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315 lines
10 KiB
C
315 lines
10 KiB
C
/*-------------------------------------------------------------------------
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*
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* lock.h
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* POSTGRES low-level lock mechanism
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*
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*
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* Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/storage/lock.h,v 1.82 2004/08/29 04:13:10 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef LOCK_H_
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#define LOCK_H_
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#include "storage/itemptr.h"
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#include "storage/lwlock.h"
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#include "storage/shmem.h"
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/* originally in procq.h */
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typedef struct PROC_QUEUE
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{
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SHM_QUEUE links; /* head of list of PGPROC objects */
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int size; /* number of entries in list */
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} PROC_QUEUE;
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/* struct PGPROC is declared in proc.h, but must forward-reference it */
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typedef struct PGPROC PGPROC;
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/* GUC variables */
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extern int max_locks_per_xact;
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#ifdef LOCK_DEBUG
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extern int Trace_lock_oidmin;
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extern bool Trace_locks;
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extern bool Trace_userlocks;
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extern int Trace_lock_table;
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extern bool Debug_deadlocks;
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#endif /* LOCK_DEBUG */
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/*
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* LOCKMODE is an integer (1..N) indicating a lock type. LOCKMASK is a bit
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* mask indicating a set of held or requested lock types (the bit 1<<mode
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* corresponds to a particular lock mode).
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*/
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typedef int LOCKMASK;
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typedef int LOCKMODE;
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/* MAX_LOCKMODES cannot be larger than the # of bits in LOCKMASK */
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#define MAX_LOCKMODES 10
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#define LOCKBIT_ON(lockmode) (1 << (lockmode))
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#define LOCKBIT_OFF(lockmode) (~(1 << (lockmode)))
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/*
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* There is normally only one lock method, the default one.
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* If user locks are enabled, an additional lock method is present.
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* Lock methods are identified by LOCKMETHODID.
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*/
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typedef uint16 LOCKMETHODID;
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/* MAX_LOCK_METHODS is the number of distinct lock control tables allowed */
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#define MAX_LOCK_METHODS 3
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#define INVALID_LOCKMETHOD 0
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#define DEFAULT_LOCKMETHOD 1
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#define USER_LOCKMETHOD 2
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#define LockMethodIsValid(lockmethodid) ((lockmethodid) != INVALID_LOCKMETHOD)
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extern int NumLockMethods;
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/*
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* This is the control structure for a lock table. It lives in shared
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* memory. Currently, none of these fields change after startup. In addition
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* to the LockMethodData, a lock table has a shared "lockHash" table holding
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* per-locked-object lock information, and a shared "proclockHash" table
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* holding per-lock-holder/waiter lock information.
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*
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* masterLock -- LWLock used to synchronize access to the table
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*
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* numLockModes -- number of lock types (READ,WRITE,etc) that
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* are defined on this lock table
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*
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* conflictTab -- this is an array of bitmasks showing lock
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* type conflicts. conflictTab[i] is a mask with the j-th bit
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* turned on if lock types i and j conflict.
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*/
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typedef struct LockMethodData
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{
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LWLockId masterLock;
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int numLockModes;
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LOCKMASK conflictTab[MAX_LOCKMODES];
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} LockMethodData;
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typedef LockMethodData *LockMethod;
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/*
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* LOCKTAG is the key information needed to look up a LOCK item in the
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* lock hashtable. A LOCKTAG value uniquely identifies a lockable object.
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*/
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typedef struct LOCKTAG
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{
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Oid relId;
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Oid dbId;
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union
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{
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BlockNumber blkno;
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TransactionId xid;
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} objId;
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/*
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* offnum should be part of objId union above, but doing that would
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* increase sizeof(LOCKTAG) due to padding. Currently used by userlocks
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* only.
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*/
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OffsetNumber offnum;
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LOCKMETHODID lockmethodid; /* needed by userlocks */
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} LOCKTAG;
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/*
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* Per-locked-object lock information:
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*
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* tag -- uniquely identifies the object being locked
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* grantMask -- bitmask for all lock types currently granted on this object.
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* waitMask -- bitmask for all lock types currently awaited on this object.
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* procLocks -- list of PROCLOCK objects for this lock.
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* waitProcs -- queue of processes waiting for this lock.
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* requested -- count of each lock type currently requested on the lock
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* (includes requests already granted!!).
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* nRequested -- total requested locks of all types.
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* granted -- count of each lock type currently granted on the lock.
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* nGranted -- total granted locks of all types.
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*/
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typedef struct LOCK
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{
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/* hash key */
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LOCKTAG tag; /* unique identifier of lockable object */
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/* data */
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LOCKMASK grantMask; /* bitmask for lock types already granted */
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LOCKMASK waitMask; /* bitmask for lock types awaited */
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SHM_QUEUE procLocks; /* list of PROCLOCK objects assoc. with
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* lock */
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PROC_QUEUE waitProcs; /* list of PGPROC objects waiting on lock */
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int requested[MAX_LOCKMODES]; /* counts of requested
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* locks */
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int nRequested; /* total of requested[] array */
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int granted[MAX_LOCKMODES]; /* counts of granted locks */
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int nGranted; /* total of granted[] array */
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} LOCK;
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#define LOCK_LOCKMETHOD(lock) ((lock).tag.lockmethodid)
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/*
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* We may have several different transactions holding or awaiting locks
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* on the same lockable object. We need to store some per-holder/waiter
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* information for each such holder (or would-be holder). This is kept in
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* a PROCLOCK struct.
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*
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* PROCLOCKTAG is the key information needed to look up a PROCLOCK item in the
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* proclock hashtable. A PROCLOCKTAG value uniquely identifies the combination
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* of a lockable object and a holder/waiter for that object.
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*
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* There are two possible kinds of proclock owners: a transaction (identified
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* both by the PGPROC of the backend running it, and the xact's own ID) and
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* a session (identified by backend PGPROC, with XID = InvalidTransactionId).
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*
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* Currently, session proclocks are used for user locks and for cross-xact
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* locks obtained for VACUUM. Note that a single backend can hold locks
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* under several different XIDs at once (including session locks). We treat
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* such locks as never conflicting (a backend can never block itself).
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*
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* The holdMask field shows the already-granted locks represented by this
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* proclock. Note that there will be a proclock object, possibly with
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* zero holdMask, for any lock that the process is currently waiting on.
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* Otherwise, proclock objects whose holdMasks are zero are recycled
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* as soon as convenient.
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*
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* Each PROCLOCK object is linked into lists for both the associated LOCK
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* object and the owning PGPROC object. Note that the PROCLOCK is entered
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* into these lists as soon as it is created, even if no lock has yet been
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* granted. A PGPROC that is waiting for a lock to be granted will also be
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* linked into the lock's waitProcs queue.
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*/
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typedef struct PROCLOCKTAG
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{
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SHMEM_OFFSET lock; /* link to per-lockable-object information */
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SHMEM_OFFSET proc; /* link to PGPROC of owning backend */
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TransactionId xid; /* xact ID, or InvalidTransactionId */
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} PROCLOCKTAG;
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typedef struct PROCLOCK
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{
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/* tag */
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PROCLOCKTAG tag; /* unique identifier of proclock object */
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/* data */
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LOCKMASK holdMask; /* bitmask for lock types currently held */
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SHM_QUEUE lockLink; /* list link for lock's list of proclocks */
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SHM_QUEUE procLink; /* list link for process's list of
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* proclocks */
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} PROCLOCK;
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#define PROCLOCK_LOCKMETHOD(proclock) \
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(((LOCK *) MAKE_PTR((proclock).tag.lock))->tag.lockmethodid)
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/*
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* Each backend also maintains a local hash table with information about each
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* lock it is currently interested in. In particular the local table counts
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* the number of times that lock has been acquired. This allows multiple
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* requests for the same lock to be executed without additional accesses to
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* shared memory. We also track the number of lock acquisitions per
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* ResourceOwner, so that we can release just those locks belonging to a
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* particular ResourceOwner.
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*/
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typedef struct LOCALLOCKTAG
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{
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LOCKTAG lock; /* identifies the lockable object */
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TransactionId xid; /* xact ID, or InvalidTransactionId */
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LOCKMODE mode; /* lock mode for this table entry */
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} LOCALLOCKTAG;
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typedef struct LOCALLOCKOWNER
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{
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/*
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* Note: owner can be NULL to indicate a non-transactional lock.
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* Must use a forward struct reference to avoid circularity.
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*/
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struct ResourceOwnerData *owner;
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int nLocks; /* # of times held by this owner */
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} LOCALLOCKOWNER;
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typedef struct LOCALLOCK
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{
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/* tag */
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LOCALLOCKTAG tag; /* unique identifier of locallock entry */
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/* data */
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LOCK *lock; /* associated LOCK object in shared mem */
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PROCLOCK *proclock; /* associated PROCLOCK object in shmem */
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int nLocks; /* total number of times lock is held */
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int numLockOwners; /* # of relevant ResourceOwners */
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int maxLockOwners; /* allocated size of array */
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LOCALLOCKOWNER *lockOwners; /* dynamically resizable array */
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} LOCALLOCK;
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#define LOCALLOCK_LOCKMETHOD(llock) ((llock).tag.lock.lockmethodid)
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/*
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* This struct holds information passed from lmgr internals to the lock
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* listing user-level functions (lockfuncs.c). For each PROCLOCK in the
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* system, the SHMEM_OFFSET, PROCLOCK itself, and associated PGPROC and
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* LOCK objects are stored. (Note there will often be multiple copies
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* of the same PGPROC or LOCK.) We do not store the SHMEM_OFFSET of the
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* PGPROC or LOCK separately, since they're in the PROCLOCK's tag fields.
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*/
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typedef struct
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{
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int nelements; /* The length of each of the arrays */
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SHMEM_OFFSET *proclockaddrs;
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PROCLOCK *proclocks;
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PGPROC *procs;
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LOCK *locks;
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} LockData;
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/*
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* function prototypes
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*/
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extern void InitLocks(void);
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extern LockMethod GetLocksMethodTable(LOCK *lock);
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extern LOCKMETHODID LockMethodTableInit(const char *tabName,
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const LOCKMASK *conflictsP,
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int numModes, int maxBackends);
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extern LOCKMETHODID LockMethodTableRename(LOCKMETHODID lockmethodid);
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extern bool LockAcquire(LOCKMETHODID lockmethodid, LOCKTAG *locktag,
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TransactionId xid, LOCKMODE lockmode, bool dontWait);
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extern bool LockRelease(LOCKMETHODID lockmethodid, LOCKTAG *locktag,
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TransactionId xid, LOCKMODE lockmode);
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extern bool LockReleaseAll(LOCKMETHODID lockmethodid, bool allxids);
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extern void LockReleaseCurrentOwner(void);
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extern void LockReassignCurrentOwner(void);
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extern int LockCheckConflicts(LockMethod lockMethodTable,
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LOCKMODE lockmode,
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LOCK *lock, PROCLOCK *proclock, PGPROC *proc,
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int *myHolding);
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extern void GrantLock(LOCK *lock, PROCLOCK *proclock, LOCKMODE lockmode);
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extern void GrantAwaitedLock(void);
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extern void RemoveFromWaitQueue(PGPROC *proc);
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extern int LockShmemSize(int maxBackends);
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extern bool DeadLockCheck(PGPROC *proc);
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extern void DeadLockReport(void);
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extern void RememberSimpleDeadLock(PGPROC *proc1,
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LOCKMODE lockmode,
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LOCK *lock,
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PGPROC *proc2);
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extern void InitDeadLockChecking(void);
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extern LockData *GetLockStatusData(void);
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extern const char *GetLockmodeName(LOCKMODE mode);
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#ifdef LOCK_DEBUG
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extern void DumpLocks(void);
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extern void DumpAllLocks(void);
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#endif
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#endif /* LOCK_H */
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