lock.h

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/*-------------------------------------------------------------------------
 *
 * lock.h
 *    POSTGRES low-level lock mechanism
 *
 *
 * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/lock.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef LOCK_H_
#define LOCK_H_

#include "storage/backendid.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 VirtualTransactionIdEquals(vxid1, vxid2) \
    ((vxid1).backendId == (vxid2).backendId && \
     (vxid1).localTransactionId == (vxid2).localTransactionId)
#define SetInvalidVirtualTransactionId(vxid) \
    ((vxid).backendId = InvalidBackendId, \
     (vxid).localTransactionId = InvalidLocalTransactionId)
#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).
 * 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.
 *
 * 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.  (The
 * GUC variable is not constant, but we use "const" here to denote that
 * it can't be changed through this reference.)
 */
typedef struct LockMethodData
{
    int         numLockModes;
    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.
 *
 * When holding a lock taken "normally", the lock and proclock fields always
 * point to the associated objects in shared memory.  However, if we acquired
 * the lock via the fast-path mechanism, the lock and proclock fields are set
 * to NULL, since there probably aren't any such objects in shared memory.
 * (If the lock later gets promoted to normal representation, we may eventually
 * update our locallock's lock/proclock fields after finding the shared
 * objects.)
 *
 * Caution: a locallock object can be left over from a failed lock acquisition
 * attempt.  In this case its lock/proclock fields are untrustworthy, since
 * the shared lock object is neither held nor awaited, and hence is available
 * to be reclaimed.  If nLocks > 0 then these pointers must either be valid or
 * NULL, but when nLocks == 0 they should be considered garbage.
 */
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, if any */
    PROCLOCK   *proclock;       /* associated PROCLOCK object, if any */
    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 */
    bool        holdsStrongLockCount;   /* bumped FastPathStrongRelationLocks */
    LOCALLOCKOWNER *lockOwners; /* dynamically resizable array */
} LOCALLOCK;

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


/*
 * These structures hold information passed from lmgr internals to the lock
 * listing user-level functions (in lockfuncs.c).
 */

typedef struct LockInstanceData
{
    LOCKTAG     locktag;        /* locked object */
    LOCKMASK    holdMask;       /* locks held by this PGPROC */
    LOCKMODE    waitLockMode;   /* lock awaited by this PGPROC, if any */
    BackendId   backend;        /* backend ID of this PGPROC */
    LocalTransactionId lxid;    /* local transaction ID of this PGPROC */
    int         pid;            /* pid of this PGPROC */
    bool        fastpath;       /* taken via fastpath? */
} LockInstanceData;

typedef struct LockData
{
    int         nelements;      /* The length of the array */
    LockInstanceData *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) \
    (&MainLWLockArray[LOCK_MANAGER_LWLOCK_OFFSET + \
        LockHashPartition(hashcode)].lock)
#define LockHashPartitionLockByIndex(i) \
    (&MainLWLockArray[LOCK_MANAGER_LWLOCK_OFFSET + (i)].lock)

/*
 * function prototypes
 */
extern void InitLocks(void);
extern LockMethod GetLocksMethodTable(const LOCK *lock);
extern uint32 LockTagHashCode(const LOCKTAG *locktag);
extern bool DoLockModesConflict(LOCKMODE mode1, LOCKMODE mode2);
extern LockAcquireResult LockAcquire(const LOCKTAG *locktag,
            LOCKMODE lockmode,
            bool sessionLock,
            bool dontWait);
extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag,
                    LOCKMODE lockmode,
                    bool sessionLock,
                    bool dontWait,
                    bool report_memory_error);
extern void AbortStrongLockAcquire(void);
extern bool LockRelease(const LOCKTAG *locktag,
            LOCKMODE lockmode, bool sessionLock);
extern void LockReleaseAll(LOCKMETHODID lockmethodid, bool allLocks);
extern void LockReleaseSession(LOCKMETHODID lockmethodid);
extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks);
extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks);
extern bool LockHasWaiters(const LOCKTAG *locktag,
               LOCKMODE lockmode, bool sessionLock);
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);
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 void ReportLockTableError(bool report);

typedef struct xl_standby_lock
{
    TransactionId xid;          /* xid of holder of AccessExclusiveLock */
    Oid         dbOid;
    Oid         relOid;
} xl_standby_lock;

extern xl_standby_lock *GetRunningTransactionLocks(int *nlocks);
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 void lock_twophase_standby_recover(TransactionId xid, uint16 info,
                              void *recdata, uint32 len);

extern DeadLockState DeadLockCheck(PGPROC *proc);
extern PGPROC *GetBlockingAutoVacuumPgproc(void);
extern void DeadLockReport(void) __attribute__((noreturn));
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

/* Lock a VXID (used to wait for a transaction to finish) */
extern void VirtualXactLockTableInsert(VirtualTransactionId vxid);
extern void VirtualXactLockTableCleanup(void);
extern bool VirtualXactLock(VirtualTransactionId vxid, bool wait);

#endif   /* LOCK_H */