* granted -- countof each lock type currently granted on the lock.

* nGranted --total granted locks of all types.

*

* Note: thesecounts count 1 for each backend. Internally to a backend,

* there may bemultiple grabs on a particular lock, but this is not reflected

* into sharedmemory.

*/

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 ofrequested locks */

int nRequested; /* total ofrequested[] array */

int granted[MAX_LOCKMODES];/* counts of granted locks */

int nGranted; /* total ofgranted[] array */

} LOCK;

pg可以有多个不同的backend进程在同一个开锁对象上持有或等待锁。pg需要为每个持有者/等待着存储一些信息。这些保存在结构PROCLOCK里。

PROCLOCKTAG是在proclock哈希表里查找一个PROCLOCK项的关键信息。一个PROCLOCKTAG值唯一的标识一个可锁对象和一个持有者/等待着的组合。（这儿pg能使用指针，因为PROCLOCKTAG仅需要在PROCLOCK的生命周期里唯一，且不会在lock和proc生存期以为）

为了不同的目的，backend进程可以持有同一个锁：独立于会话锁，backend进程跟踪事务锁。但是，这个在共享内存状态中没有反映出来：pg仅跟踪持有锁的backend进程。这是可以的，因为backend进程不能阻塞自己。

holdMask字段显示已经授予的由proclock代表的锁。注意，可能有一个具有0 holdMask的proclock对象，对于任何锁，进程当前正在等待它。负责，holdMask是0的proclock对象在方便的时候被尽快回收。

* releaseMask is workspace for LockReleaseAll(): it showsthe locks due

* to be releasedduring the current call. This must onlybe examined or

* set by thebackend owning the PROCLOCK.

每一个PROCLOCK对象被链接到链表，为了相关LOCK对象和所属PGPROC对象。注意，PROCLOCK对象一被创建就就加入到这些链表，甚至还没有锁lock被授予的时候。等待lock锁被授予的PGPROC进程也会被链接到锁的等待进程（waitProcs）队列。

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; /* uniqueidentifier 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;

每一个backend进程还维持一个本地哈希表，其记录着目前感兴趣的每一个锁lock的信息。特别的，本地表记录着获得的这些锁的时间。这允许不额外访问共享内存的情况下对同一个锁多请求被执行。为了pg能释放属于某个特别资源属主(ResourceOwner)的锁。pg还跟踪每个资源属主(ResourceOwner)获得的锁数

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 heldon behalf of the session;

* otherwise it is held on behalf of my currenttransaction.

*

* Must use a forward struct reference to avoidcircularity.

*/

struct ResourceOwnerData *owner;

int64 nLocks; /* # of times held by this owner */

} LOCALLOCKOWNER;

typedef struct LOCALLOCK

{

/* tag */