text: /*-------------------------------------------------------------------------
   *
   * proc.h
   *	  per-process shared memory data structures
   *
   *
   * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * src/include/storage/proc.h
   *
   *-------------------------------------------------------------------------
   */
  #ifndef _PROC_H_
  #define _PROC_H_
  
  #include "access/clog.h"
  #include "access/xlogdefs.h"
  #include "lib/ilist.h"
  #include "storage/latch.h"
  #include "storage/lock.h"
  #include "storage/pg_sema.h"
  #include "storage/proclist_types.h"
  
  /*
   * Each backend advertises up to PGPROC_MAX_CACHED_SUBXIDS TransactionIds
   * for non-aborted subtransactions of its current top transaction.  These
   * have to be treated as running XIDs by other backends.
   *
   * We also keep track of whether the cache overflowed (ie, the transaction has
   * generated at least one subtransaction that didn't fit in the cache).
   * If none of the caches have overflowed, we can assume that an XID that's not
   * listed anywhere in the PGPROC array is not a running transaction.  Else we
   * have to look at pg_subtrans.
   */
  #define PGPROC_MAX_CACHED_SUBXIDS 64	/* XXX guessed-at value */
  
  typedef struct XidCacheStatus
  {
  	/* number of cached subxids, never more than PGPROC_MAX_CACHED_SUBXIDS */
  	uint8		count;
  	/* has PGPROC->subxids overflowed */
  	bool		overflowed;
  } XidCacheStatus;
  
  struct XidCache
  {
  	TransactionId xids[PGPROC_MAX_CACHED_SUBXIDS];
  };
  
  /*
   * Flags for PGPROC->statusFlags and PROC_HDR->statusFlags[]
   */
  #define		PROC_IS_AUTOVACUUM	0x01	/* is it an autovac worker? */
  #define		PROC_IN_VACUUM		0x02	/* currently running lazy vacuum */
  #define		PROC_IN_SAFE_IC		0x04	/* currently running CREATE INDEX
  										 * CONCURRENTLY or REINDEX
  										 * CONCURRENTLY on non-expressional,
  										 * non-partial index */
  #define		PROC_VACUUM_FOR_WRAPAROUND	0x08	/* set by autovac only */
  #define		PROC_IN_LOGICAL_DECODING	0x10	/* currently doing logical
  												 * decoding outside xact */
  
  /* flags reset at EOXact */
  #define		PROC_VACUUM_STATE_MASK \
  	(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
  
  /*
   * Flags that are valid to copy from another proc, the parallel leader
   * process in practice.  Currently, flags that are set during parallel
   * vacuum and parallel index creation are allowed.
   */
  #define		PROC_COPYABLE_FLAGS (PROC_IN_VACUUM | PROC_IN_SAFE_IC)
  
  /*
   * We allow a small number of "weak" relation locks (AccessShareLock,
   * RowShareLock, RowExclusiveLock) to be recorded in the PGPROC structure
   * rather than the main lock table.  This eases contention on the lock
   * manager LWLocks.  See storage/lmgr/README for additional details.
   */
  #define		FP_LOCK_SLOTS_PER_BACKEND 16
  
  /*
   * An invalid pgprocno.  Must be larger than the maximum number of PGPROC
   * structures we could possibly have.  See comments for MAX_BACKENDS.
   */
  #define INVALID_PGPROCNO		PG_INT32_MAX
  
  typedef enum
  {
  	PROC_WAIT_STATUS_OK,
  	PROC_WAIT_STATUS_WAITING,
  	PROC_WAIT_STATUS_ERROR,
  } ProcWaitStatus;
  
  /*
   * Each backend has a PGPROC struct in shared memory.  There is also a list of
   * currently-unused PGPROC structs that will be reallocated to new backends.
   *
   * links: list link for any list the PGPROC is in.  When waiting for a lock,
   * the PGPROC is linked into that lock's waitProcs queue.  A recycled PGPROC
   * is linked into ProcGlobal's freeProcs list.
   *
   * Note: twophase.c also sets up a dummy PGPROC struct for each currently
   * prepared transaction.  These PGPROCs appear in the ProcArray data structure
   * so that the prepared transactions appear to be still running and are
   * correctly shown as holding locks.  A prepared transaction PGPROC can be
   * distinguished from a real one at need by the fact that it has pid == 0.
   * The semaphore and lock-activity fields in a prepared-xact PGPROC are unused,
   * but its myProcLocks[] lists are valid.
   *
   * We allow many fields of this struct to be accessed without locks, such as
   * delayChkpt and isBackgroundWorker. However, keep in mind that writing
   * mirrored ones (see below) requires holding ProcArrayLock or XidGenLock in
   * at least shared mode, so that pgxactoff does not change concurrently.
   *
   * Mirrored fields:
   *
   * Some fields in PGPROC (see "mirrored in ..." comment) are mirrored into an
   * element of more densely packed ProcGlobal arrays. These arrays are indexed
   * by PGPROC->pgxactoff. Both copies need to be maintained coherently.
   *
   * NB: The pgxactoff indexed value can *never* be accessed without holding
   * locks.
   *
   * See PROC_HDR for details.
   */
  struct PGPROC
  {
  	/* proc->links MUST BE FIRST IN STRUCT (see ProcSleep,ProcWakeup,etc) */
  	SHM_QUEUE	links;			/* list link if process is in a list */
  	PGPROC	  **procgloballist; /* procglobal list that owns this PGPROC */
  
  	PGSemaphore sem;			/* ONE semaphore to sleep on */
  	ProcWaitStatus waitStatus;
  
  	Latch		procLatch;		/* generic latch for process */
  
  
  	TransactionId xid;			/* id of top-level transaction currently being
  								 * executed by this proc, if running and XID
  								 * is assigned; else InvalidTransactionId.
  								 * mirrored in ProcGlobal->xids[pgxactoff] */
  
  	TransactionId xmin;			/* minimal running XID as it was when we were
  								 * starting our xact, excluding LAZY VACUUM:
  								 * vacuum must not remove tuples deleted by
  								 * xid >= xmin ! */
  
  	LocalTransactionId lxid;	/* local id of top-level transaction currently
  								 * being executed by this proc, if running;
  								 * else InvalidLocalTransactionId */
  	int			pid;			/* Backend's process ID; 0 if prepared xact */
  
  	int			pgxactoff;		/* offset into various ProcGlobal->arrays with
  								 * data mirrored from this PGPROC */
  	int			pgprocno;
  
  	/* These fields are zero while a backend is still starting up: */
  	BackendId	backendId;		/* This backend's backend ID (if assigned) */
  	Oid			databaseId;		/* OID of database this backend is using */
  	Oid			roleId;			/* OID of role using this backend */
  
  	Oid			tempNamespaceId;	/* OID of temp schema this backend is
  									 * using */
  
  	bool		isBackgroundWorker; /* true if background worker. */
  
  	/*
  	 * While in hot standby mode, shows that a conflict signal has been sent
  	 * for the current transaction. Set/cleared while holding ProcArrayLock,
  	 * though not required. Accessed without lock, if needed.
  	 */
  	bool		recoveryConflictPending;
  
  	/* Info about LWLock the process is currently waiting for, if any. */
  	bool		lwWaiting;		/* true if waiting for an LW lock */
  	uint8		lwWaitMode;		/* lwlock mode being waited for */
  	proclist_node lwWaitLink;	/* position in LW lock wait list */
  
  	/* Support for condition variables. */
  	proclist_node cvWaitLink;	/* position in CV wait list */
  
  	/* Info about lock the process is currently waiting for, if any. */
  	/* waitLock and waitProcLock are NULL if not currently waiting. */
  	LOCK	   *waitLock;		/* Lock object we're sleeping on ... */
  	PROCLOCK   *waitProcLock;	/* Per-holder info for awaited lock */
  	LOCKMODE	waitLockMode;	/* type of lock we're waiting for */
  	LOCKMASK	heldLocks;		/* bitmask for lock types already held on this
  								 * lock object by this backend */
  	pg_atomic_uint64 waitStart; /* time at which wait for lock acquisition
  								 * started */
  
  	bool		delayChkpt;		/* true if this proc delays checkpoint start */
  
  	uint8		statusFlags;	/* this backend's status flags, see PROC_*
  								 * above. mirrored in
  								 * ProcGlobal->statusFlags[pgxactoff] */
  
  	/*
  	 * Info to allow us to wait for synchronous replication, if needed.
  	 * waitLSN is InvalidXLogRecPtr if not waiting; set only by user backend.
  	 * syncRepState must not be touched except by owning process or WALSender.
  	 * syncRepLinks used only while holding SyncRepLock.
  	 */
  	XLogRecPtr	waitLSN;		/* waiting for this LSN or higher */
  	int			syncRepState;	/* wait state for sync rep */
  	SHM_QUEUE	syncRepLinks;	/* list link if process is in syncrep queue */
  
  	/*
  	 * All PROCLOCK objects for locks held or awaited by this backend are
  	 * linked into one of these lists, according to the partition number of
  	 * their lock.
  	 */
  	SHM_QUEUE	myProcLocks[NUM_LOCK_PARTITIONS];
  
  	XidCacheStatus subxidStatus;	/* mirrored with
  									 * ProcGlobal->subxidStates[i] */
  	struct XidCache subxids;	/* cache for subtransaction XIDs */
  
  	/* Support for group XID clearing. */
  	/* true, if member of ProcArray group waiting for XID clear */
  	bool		procArrayGroupMember;
  	/* next ProcArray group member waiting for XID clear */
  	pg_atomic_uint32 procArrayGroupNext;
  
  	/*
  	 * latest transaction id among the transaction's main XID and
  	 * subtransactions
  	 */
  	TransactionId procArrayGroupMemberXid;
  
  	uint32		wait_event_info;	/* proc's wait information */
  
  	/* Support for group transaction status update. */
  	bool		clogGroupMember;	/* true, if member of clog group */
  	pg_atomic_uint32 clogGroupNext; /* next clog group member */
  	TransactionId clogGroupMemberXid;	/* transaction id of clog group member */
  	XidStatus	clogGroupMemberXidStatus;	/* transaction status of clog
  											 * group member */
  	int			clogGroupMemberPage;	/* clog page corresponding to
  										 * transaction id of clog group member */
  	XLogRecPtr	clogGroupMemberLsn; /* WAL location of commit record for clog
  									 * group member */
  
  	/* Lock manager data, recording fast-path locks taken by this backend. */
  	LWLock		fpInfoLock;		/* protects per-backend fast-path state */
  	uint64		fpLockBits;		/* lock modes held for each fast-path slot */
  	Oid			fpRelId[FP_LOCK_SLOTS_PER_BACKEND]; /* slots for rel oids */
  	bool		fpVXIDLock;		/* are we holding a fast-path VXID lock? */
  	LocalTransactionId fpLocalTransactionId;	/* lxid for fast-path VXID
  												 * lock */
  
  	/*
  	 * Support for lock groups.  Use LockHashPartitionLockByProc on the group
  	 * leader to get the LWLock protecting these fields.
  	 */
  	PGPROC	   *lockGroupLeader;	/* lock group leader, if I'm a member */
  	dlist_head	lockGroupMembers;	/* list of members, if I'm a leader */
  	dlist_node	lockGroupLink;	/* my member link, if I'm a member */
  };
  
  /* NOTE: "typedef struct PGPROC PGPROC" appears in storage/lock.h. */
  
  
  extern PGDLLIMPORT PGPROC *MyProc;
  
  /*
   * There is one ProcGlobal struct for the whole database cluster.
   *
   * Adding/Removing an entry into the procarray requires holding *both*
   * ProcArrayLock and XidGenLock in exclusive mode (in that order). Both are
   * needed because the dense arrays (see below) are accessed from
   * GetNewTransactionId() and GetSnapshotData(), and we don't want to add
   * further contention by both using the same lock. Adding/Removing a procarray
   * entry is much less frequent.
   *
   * Some fields in PGPROC are mirrored into more densely packed arrays (e.g.
   * xids), with one entry for each backend. These arrays only contain entries
   * for PGPROCs that have been added to the shared array with ProcArrayAdd()
   * (in contrast to PGPROC array which has unused PGPROCs interspersed).
   *
   * The dense arrays are indexed by PGPROC->pgxactoff. Any concurrent
   * ProcArrayAdd() / ProcArrayRemove() can lead to pgxactoff of a procarray
   * member to change.  Therefore it is only safe to use PGPROC->pgxactoff to
   * access the dense array while holding either ProcArrayLock or XidGenLock.
   *
   * As long as a PGPROC is in the procarray, the mirrored values need to be
   * maintained in both places in a coherent manner.
   *
   * The denser separate arrays are beneficial for three main reasons: First, to
   * allow for as tight loops accessing the data as possible. Second, to prevent
   * updates of frequently changing data (e.g. xmin) from invalidating
   * cachelines also containing less frequently changing data (e.g. xid,
   * statusFlags). Third to condense frequently accessed data into as few
   * cachelines as possible.
   *
   * There are two main reasons to have the data mirrored between these dense
   * arrays and PGPROC. First, as explained above, a PGPROC's array entries can
   * only be accessed with either ProcArrayLock or XidGenLock held, whereas the
   * PGPROC entries do not require that (obviously there may still be locking
   * requirements around the individual field, separate from the concerns
   * here). That is particularly important for a backend to efficiently checks
   * it own values, which it often can safely do without locking.  Second, the
   * PGPROC fields allow to avoid unnecessary accesses and modification to the
   * dense arrays. A backend's own PGPROC is more likely to be in a local cache,
   * whereas the cachelines for the dense array will be modified by other
   * backends (often removing it from the cache for other cores/sockets). At
   * commit/abort time a check of the PGPROC value can avoid accessing/dirtying
   * the corresponding array value.
   *
   * Basically it makes sense to access the PGPROC variable when checking a
   * single backend's data, especially when already looking at the PGPROC for
   * other reasons already.  It makes sense to look at the "dense" arrays if we
   * need to look at many / most entries, because we then benefit from the
   * reduced indirection and better cross-process cache-ability.
   *
   * When entering a PGPROC for 2PC transactions with ProcArrayAdd(), the data
   * in the dense arrays is initialized from the PGPROC while it already holds
   * ProcArrayLock.
   */
  typedef struct PROC_HDR
  {
  	/* Array of PGPROC structures (not including dummies for prepared txns) */
  	PGPROC	   *allProcs;
  
  	/* Array mirroring PGPROC.xid for each PGPROC currently in the procarray */
  	TransactionId *xids;
  
  	/*
  	 * Array mirroring PGPROC.subxidStatus for each PGPROC currently in the
  	 * procarray.
  	 */
  	XidCacheStatus *subxidStates;
  
  	/*
  	 * Array mirroring PGPROC.statusFlags for each PGPROC currently in the
  	 * procarray.
  	 */
  	uint8	   *statusFlags;
  
  	/* Length of allProcs array */
  	uint32		allProcCount;
  	/* Head of list of free PGPROC structures */
  	PGPROC	   *freeProcs;
  	/* Head of list of autovacuum's free PGPROC structures */
  	PGPROC	   *autovacFreeProcs;
  	/* Head of list of bgworker free PGPROC structures */
  	PGPROC	   *bgworkerFreeProcs;
  	/* Head of list of walsender free PGPROC structures */
  	PGPROC	   *walsenderFreeProcs;
  	/* First pgproc waiting for group XID clear */
  	pg_atomic_uint32 procArrayGroupFirst;
  	/* First pgproc waiting for group transaction status update */
  	pg_atomic_uint32 clogGroupFirst;
  	/* WALWriter process's latch */
  	Latch	   *walwriterLatch;
  	/* Checkpointer process's latch */
  	Latch	   *checkpointerLatch;
  	/* Current shared estimate of appropriate spins_per_delay value */
  	int			spins_per_delay;
  	/* Buffer id of the buffer that Startup process waits for pin on, or -1 */
  	int			startupBufferPinWaitBufId;
  } PROC_HDR;
  
  extern PGDLLIMPORT PROC_HDR *ProcGlobal;
  
  extern PGPROC *PreparedXactProcs;
  
  /* Accessor for PGPROC given a pgprocno. */
  #define GetPGProcByNumber(n) (&ProcGlobal->allProcs[(n)])
  
  /*
   * We set aside some extra PGPROC structures for auxiliary processes,
   * ie things that aren't full-fledged backends but need shmem access.
   *
   * Background writer, checkpointer, WAL writer and archiver run during normal
   * operation.  Startup process and WAL receiver also consume 2 slots, but WAL
   * writer is launched only after startup has exited, so we only need 5 slots.
   */
  #define NUM_AUXILIARY_PROCS		5
  
  /* configurable options */
  extern PGDLLIMPORT int DeadlockTimeout;
  extern PGDLLIMPORT int StatementTimeout;
  extern PGDLLIMPORT int LockTimeout;
  extern PGDLLIMPORT int IdleInTransactionSessionTimeout;
  extern PGDLLIMPORT int IdleSessionTimeout;
  extern bool log_lock_waits;
  
  
  /*
   * Function Prototypes
   */
  extern int	ProcGlobalSemas(void);
  extern Size ProcGlobalShmemSize(void);
  extern void InitProcGlobal(void);
  extern void InitProcess(void);
  extern void InitProcessPhase2(void);
  extern void InitAuxiliaryProcess(void);
  
  extern void SetStartupBufferPinWaitBufId(int bufid);
  extern int	GetStartupBufferPinWaitBufId(void);
  
  extern bool HaveNFreeProcs(int n);
  extern void ProcReleaseLocks(bool isCommit);
  
  extern void ProcQueueInit(PROC_QUEUE *queue);
  extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable);
  extern PGPROC *ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus);
  extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock);
  extern void CheckDeadLockAlert(void);
  extern bool IsWaitingForLock(void);
  extern void LockErrorCleanup(void);
  
  extern void ProcWaitForSignal(uint32 wait_event_info);
  extern void ProcSendSignal(int pgprocno);
  
  extern PGPROC *AuxiliaryPidGetProc(int pid);
  
  extern void BecomeLockGroupLeader(void);
  extern bool BecomeLockGroupMember(PGPROC *leader, int pid);
  
  #endif							/* _PROC_H_ */
  