PGPROC, to prevent
* coding errors from trying to use struct assignment with it; instead use
* GET_VXID_FROM_PGPROC().
*/
typedef struct
{
BackendId backendId; /* determined at backend startup */
LocalTransactionId localTransactionId; /* backend-local transaction
* id */
} VirtualTransactionId;
#define InvalidLocalTransactionId 0
#define LocalTransactionIdIsValid(lxid) ((lxid) != InvalidLocalTransactionId)
#define VirtualTransactionIdIsValid(vxid) \
(((vxid).backendId != InvalidBackendId) && \
LocalTransactionIdIsValid((vxid).localTransactionId))
#define GET_VXID_FROM_PGPROC(vxid, proc) \
((vxid).backendId = (proc).backendId, \
(vxid).localTransactionId = (proc).lxid)
/*
* 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),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 */
/*
* 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_VIRTUALTRANSACTION, /* virtual transaction (ditto) */
/* ID info for a virtual transaction is its VirtualTransactionId */
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 old contrib/userlock code */
LOCKTAG_ADVISORY /* advisory user locks */
} LockTagType;
#define LOCKTAG_LAST_TYPE LOCKTAG_ADVISORY
/*
* 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_VIRTUALTRANSACTION(locktag,vxid) \
((locktag).locktag_field1 = (vxid).backendId, \
(locktag).locktag_field2 = (vxid).localTransactionId, \
(locktag).locktag_field3 = 0, \
(locktag).locktag_field4 = 0, \
(locktag).locktag_type = LOCKTAG_VIRTUALTRANSACTION, \
(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)
#define SET_LOCKTAG_ADVISORY(locktag,id1,id2,id3,id4) \
((locktag).locktag_field1 = (id1), \
(locktag).locktag_field2 = (id2), \
(locktag).locktag_field3 = (id3), \
(locktag).locktag_field4 = (id4), \
(locktag).locktag_type = LOCKTAG_ADVISORY, \
(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;
int64 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 */
int64 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;
/* Deadlock states identified by DeadLockCheck() */
typedef enum
{
DS_NOT_YET_CHECKED, /* no deadlock check has run yet */
DS_NO_DEADLOCK, /* no deadlock detected */
DS_SOFT_DEADLOCK, /* deadlock avoided by queue rearrangement */
DS_HARD_DEADLOCK, /* deadlock, no way out but ERROR */
DS_BLOCKED_BY_AUTOVACUUM /* no deadlock; queue blocked by autovacuum
* worker */
} DeadLockState;
/*
* 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 VirtualTransactionId *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 DeadLockState DeadLockCheck(PGPROC *proc);
extern PGPROC *GetBlockingAutoVacuumPgproc(void);
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 */