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276 lines
8.7 KiB
C
276 lines
8.7 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) 1996-2001, 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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* $Id: lock.h,v 1.51 2001/07/09 22:18:34 tgl 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/ipc.h"
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#include "storage/itemptr.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 PROC objects */
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int size; /* number of entries in list */
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} PROC_QUEUE;
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/* struct proc is declared in storage/proc.h, but must forward-reference it */
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typedef struct proc PROC;
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extern SPINLOCK LockMgrLock;
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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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typedef int LOCKMASK;
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typedef int LOCKMODE;
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typedef int LOCKMETHOD;
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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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/*
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* MAX_LOCK_METHODS corresponds to the number of spin locks allocated in
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* CreateSpinLocks() or the number of shared memory locations allocated
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* for lock table spin locks in the case of machines with TAS instructions.
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*/
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#define MAX_LOCK_METHODS 3
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#define INVALID_TABLEID 0
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#define INVALID_LOCKMETHOD INVALID_TABLEID
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#define DEFAULT_LOCKMETHOD 1
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#define USER_LOCKMETHOD 2
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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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*
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* LOCKMETHODCTL and LOCKMETHODTABLE are split because the first lives
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* in shared memory. This is because it contains a spinlock.
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* LOCKMETHODTABLE exists in private memory. Both are created by the
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* postmaster and should be the same in all backends.
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*/
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/*
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* This is the control structure for a lock table. It
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* lives in shared memory. This information is the same
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* for all backends.
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*
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* lockmethod -- the handle used by the lock table's clients to
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* refer to the type of lock table being used.
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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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* prio -- each lockmode has a priority, so, for example, waiting
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* writers can be given priority over readers (to avoid
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* starvation). XXX this field is not actually used at present!
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*
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* masterlock -- synchronizes access to the table
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*/
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typedef struct LOCKMETHODCTL
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{
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LOCKMETHOD lockmethod;
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int numLockModes;
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int conflictTab[MAX_LOCKMODES];
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int prio[MAX_LOCKMODES];
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SPINLOCK masterLock;
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} LOCKMETHODCTL;
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/*
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* Eack backend has a non-shared lock table header.
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*
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* lockHash -- hash table holding per-locked-object lock information
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* holderHash -- hash table holding per-lock-holder lock information
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* ctl - shared control structure described above.
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*/
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typedef struct LOCKMETHODTABLE
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{
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HTAB *lockHash;
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HTAB *holderHash;
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LOCKMETHODCTL *ctl;
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} LOCKMETHODTABLE;
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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.tupleId above, but would increase
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* sizeof(LOCKTAG) and so moved here; currently used by userlocks
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* only.
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*/
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OffsetNumber offnum;
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uint16 lockmethod; /* 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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* lockHolders -- list of HOLDER 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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int grantMask; /* bitmask for lock types already granted */
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int waitMask; /* bitmask for lock types awaited */
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SHM_QUEUE lockHolders; /* list of HOLDER objects assoc. with lock */
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PROC_QUEUE waitProcs; /* list of PROC 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 SHMEM_LOCKTAB_KEYSIZE sizeof(LOCKTAG)
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#define SHMEM_LOCKTAB_DATASIZE (sizeof(LOCK) - SHMEM_LOCKTAB_KEYSIZE)
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#define LOCK_LOCKMETHOD(lock) ((lock).tag.lockmethod)
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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 information
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* for each such holder (or would-be holder).
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*
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* HOLDERTAG is the key information needed to look up a HOLDER item in the
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* holder hashtable. A HOLDERTAG value uniquely identifies a lock holder.
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*
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* There are two possible kinds of holder tags: a transaction (identified
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* both by the PROC of the backend running it, and the xact's own ID) and
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* a session (identified by backend PROC, with xid = InvalidTransactionId).
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*
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* Currently, session holders are used for user locks and for cross-xact
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* locks obtained for VACUUM. We assume that a session lock never conflicts
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* with per-transaction locks obtained by the same backend.
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*
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* The holding[] array counts the granted locks (of each type) represented
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* by this holder. Note that there will be a holder object, possibly with
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* zero holding[], for any lock that the process is currently waiting on.
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* Otherwise, holder objects whose counts have gone to zero are recycled
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* as soon as convenient.
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*
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* Each HOLDER object is linked into lists for both the associated LOCK object
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* and the owning PROC object. Note that the HOLDER is entered into these
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* lists as soon as it is created, even if no lock has yet been granted.
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* A PROC that is waiting for a lock to be granted will also be linked into
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* the lock's waitProcs queue.
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*/
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typedef struct HOLDERTAG
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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 PROC of owning backend */
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TransactionId xid; /* xact ID, or InvalidTransactionId */
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} HOLDERTAG;
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typedef struct HOLDER
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{
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/* tag */
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HOLDERTAG tag; /* unique identifier of holder object */
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/* data */
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int holding[MAX_LOCKMODES]; /* count of locks currently held */
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int nHolding; /* total of holding[] array */
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SHM_QUEUE lockLink; /* list link for lock's list of holders */
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SHM_QUEUE procLink; /* list link for process's list of holders */
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} HOLDER;
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#define SHMEM_HOLDERTAB_KEYSIZE sizeof(HOLDERTAG)
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#define SHMEM_HOLDERTAB_DATASIZE (sizeof(HOLDER) - SHMEM_HOLDERTAB_KEYSIZE)
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#define HOLDER_LOCKMETHOD(holder) \
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(((LOCK *) MAKE_PTR((holder).tag.lock))->tag.lockmethod)
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#define LockLockTable() SpinAcquire(LockMgrLock)
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#define UnlockLockTable() SpinRelease(LockMgrLock)
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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 void LockDisable(bool status);
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extern bool LockingDisabled(void);
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extern LOCKMETHODTABLE *GetLocksMethodTable(LOCK *lock);
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extern LOCKMETHOD LockMethodTableInit(char *tabName, LOCKMASK *conflictsP,
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int *prioP, int numModes, int maxBackends);
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extern LOCKMETHOD LockMethodTableRename(LOCKMETHOD lockmethod);
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extern bool LockAcquire(LOCKMETHOD lockmethod, LOCKTAG *locktag,
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TransactionId xid, LOCKMODE lockmode, bool dontWait);
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extern bool LockRelease(LOCKMETHOD lockmethod, LOCKTAG *locktag,
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TransactionId xid, LOCKMODE lockmode);
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extern bool LockReleaseAll(LOCKMETHOD lockmethod, PROC *proc,
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bool allxids, TransactionId xid);
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extern int LockCheckConflicts(LOCKMETHODTABLE *lockMethodTable,
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LOCKMODE lockmode,
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LOCK *lock, HOLDER *holder, PROC *proc,
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int *myHolding);
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extern void GrantLock(LOCK *lock, HOLDER *holder, LOCKMODE lockmode);
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extern void RemoveFromWaitQueue(PROC *proc);
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extern int LockShmemSize(int maxBackends);
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extern bool DeadLockCheck(PROC *proc);
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extern void InitDeadLockChecking(void);
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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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