text: /*-------------------------------------------------------------------------
   *
   * proc.c
   *	  routines to manage per-process shared memory data structure
   *
   * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   *
   * IDENTIFICATION
   *	  src/backend/storage/lmgr/proc.c
   *
   *-------------------------------------------------------------------------
   */
  /*
   * Interface (a):
   *		ProcSleep(), ProcWakeup(),
   *		ProcQueueAlloc() -- create a shm queue for sleeping processes
   *		ProcQueueInit() -- create a queue without allocing memory
   *
   * Waiting for a lock causes the backend to be put to sleep.  Whoever releases
   * the lock wakes the process up again (and gives it an error code so it knows
   * whether it was awoken on an error condition).
   *
   * Interface (b):
   *
   * ProcReleaseLocks -- frees the locks associated with current transaction
   *
   * ProcKill -- destroys the shared memory state (and locks)
   * associated with the process.
   */
  #include "postgres.h"
  
  #include <signal.h>
  #include <unistd.h>
  #include <sys/time.h>
  
  #include "access/transam.h"
  #include "access/twophase.h"
  #include "access/xact.h"
  #include "miscadmin.h"
  #include "pgstat.h"
  #include "postmaster/autovacuum.h"
  #include "replication/slot.h"
  #include "replication/syncrep.h"
  #include "storage/condition_variable.h"
  #include "storage/standby.h"
  #include "storage/ipc.h"
  #include "storage/lmgr.h"
  #include "storage/pmsignal.h"
  #include "storage/proc.h"
  #include "storage/procarray.h"
  #include "storage/procsignal.h"
  #include "storage/spin.h"
  #include "utils/timeout.h"
  #include "utils/timestamp.h"
  
  /* POLAR */
  #include "polar_dma/polar_dma.h"
  
  /* GUC variables */
  int			DeadlockTimeout = 1000;
  int			StatementTimeout = 0;
  int			LockTimeout = 0;
  int			IdleInTransactionSessionTimeout = 0;
  bool		log_lock_waits = false;
  
  /* Pointer to this process's PGPROC and PGXACT structs, if any */
  PGPROC	   *MyProc = NULL;
  PGXACT	   *MyPgXact = NULL;
  
  /*
   * This spinlock protects the freelist of recycled PGPROC structures.
   * We cannot use an LWLock because the LWLock manager depends on already
   * having a PGPROC and a wait semaphore!  But these structures are touched
   * relatively infrequently (only at backend startup or shutdown) and not for
   * very long, so a spinlock is okay.
   */
  NON_EXEC_STATIC slock_t *ProcStructLock = NULL;
  
  /* Pointers to shared-memory structures */
  PROC_HDR   *ProcGlobal = NULL;
  NON_EXEC_STATIC PGPROC *AuxiliaryProcs = NULL;
  PGPROC	   *PreparedXactProcs = NULL;
  
  /* If we are waiting for a lock, this points to the associated LOCALLOCK */
  static LOCALLOCK *lockAwaited = NULL;
  
  static DeadLockState deadlock_state = DS_NOT_YET_CHECKED;
  
  /* Is a deadlock check pending? */
  static volatile sig_atomic_t got_deadlock_timeout;
  
  static void RemoveProcFromArray(int code, Datum arg);
  static void ProcKill(int code, Datum arg);
  static void AuxiliaryProcKill(int code, Datum arg);
  static void CheckDeadLock(void);
  
  
  /*
   * Report shared-memory space needed by InitProcGlobal.
   */
  Size
  ProcGlobalShmemSize(void)
  {
  	Size		size = 0;
  
  	/* ProcGlobal */
  	size = add_size(size, sizeof(PROC_HDR));
  	/* MyProcs, including autovacuum workers and launcher */
  	size = add_size(size, mul_size(MaxBackends, sizeof(PGPROC)));
  	/* AuxiliaryProcs */
  	size = add_size(size, mul_size(NUM_AUXILIARY_PROCS, sizeof(PGPROC)));
  	/* Prepared xacts */
  	size = add_size(size, mul_size(max_prepared_xacts, sizeof(PGPROC)));
  	/* ProcStructLock */
  	size = add_size(size, sizeof(slock_t));
  
  	size = add_size(size, mul_size(MaxBackends, sizeof(PGXACT)));
  	size = add_size(size, mul_size(NUM_AUXILIARY_PROCS, sizeof(PGXACT)));
  	size = add_size(size, mul_size(max_prepared_xacts, sizeof(PGXACT)));
  
  	return size;
  }
  
  /*
   * Report number of semaphores needed by InitProcGlobal.
   */
  int
  ProcGlobalSemas(void)
  {
  	/*
  	 * We need a sema per backend (including autovacuum), plus one for each
  	 * auxiliary process.
  	 */
  	return MaxBackends + NUM_AUXILIARY_PROCS;
  }
  
  /*
   * InitProcGlobal -
   *	  Initialize the global process table during postmaster or standalone
   *	  backend startup.
   *
   *	  We also create all the per-process semaphores we will need to support
   *	  the requested number of backends.  We used to allocate semaphores
   *	  only when backends were actually started up, but that is bad because
   *	  it lets Postgres fail under load --- a lot of Unix systems are
   *	  (mis)configured with small limits on the number of semaphores, and
   *	  running out when trying to start another backend is a common failure.
   *	  So, now we grab enough semaphores to support the desired max number
   *	  of backends immediately at initialization --- if the sysadmin has set
   *	  MaxConnections, max_worker_processes, or autovacuum_max_workers higher
   *	  than his kernel will support, he'll find out sooner rather than later.
   *
   *	  Another reason for creating semaphores here is that the semaphore
   *	  implementation typically requires us to create semaphores in the
   *	  postmaster, not in backends.
   *
   * Note: this is NOT called by individual backends under a postmaster,
   * not even in the EXEC_BACKEND case.  The ProcGlobal and AuxiliaryProcs
   * pointers must be propagated specially for EXEC_BACKEND operation.
   */
  void
  InitProcGlobal(void)
  {
  	PGPROC	   *procs;
  	PGXACT	   *pgxacts;
  	int			i,
  				j;
  	bool		found;
  	uint32		TotalProcs = MaxBackends + NUM_AUXILIARY_PROCS + max_prepared_xacts;
  
  	/* Create the ProcGlobal shared structure */
  	ProcGlobal = (PROC_HDR *)
  		ShmemInitStruct("Proc Header", sizeof(PROC_HDR), &found);
  	Assert(!found);
  
  	/*
  	 * Initialize the data structures.
  	 */
  	ProcGlobal->spins_per_delay = DEFAULT_SPINS_PER_DELAY;
  	ProcGlobal->freeProcs = NULL;
  	ProcGlobal->autovacFreeProcs = NULL;
  	ProcGlobal->bgworkerFreeProcs = NULL;
  	ProcGlobal->startupProc = NULL;
  	ProcGlobal->startupProcPid = 0;
  	ProcGlobal->startupBufferPinWaitBufId = -1;
  	ProcGlobal->walwriterLatch = NULL;
  	ProcGlobal->checkpointerLatch = NULL;
  	pg_atomic_init_u32(&ProcGlobal->procArrayGroupFirst, INVALID_PGPROCNO);
  	pg_atomic_init_u32(&ProcGlobal->clogGroupFirst, INVALID_PGPROCNO);
  
  	/*
  	 * Create and initialize all the PGPROC structures we'll need.  There are
  	 * five separate consumers: (1) normal backends, (2) autovacuum workers
  	 * and the autovacuum launcher, (3) background workers, (4) auxiliary
  	 * processes, and (5) prepared transactions.  Each PGPROC structure is
  	 * dedicated to exactly one of these purposes, and they do not move
  	 * between groups.
  	 */
  	procs = (PGPROC *) ShmemAlloc(TotalProcs * sizeof(PGPROC));
  	MemSet(procs, 0, TotalProcs * sizeof(PGPROC));
  	ProcGlobal->allProcs = procs;
  	/* XXX allProcCount isn't really all of them; it excludes prepared xacts */
  	ProcGlobal->allProcCount = MaxBackends + NUM_AUXILIARY_PROCS;
  
  	/*
  	 * Also allocate a separate array of PGXACT structures.  This is separate
  	 * from the main PGPROC array so that the most heavily accessed data is
  	 * stored contiguously in memory in as few cache lines as possible. This
  	 * provides significant performance benefits, especially on a
  	 * multiprocessor system.  There is one PGXACT structure for every PGPROC
  	 * structure.
  	 */
  	pgxacts = (PGXACT *) ShmemAlloc(TotalProcs * sizeof(PGXACT));
  	MemSet(pgxacts, 0, TotalProcs * sizeof(PGXACT));
  	ProcGlobal->allPgXact = pgxacts;
  
  	for (i = 0; i < TotalProcs; i++)
  	{
  		/* Common initialization for all PGPROCs, regardless of type. */
  
  		/*
  		 * Set up per-PGPROC semaphore, latch, and backendLock. Prepared xact
  		 * dummy PGPROCs don't need these though - they're never associated
  		 * with a real process
  		 */
  		if (i < MaxBackends + NUM_AUXILIARY_PROCS)
  		{
  			procs[i].sem = PGSemaphoreCreate();
  			InitSharedLatch(&(procs[i].procLatch));
  			LWLockInitialize(&(procs[i].backendLock), LWTRANCHE_PROC);
  		}
  		procs[i].pgprocno = i;
  
  		/*
  		 * Newly created PGPROCs for normal backends, autovacuum and bgworkers
  		 * must be queued up on the appropriate free list.  Because there can
  		 * only ever be a small, fixed number of auxiliary processes, no free
  		 * list is used in that case; InitAuxiliaryProcess() instead uses a
  		 * linear search.   PGPROCs for prepared transactions are added to a
  		 * free list by TwoPhaseShmemInit().
  		 */
  		if (i < MaxConnections)
  		{
  			/* PGPROC for normal backend, add to freeProcs list */
  			procs[i].links.next = (SHM_QUEUE *) ProcGlobal->freeProcs;
  			ProcGlobal->freeProcs = &procs[i];
  			procs[i].procgloballist = &ProcGlobal->freeProcs;
  		}
  		else if (i < MaxConnections + autovacuum_max_workers + 1)
  		{
  			/* PGPROC for AV launcher/worker, add to autovacFreeProcs list */
  			procs[i].links.next = (SHM_QUEUE *) ProcGlobal->autovacFreeProcs;
  			ProcGlobal->autovacFreeProcs = &procs[i];
  			procs[i].procgloballist = &ProcGlobal->autovacFreeProcs;
  		}
  		else if (i < MaxBackends)
  		{
  			/* PGPROC for bgworker, add to bgworkerFreeProcs list */
  			procs[i].links.next = (SHM_QUEUE *) ProcGlobal->bgworkerFreeProcs;
  			ProcGlobal->bgworkerFreeProcs = &procs[i];
  			procs[i].procgloballist = &ProcGlobal->bgworkerFreeProcs;
  		}
  
  		/* Initialize myProcLocks[] shared memory queues. */
  		for (j = 0; j < NUM_LOCK_PARTITIONS; j++)
  			SHMQueueInit(&(procs[i].myProcLocks[j]));
  
  		/* Initialize lockGroupMembers list. */
  		dlist_init(&procs[i].lockGroupMembers);
  
  		/*
  		 * Initialize the atomic variables, otherwise, it won't be safe to
  		 * access them for backends that aren't currently in use.
  		 */
  		pg_atomic_init_u32(&(procs[i].procArrayGroupNext), INVALID_PGPROCNO);
  		pg_atomic_init_u32(&(procs[i].clogGroupNext), INVALID_PGPROCNO);
  	}
  
  	/*
  	 * Save pointers to the blocks of PGPROC structures reserved for auxiliary
  	 * processes and prepared transactions.
  	 */
  	AuxiliaryProcs = &procs[MaxBackends];
  	PreparedXactProcs = &procs[MaxBackends + NUM_AUXILIARY_PROCS];
  
  	/* Create ProcStructLock spinlock, too */
  	ProcStructLock = (slock_t *) ShmemAlloc(sizeof(slock_t));
  	SpinLockInit(ProcStructLock);
  }
  
  /*
   * InitProcess -- initialize a per-process data structure for this backend
   */
  void
  InitProcess(void)
  {
  	PGPROC	   *volatile *procgloballist;
  
  	/*
  	 * ProcGlobal should be set up already (if we are a backend, we inherit
  	 * this by fork() or EXEC_BACKEND mechanism from the postmaster).
  	 */
  	if (ProcGlobal == NULL)
  		elog(PANIC, "proc header uninitialized");
  
  	if (MyProc != NULL)
  		elog(ERROR, "you already exist");
  
  	/* Decide which list should supply our PGPROC. */
  	if (IsAnyAutoVacuumProcess())
  		procgloballist = &ProcGlobal->autovacFreeProcs;
  	else if (IsBackgroundWorker)
  		procgloballist = &ProcGlobal->bgworkerFreeProcs;
  	else
  		procgloballist = &ProcGlobal->freeProcs;
  
  	/*
  	 * Try to get a proc struct from the appropriate free list.  If this
  	 * fails, we must be out of PGPROC structures (not to mention semaphores).
  	 *
  	 * While we are holding the ProcStructLock, also copy the current shared
  	 * estimate of spins_per_delay to local storage.
  	 */
  	SpinLockAcquire(ProcStructLock);
  
  	set_spins_per_delay(ProcGlobal->spins_per_delay);
  
  	MyProc = *procgloballist;
  
  	if (MyProc != NULL)
  	{
  		*procgloballist = (PGPROC *) MyProc->links.next;
  		SpinLockRelease(ProcStructLock);
  	}
  	else
  	{
  		/*
  		 * If we reach here, all the PGPROCs are in use.  This is one of the
  		 * possible places to detect "too many backends", so give the standard
  		 * error message.  XXX do we need to give a different failure message
  		 * in the autovacuum case?
  		 */
  		SpinLockRelease(ProcStructLock);
  		ereport(FATAL,
  				(errcode(ERRCODE_TOO_MANY_CONNECTIONS),
  				 errmsg("sorry, too many clients already")));
  	}
  	MyPgXact = &ProcGlobal->allPgXact[MyProc->pgprocno];
  
  	/*
  	 * Cross-check that the PGPROC is of the type we expect; if this were not
  	 * the case, it would get returned to the wrong list.
  	 */
  	Assert(MyProc->procgloballist == procgloballist);
  
  	/*
  	 * Now that we have a PGPROC, mark ourselves as an active postmaster
  	 * child; this is so that the postmaster can detect it if we exit without
  	 * cleaning up.  (XXX autovac launcher currently doesn't participate in
  	 * this; it probably should.)
  	 */
  	if (IsUnderPostmaster && !IsAutoVacuumLauncherProcess())
  		MarkPostmasterChildActive();
  
  	/*
  	 * Initialize all fields of MyProc, except for those previously
  	 * initialized by InitProcGlobal.
  	 */
  	SHMQueueElemInit(&(MyProc->links));
  	MyProc->waitStatus = STATUS_OK;
  	MyProc->lxid = InvalidLocalTransactionId;
  	MyProc->fpVXIDLock = false;
  	MyProc->fpLocalTransactionId = InvalidLocalTransactionId;
  	MyPgXact->xid = InvalidTransactionId;
  	MyPgXact->snapshotcsn = InvalidCommitSeqNo;
  	MyProc->pid = MyProcPid;
  	/* backendId, databaseId and roleId will be filled in later */
  	MyProc->backendId = InvalidBackendId;
  	MyProc->databaseId = InvalidOid;
  	MyProc->roleId = InvalidOid;
  	MyProc->tempNamespaceId = InvalidOid;
  	MyProc->isBackgroundWorker = IsBackgroundWorker;
  	MyPgXact->delayChkpt = false;
  	MyPgXact->vacuumFlags = 0;
  	/* NB -- autovac launcher intentionally does not set IS_AUTOVACUUM */
  	if (IsAutoVacuumWorkerProcess())
  		MyPgXact->vacuumFlags |= PROC_IS_AUTOVACUUM;
  	MyProc->lwWaiting = false;
  	MyProc->lwWaitMode = 0;
  	MyProc->waitLock = NULL;
  	MyProc->waitProcLock = NULL;
  #ifdef USE_ASSERT_CHECKING
  	{
  		int			i;
  
  		/* Last process should have released all locks. */
  		for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
  			Assert(SHMQueueEmpty(&(MyProc->myProcLocks[i])));
  	}
  #endif
  	MyProc->recoveryConflictPending = false;
  
  	/* Initialize fields for sync rep */
  	MyProc->waitLSN = 0;
  	MyProc->syncRepState = SYNC_REP_NOT_WAITING;
  	SHMQueueElemInit(&(MyProc->syncRepLinks));
  
  	/* Initialize fields for consensus rep */
  	if (polar_enable_dma)
  	{
  		ConsensusProcInit(&MyProc->consensusInfo);
  	}
  
  	/* Initialize fields for group XID clearing. */
  	MyProc->procArrayGroupMember = false;
  	MyProc->procArrayGroupMemberXid = InvalidTransactionId;
  	Assert(pg_atomic_read_u32(&MyProc->procArrayGroupNext) == INVALID_PGPROCNO);
  
  	/* Check that group locking fields are in a proper initial state. */
  	Assert(MyProc->lockGroupLeader == NULL);
  	Assert(dlist_is_empty(&MyProc->lockGroupMembers));
  
  	/* Initialize wait event information. */
  	MyProc->wait_event_info = 0;
  
  	/* Initialize fields for group transaction status update. */
  	MyProc->clogGroupMember = false;
  	MyProc->clogGroupMemberXid = InvalidTransactionId;
  	MyProc->clogGroupMemberXidStatus = CLOG_XID_STATUS_IN_PROGRESS;
  	MyProc->clogGroupMemberPage = -1;
  	MyProc->clogGroupMemberLsn = InvalidXLogRecPtr;
  	MyProc->clogGroupNSubxids = 0;
  	pg_atomic_init_u32(&MyProc->clogGroupNext, INVALID_PGPROCNO);
  
  	/*
  	 * Acquire ownership of the PGPROC's latch, so that we can use WaitLatch
  	 * on it.  That allows us to repoint the process latch, which so far
  	 * points to process local one, to the shared one.
  	 */
  	OwnLatch(&MyProc->procLatch);
  	SwitchToSharedLatch();
  
  	/*
  	 * We might be reusing a semaphore that belonged to a failed process. So
  	 * be careful and reinitialize its value here.  (This is not strictly
  	 * necessary anymore, but seems like a good idea for cleanliness.)
  	 */
  	PGSemaphoreReset(MyProc->sem);
  
  	/*
  	 * Arrange to clean up at backend exit.
  	 */
  	on_shmem_exit(ProcKill, 0);
  
  	/*
  	 * Now that we have a PGPROC, we could try to acquire locks, so initialize
  	 * local state needed for LWLocks, and the deadlock checker.
  	 */
  	InitLWLockAccess();
  	InitDeadLockChecking();
  }
  
  /*
   * InitProcessPhase2 -- make MyProc visible in the shared ProcArray.
   *
   * This is separate from InitProcess because we can't acquire LWLocks until
   * we've created a PGPROC, but in the EXEC_BACKEND case ProcArrayAdd won't
   * work until after we've done CreateSharedMemoryAndSemaphores.
   */
  void
  InitProcessPhase2(void)
  {
  	Assert(MyProc != NULL);
  
  	/*
  	 * Add our PGPROC to the PGPROC array in shared memory.
  	 */
  	ProcArrayAdd(MyProc);
  
  	/*
  	 * Arrange to clean that up at backend exit.
  	 */
  	on_shmem_exit(RemoveProcFromArray, 0);
  }
  
  /*
   * InitAuxiliaryProcess -- create a per-auxiliary-process data structure
   *
   * This is called by bgwriter and similar processes so that they will have a
   * MyProc value that's real enough to let them wait for LWLocks.  The PGPROC
   * and sema that are assigned are one of the extra ones created during
   * InitProcGlobal.
   *
   * Auxiliary processes are presently not expected to wait for real (lockmgr)
   * locks, so we need not set up the deadlock checker.  They are never added
   * to the ProcArray or the sinval messaging mechanism, either.  They also
   * don't get a VXID assigned, since this is only useful when we actually
   * hold lockmgr locks.
   *
   * Startup process however uses locks but never waits for them in the
   * normal backend sense. Startup process also takes part in sinval messaging
   * as a sendOnly process, so never reads messages from sinval queue. So
   * Startup process does have a VXID and does show up in pg_locks.
   */
  void
  InitAuxiliaryProcess(void)
  {
  	PGPROC	   *auxproc;
  	int			proctype;
  
  	/*
  	 * ProcGlobal should be set up already (if we are a backend, we inherit
  	 * this by fork() or EXEC_BACKEND mechanism from the postmaster).
  	 */
  	if (ProcGlobal == NULL || AuxiliaryProcs == NULL)
  		elog(PANIC, "proc header uninitialized");
  
  	if (MyProc != NULL)
  		elog(ERROR, "you already exist");
  
  	/*
  	 * We use the ProcStructLock to protect assignment and releasing of
  	 * AuxiliaryProcs entries.
  	 *
  	 * While we are holding the ProcStructLock, also copy the current shared
  	 * estimate of spins_per_delay to local storage.
  	 */
  	SpinLockAcquire(ProcStructLock);
  
  	set_spins_per_delay(ProcGlobal->spins_per_delay);
  
  	/*
  	 * Find a free auxproc ... *big* trouble if there isn't one ...
  	 */
  	for (proctype = 0; proctype < NUM_AUXILIARY_PROCS; proctype++)
  	{
  		auxproc = &AuxiliaryProcs[proctype];
  		if (auxproc->pid == 0)
  			break;
  	}
  	if (proctype >= NUM_AUXILIARY_PROCS)
  	{
  		SpinLockRelease(ProcStructLock);
  		elog(FATAL, "all AuxiliaryProcs are in use");
  	}
  
  	/* Mark auxiliary proc as in use by me */
  	/* use volatile pointer to prevent code rearrangement */
  	((volatile PGPROC *) auxproc)->pid = MyProcPid;
  
  	MyProc = auxproc;
  	MyPgXact = &ProcGlobal->allPgXact[auxproc->pgprocno];
  
  	SpinLockRelease(ProcStructLock);
  
  	/*
  	 * Initialize all fields of MyProc, except for those previously
  	 * initialized by InitProcGlobal.
  	 */
  	SHMQueueElemInit(&(MyProc->links));
  	MyProc->waitStatus = STATUS_OK;
  	MyProc->lxid = InvalidLocalTransactionId;
  	MyProc->fpVXIDLock = false;
  	MyProc->fpLocalTransactionId = InvalidLocalTransactionId;
  	MyPgXact->xid = InvalidTransactionId;
  	MyPgXact->snapshotcsn = InvalidCommitSeqNo;
  	MyProc->backendId = InvalidBackendId;
  	MyProc->databaseId = InvalidOid;
  	MyProc->roleId = InvalidOid;
  	MyProc->tempNamespaceId = InvalidOid;
  	MyProc->isBackgroundWorker = IsBackgroundWorker;
  	MyPgXact->delayChkpt = false;
  	MyPgXact->vacuumFlags = 0;
  	MyProc->lwWaiting = false;
  	MyProc->lwWaitMode = 0;
  	MyProc->waitLock = NULL;
  	MyProc->waitProcLock = NULL;
  #ifdef USE_ASSERT_CHECKING
  	{
  		int			i;
  
  		/* Last process should have released all locks. */
  		for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
  			Assert(SHMQueueEmpty(&(MyProc->myProcLocks[i])));
  	}
  #endif
  
  	/* Initialize fields for consensus rep */
  	if (polar_enable_dma)
  	{
  		ConsensusProcInit(&MyProc->consensusInfo);
  	}
  
  	/*
  	 * Acquire ownership of the PGPROC's latch, so that we can use WaitLatch
  	 * on it.  That allows us to repoint the process latch, which so far
  	 * points to process local one, to the shared one.
  	 */
  	OwnLatch(&MyProc->procLatch);
  	SwitchToSharedLatch();
  
  	/* Check that group locking fields are in a proper initial state. */
  	Assert(MyProc->lockGroupLeader == NULL);
  	Assert(dlist_is_empty(&MyProc->lockGroupMembers));
  
  	/*
  	 * We might be reusing a semaphore that belonged to a failed process. So
  	 * be careful and reinitialize its value here.  (This is not strictly
  	 * necessary anymore, but seems like a good idea for cleanliness.)
  	 */
  	PGSemaphoreReset(MyProc->sem);
  
  	/*
  	 * Arrange to clean up at process exit.
  	 */
  	on_shmem_exit(AuxiliaryProcKill, Int32GetDatum(proctype));
  }
  
  /*
   * Record the PID and PGPROC structures for the Startup process, for use in
   * ProcSendSignal().  See comments there for further explanation.
   */
  void
  PublishStartupProcessInformation(void)
  {
  	SpinLockAcquire(ProcStructLock);
  
  	ProcGlobal->startupProc = MyProc;
  	ProcGlobal->startupProcPid = MyProcPid;
  
  	SpinLockRelease(ProcStructLock);
  }
  
  /*
   * Used from bufgr to share the value of the buffer that Startup waits on,
   * or to reset the value to "not waiting" (-1). This allows processing
   * of recovery conflicts for buffer pins. Set is made before backends look
   * at this value, so locking not required, especially since the set is
   * an atomic integer set operation.
   */
  void
  SetStartupBufferPinWaitBufId(int bufid)
  {
  	/* use volatile pointer to prevent code rearrangement */
  	volatile PROC_HDR *procglobal = ProcGlobal;
  
  	procglobal->startupBufferPinWaitBufId = bufid;
  }
  
  /*
   * Used by backends when they receive a request to check for buffer pin waits.
   */
  int
  GetStartupBufferPinWaitBufId(void)
  {
  	/* use volatile pointer to prevent code rearrangement */
  	volatile PROC_HDR *procglobal = ProcGlobal;
  
  	return procglobal->startupBufferPinWaitBufId;
  }
  
  /*
   * Check whether there are at least N free PGPROC objects.
   *
   * Note: this is designed on the assumption that N will generally be small.
   */
  bool
  HaveNFreeProcs(int n)
  {
  	PGPROC	   *proc;
  
  	SpinLockAcquire(ProcStructLock);
  
  	proc = ProcGlobal->freeProcs;
  
  	while (n > 0 && proc != NULL)
  	{
  		proc = (PGPROC *) proc->links.next;
  		n--;
  	}
  
  	SpinLockRelease(ProcStructLock);
  
  	return (n <= 0);
  }
  
  /*
   * Check if the current process is awaiting a lock.
   */
  bool
  IsWaitingForLock(void)
  {
  	if (lockAwaited == NULL)
  		return false;
  
  	return true;
  }
  
  /*
   * Cancel any pending wait for lock, when aborting a transaction, and revert
   * any strong lock count acquisition for a lock being acquired.
   *
   * (Normally, this would only happen if we accept a cancel/die
   * interrupt while waiting; but an ereport(ERROR) before or during the lock
   * wait is within the realm of possibility, too.)
   */
  void
  LockErrorCleanup(void)
  {
  	LWLock	   *partitionLock;
  	DisableTimeoutParams timeouts[2];
  
  	HOLD_INTERRUPTS();
  
  	AbortStrongLockAcquire();
  
  	/* Nothing to do if we weren't waiting for a lock */
  	if (lockAwaited == NULL)
  	{
  		RESUME_INTERRUPTS();
  		return;
  	}
  
  	/*
  	 * Turn off the deadlock and lock timeout timers, if they are still
  	 * running (see ProcSleep).  Note we must preserve the LOCK_TIMEOUT
  	 * indicator flag, since this function is executed before
  	 * ProcessInterrupts when responding to SIGINT; else we'd lose the
  	 * knowledge that the SIGINT came from a lock timeout and not an external
  	 * source.
  	 */
  	timeouts[0].id = DEADLOCK_TIMEOUT;
  	timeouts[0].keep_indicator = false;
  	timeouts[1].id = LOCK_TIMEOUT;
  	timeouts[1].keep_indicator = true;
  	disable_timeouts(timeouts, 2);
  
  	/* Unlink myself from the wait queue, if on it (might not be anymore!) */
  	partitionLock = LockHashPartitionLock(lockAwaited->hashcode);
  	LWLockAcquire(partitionLock, LW_EXCLUSIVE);
  
  	if (MyProc->links.next != NULL)
  	{
  		/* We could not have been granted the lock yet */
  		RemoveFromWaitQueue(MyProc, lockAwaited->hashcode);
  	}
  	else
  	{
  		/*
  		 * Somebody kicked us off the lock queue already.  Perhaps they
  		 * granted us the lock, or perhaps they detected a deadlock. If they
  		 * did grant us the lock, we'd better remember it in our local lock
  		 * table.
  		 */
  		if (MyProc->waitStatus == STATUS_OK)
  			GrantAwaitedLock();
  	}
  
  	lockAwaited = NULL;
  
  	LWLockRelease(partitionLock);
  
  	RESUME_INTERRUPTS();
  }
  
  
  /*
   * ProcReleaseLocks() -- release locks associated with current transaction
   *			at main transaction commit or abort
   *
   * At main transaction commit, we release standard locks except session locks.
   * At main transaction abort, we release all locks including session locks.
   *
   * Advisory locks are released only if they are transaction-level;
   * session-level holds remain, whether this is a commit or not.
   *
   * At subtransaction commit, we don't release any locks (so this func is not
   * needed at all); we will defer the releasing to the parent transaction.
   * At subtransaction abort, we release all locks held by the subtransaction;
   * this is implemented by retail releasing of the locks under control of
   * the ResourceOwner mechanism.
   */
  void
  ProcReleaseLocks(bool isCommit)
  {
  	if (!MyProc)
  		return;
  	/* If waiting, get off wait queue (should only be needed after error) */
  	LockErrorCleanup();
  	/* Release standard locks, including session-level if aborting */
  	LockReleaseAll(DEFAULT_LOCKMETHOD, !isCommit);
  	/* Release transaction-level advisory locks */
  	LockReleaseAll(USER_LOCKMETHOD, false);
  }
  
  
  /*
   * RemoveProcFromArray() -- Remove this process from the shared ProcArray.
   */
  static void
  RemoveProcFromArray(int code, Datum arg)
  {
  	Assert(MyProc != NULL);
  	ProcArrayRemove(MyProc);
  }
  
  /*
   * ProcKill() -- Destroy the per-proc data structure for
   *		this process. Release any of its held LW locks.
   */
  static void
  ProcKill(int code, Datum arg)
  {
  	PGPROC	   *proc;
  	PGPROC	   *volatile *procgloballist;
  
  	Assert(MyProc != NULL);
  
  	/* Make sure we're out of the sync rep lists */
  	SyncRepCleanupAtProcExit();
  
  #ifdef USE_ASSERT_CHECKING
  	{
  		int			i;
  
  		/* Last process should have released all locks. */
  		for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
  			Assert(SHMQueueEmpty(&(MyProc->myProcLocks[i])));
  	}
  #endif
  
  	/*
  	 * Release any LW locks I am holding.  There really shouldn't be any, but
  	 * it's cheap to check again before we cut the knees off the LWLock
  	 * facility by releasing our PGPROC ...
  	 */
  	LWLockReleaseAll();
  
  	/* Cancel any pending condition variable sleep, too */
  	ConditionVariableCancelSleep();
  
  	/* Make sure active replication slots are released */
  	if (MyReplicationSlot != NULL)
  		ReplicationSlotRelease();
  
  	/* Also cleanup all the temporary slots. */
  	ReplicationSlotCleanup();
  
  	/*
  	 * Detach from any lock group of which we are a member.  If the leader
  	 * exist before all other group members, it's PGPROC will remain allocated
  	 * until the last group process exits; that process must return the
  	 * leader's PGPROC to the appropriate list.
  	 */
  	if (MyProc->lockGroupLeader != NULL)
  	{
  		PGPROC	   *leader = MyProc->lockGroupLeader;
  		LWLock	   *leader_lwlock = LockHashPartitionLockByProc(leader);
  
  		LWLockAcquire(leader_lwlock, LW_EXCLUSIVE);
  		Assert(!dlist_is_empty(&leader->lockGroupMembers));
  		dlist_delete(&MyProc->lockGroupLink);
  		if (dlist_is_empty(&leader->lockGroupMembers))
  		{
  			leader->lockGroupLeader = NULL;
  			if (leader != MyProc)
  			{
  				procgloballist = leader->procgloballist;
  
  				/* Leader exited first; return its PGPROC. */
  				SpinLockAcquire(ProcStructLock);
  				leader->links.next = (SHM_QUEUE *) *procgloballist;
  				*procgloballist = leader;
  				SpinLockRelease(ProcStructLock);
  			}
  		}
  		else if (leader != MyProc)
  			MyProc->lockGroupLeader = NULL;
  		LWLockRelease(leader_lwlock);
  	}
  
  	/*
  	 * Reset MyLatch to the process local one.  This is so that signal
  	 * handlers et al can continue using the latch after the shared latch
  	 * isn't ours anymore. After that clear MyProc and disown the shared
  	 * latch.
  	 */
  	SwitchBackToLocalLatch();
  	proc = MyProc;
  	MyProc = NULL;
  	DisownLatch(&proc->procLatch);
  
  	procgloballist = proc->procgloballist;
  	SpinLockAcquire(ProcStructLock);
  
  	/*
  	 * If we're still a member of a locking group, that means we're a leader
  	 * which has somehow exited before its children.  The last remaining child
  	 * will release our PGPROC.  Otherwise, release it now.
  	 */
  	if (proc->lockGroupLeader == NULL)
  	{
  		/* Since lockGroupLeader is NULL, lockGroupMembers should be empty. */
  		Assert(dlist_is_empty(&proc->lockGroupMembers));
  
  		/* Return PGPROC structure (and semaphore) to appropriate freelist */
  		proc->links.next = (SHM_QUEUE *) *procgloballist;
  		*procgloballist = proc;
  	}
  
  	/* Update shared estimate of spins_per_delay */
  	ProcGlobal->spins_per_delay = update_spins_per_delay(ProcGlobal->spins_per_delay);
  
  	SpinLockRelease(ProcStructLock);
  
  	/*
  	 * This process is no longer present in shared memory in any meaningful
  	 * way, so tell the postmaster we've cleaned up acceptably well. (XXX
  	 * autovac launcher should be included here someday)
  	 */
  	if (IsUnderPostmaster && !IsAutoVacuumLauncherProcess())
  		MarkPostmasterChildInactive();
  
  	/* wake autovac launcher if needed -- see comments in FreeWorkerInfo */
  	if (AutovacuumLauncherPid != 0)
  		kill(AutovacuumLauncherPid, SIGUSR2);
  }
  
  /*
   * AuxiliaryProcKill() -- Cut-down version of ProcKill for auxiliary
   *		processes (bgwriter, etc).  The PGPROC and sema are not released, only
   *		marked as not-in-use.
   */
  static void
  AuxiliaryProcKill(int code, Datum arg)
  {
  	int			proctype = DatumGetInt32(arg);
  	PGPROC	   *auxproc PG_USED_FOR_ASSERTS_ONLY;
  	PGPROC	   *proc;
  
  	Assert(proctype >= 0 && proctype < NUM_AUXILIARY_PROCS);
  
  	auxproc = &AuxiliaryProcs[proctype];
  
  	Assert(MyProc == auxproc);
  
  	/* Release any LW locks I am holding (see notes above) */
  	LWLockReleaseAll();
  
  	/* Cancel any pending condition variable sleep, too */
  	ConditionVariableCancelSleep();
  
  	/*
  	 * Reset MyLatch to the process local one.  This is so that signal
  	 * handlers et al can continue using the latch after the shared latch
  	 * isn't ours anymore. After that clear MyProc and disown the shared
  	 * latch.
  	 */
  	SwitchBackToLocalLatch();
  	proc = MyProc;
  	MyProc = NULL;
  	DisownLatch(&proc->procLatch);
  
  	SpinLockAcquire(ProcStructLock);
  
  	/* Mark auxiliary proc no longer in use */
  	proc->pid = 0;
  
  	/* Update shared estimate of spins_per_delay */
  	ProcGlobal->spins_per_delay = update_spins_per_delay(ProcGlobal->spins_per_delay);
  
  	SpinLockRelease(ProcStructLock);
  }
  
  /*
   * AuxiliaryPidGetProc -- get PGPROC for an auxiliary process
   * given its PID
   *
   * Returns NULL if not found.
   */
  PGPROC *
  AuxiliaryPidGetProc(int pid)
  {
  	PGPROC	   *result = NULL;
  	int			index;
  
  	if (pid == 0)				/* never match dummy PGPROCs */
  		return NULL;
  
  	for (index = 0; index < NUM_AUXILIARY_PROCS; index++)
  	{
  		PGPROC	   *proc = &AuxiliaryProcs[index];
  
  		if (proc->pid == pid)
  		{
  			result = proc;
  			break;
  		}
  	}
  	return result;
  }
  
  /*
   * ProcQueue package: routines for putting processes to sleep
   *		and  waking them up
   */
  
  /*
   * ProcQueueAlloc -- alloc/attach to a shared memory process queue
   *
   * Returns: a pointer to the queue
   * Side Effects: Initializes the queue if it wasn't there before
   */
  #ifdef NOT_USED
  PROC_QUEUE *
  ProcQueueAlloc(const char *name)
  {
  	PROC_QUEUE *queue;
  	bool		found;
  
  	queue = (PROC_QUEUE *)
  		ShmemInitStruct(name, sizeof(PROC_QUEUE), &found);
  
  	if (!found)
  		ProcQueueInit(queue);
  
  	return queue;
  }
  #endif
  
  /*
   * ProcQueueInit -- initialize a shared memory process queue
   */
  void
  ProcQueueInit(PROC_QUEUE *queue)
  {
  	SHMQueueInit(&(queue->links));
  	queue->size = 0;
  }
  
  
  /*
   * ProcSleep -- put a process to sleep on the specified lock
   *
   * Caller must have set MyProc->heldLocks to reflect locks already held
   * on the lockable object by this process (under all XIDs).
   *
   * The lock table's partition lock must be held at entry, and will be held
   * at exit.
   *
   * Result: STATUS_OK if we acquired the lock, STATUS_ERROR if not (deadlock).
   *
   * ASSUME: that no one will fiddle with the queue until after
   *		we release the partition lock.
   *
   * NOTES: The process queue is now a priority queue for locking.
   */
  int
  ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
  {
  	LOCKMODE	lockmode = locallock->tag.mode;
  	LOCK	   *lock = locallock->lock;
  	PROCLOCK   *proclock = locallock->proclock;
  	uint32		hashcode = locallock->hashcode;
  	LWLock	   *partitionLock = LockHashPartitionLock(hashcode);
  	PROC_QUEUE *waitQueue = &(lock->waitProcs);
  	LOCKMASK	myHeldLocks = MyProc->heldLocks;
  	bool		early_deadlock = false;
  	bool		allow_autovacuum_cancel = true;
  	int			myWaitStatus;
  	PGPROC	   *proc;
  	PGPROC	   *leader = MyProc->lockGroupLeader;
  	int			i;
  
  	/*
  	 * If group locking is in use, locks held by members of my locking group
  	 * need to be included in myHeldLocks.
  	 */
  	if (leader != NULL)
  	{
  		SHM_QUEUE  *procLocks = &(lock->procLocks);
  		PROCLOCK   *otherproclock;
  
  		otherproclock = (PROCLOCK *)
  			SHMQueueNext(procLocks, procLocks, offsetof(PROCLOCK, lockLink));
  		while (otherproclock != NULL)
  		{
  			if (otherproclock->groupLeader == leader)
  				myHeldLocks |= otherproclock->holdMask;
  			otherproclock = (PROCLOCK *)
  				SHMQueueNext(procLocks, &otherproclock->lockLink,
  							 offsetof(PROCLOCK, lockLink));
  		}
  	}
  
  	/*
  	 * Determine where to add myself in the wait queue.
  	 *
  	 * Normally I should go at the end of the queue.  However, if I already
  	 * hold locks that conflict with the request of any previous waiter, put
  	 * myself in the queue just in front of the first such waiter. This is not
  	 * a necessary step, since deadlock detection would move me to before that
  	 * waiter anyway; but it's relatively cheap to detect such a conflict
  	 * immediately, and avoid delaying till deadlock timeout.
  	 *
  	 * Special case: if I find I should go in front of some waiter, check to
  	 * see if I conflict with already-held locks or the requests before that
  	 * waiter.  If not, then just grant myself the requested lock immediately.
  	 * This is the same as the test for immediate grant in LockAcquire, except
  	 * we are only considering the part of the wait queue before my insertion
  	 * point.
  	 */
  	if (myHeldLocks != 0)
  	{
  		LOCKMASK	aheadRequests = 0;
  
  		proc = (PGPROC *) waitQueue->links.next;
  		for (i = 0; i < waitQueue->size; i++)
  		{
  			/*
  			 * If we're part of the same locking group as this waiter, its
  			 * locks neither conflict with ours nor contribute to
  			 * aheadRequests.
  			 */
  			if (leader != NULL && leader == proc->lockGroupLeader)
  			{
  				proc = (PGPROC *) proc->links.next;
  				continue;
  			}
  			/* Must he wait for me? */
  			if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks)
  			{
  				/* Must I wait for him ? */
  				if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks)
  				{
  					/*
  					 * Yes, so we have a deadlock.  Easiest way to clean up
  					 * correctly is to call RemoveFromWaitQueue(), but we
  					 * can't do that until we are *on* the wait queue. So, set
  					 * a flag to check below, and break out of loop.  Also,
  					 * record deadlock info for later message.
  					 */
  					RememberSimpleDeadLock(MyProc, lockmode, lock, proc);
  					early_deadlock = true;
  					break;
  				}
  				/* I must go before this waiter.  Check special case. */
  				if ((lockMethodTable->conflictTab[lockmode] & aheadRequests) == 0 &&
  					LockCheckConflicts(lockMethodTable,
  									   lockmode,
  									   lock,
  									   proclock) == STATUS_OK)
  				{
  					/* Skip the wait and just grant myself the lock. */
  					GrantLock(lock, proclock, lockmode);
  					GrantAwaitedLock();
  					return STATUS_OK;
  				}
  				/* Break out of loop to put myself before him */
  				break;
  			}
  			/* Nope, so advance to next waiter */
  			aheadRequests |= LOCKBIT_ON(proc->waitLockMode);
  			proc = (PGPROC *) proc->links.next;
  		}
  
  		/*
  		 * If we fall out of loop normally, proc points to waitQueue head, so
  		 * we will insert at tail of queue as desired.
  		 */
  	}
  	else
  	{
  		/* I hold no locks, so I can't push in front of anyone. */
  		proc = (PGPROC *) &(waitQueue->links);
  	}
  
  	/*
  	 * Insert self into queue, ahead of the given proc (or at tail of queue).
  	 */
  	SHMQueueInsertBefore(&(proc->links), &(MyProc->links));
  	waitQueue->size++;
  
  	lock->waitMask |= LOCKBIT_ON(lockmode);
  
  	/* Set up wait information in PGPROC object, too */
  	MyProc->waitLock = lock;
  	MyProc->waitProcLock = proclock;
  	MyProc->waitLockMode = lockmode;
  
  	MyProc->waitStatus = STATUS_WAITING;
  
  	/*
  	 * If we detected deadlock, give up without waiting.  This must agree with
  	 * CheckDeadLock's recovery code, except that we shouldn't release the
  	 * semaphore since we haven't tried to lock it yet.
  	 */
  	if (early_deadlock)
  	{
  		RemoveFromWaitQueue(MyProc, hashcode);
  		return STATUS_ERROR;
  	}
  
  	/* mark that we are waiting for a lock */
  	lockAwaited = locallock;
  
  	/*
  	 * Release the lock table's partition lock.
  	 *
  	 * NOTE: this may also cause us to exit critical-section state, possibly
  	 * allowing a cancel/die interrupt to be accepted. This is OK because we
  	 * have recorded the fact that we are waiting for a lock, and so
  	 * LockErrorCleanup will clean up if cancel/die happens.
  	 */
  	LWLockRelease(partitionLock);
  
  	/*
  	 * Also, now that we will successfully clean up after an ereport, it's
  	 * safe to check to see if there's a buffer pin deadlock against the
  	 * Startup process.  Of course, that's only necessary if we're doing Hot
  	 * Standby and are not the Startup process ourselves.
  	 */
  	if (RecoveryInProgress() && !InRecovery)
  		CheckRecoveryConflictDeadlock();
  
  	/* Reset deadlock_state before enabling the timeout handler */
  	deadlock_state = DS_NOT_YET_CHECKED;
  	got_deadlock_timeout = false;
  
  	/*
  	 * Set timer so we can wake up after awhile and check for a deadlock. If a
  	 * deadlock is detected, the handler releases the process's semaphore and
  	 * sets MyProc->waitStatus = STATUS_ERROR, allowing us to know that we
  	 * must report failure rather than success.
  	 *
  	 * By delaying the check until we've waited for a bit, we can avoid
  	 * running the rather expensive deadlock-check code in most cases.
  	 *
  	 * If LockTimeout is set, also enable the timeout for that.  We can save a
  	 * few cycles by enabling both timeout sources in one call.
  	 *
  	 * If InHotStandby we set lock waits slightly later for clarity with other
  	 * code.
  	 */
  	if (!InHotStandby)
  	{
  		if (LockTimeout > 0)
  		{
  			EnableTimeoutParams timeouts[2];
  
  			timeouts[0].id = DEADLOCK_TIMEOUT;
  			timeouts[0].type = TMPARAM_AFTER;
  			timeouts[0].delay_ms = DeadlockTimeout;
  			timeouts[1].id = LOCK_TIMEOUT;
  			timeouts[1].type = TMPARAM_AFTER;
  			timeouts[1].delay_ms = LockTimeout;
  			enable_timeouts(timeouts, 2);
  		}
  		else
  			enable_timeout_after(DEADLOCK_TIMEOUT, DeadlockTimeout);
  	}
  
  	/*
  	 * If somebody wakes us between LWLockRelease and WaitLatch, the latch
  	 * will not wait. But a set latch does not necessarily mean that the lock
  	 * is free now, as there are many other sources for latch sets than
  	 * somebody releasing the lock.
  	 *
  	 * We process interrupts whenever the latch has been set, so cancel/die
  	 * interrupts are processed quickly. This means we must not mind losing
  	 * control to a cancel/die interrupt here.  We don't, because we have no
  	 * shared-state-change work to do after being granted the lock (the
  	 * grantor did it all).  We do have to worry about canceling the deadlock
  	 * timeout and updating the locallock table, but if we lose control to an
  	 * error, LockErrorCleanup will fix that up.
  	 */
  	do
  	{
  		if (InHotStandby)
  		{
  			/* Set a timer and wait for that or for the Lock to be granted */
  			ResolveRecoveryConflictWithLock(locallock->tag.lock);
  		}
  		else
  		{
  			WaitLatch(MyLatch, WL_LATCH_SET, 0,
  					  PG_WAIT_LOCK | locallock->tag.lock.locktag_type);
  			ResetLatch(MyLatch);
  			/* check for deadlocks first, as that's probably log-worthy */
  			if (got_deadlock_timeout)
  			{
  				CheckDeadLock();
  				got_deadlock_timeout = false;
  			}
  			CHECK_FOR_INTERRUPTS();
  		}
  
  		/*
  		 * waitStatus could change from STATUS_WAITING to something else
  		 * asynchronously.  Read it just once per loop to prevent surprising
  		 * behavior (such as missing log messages).
  		 */
  		myWaitStatus = *((volatile int *) &MyProc->waitStatus);
  
  		/*
  		 * If we are not deadlocked, but are waiting on an autovacuum-induced
  		 * task, send a signal to interrupt it.
  		 */
  		if (deadlock_state == DS_BLOCKED_BY_AUTOVACUUM && allow_autovacuum_cancel)
  		{
  			PGPROC	   *autovac = GetBlockingAutoVacuumPgproc();
  			PGXACT	   *autovac_pgxact = &ProcGlobal->allPgXact[autovac->pgprocno];
  
  			LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
  
  			/*
  			 * Only do it if the worker is not working to protect against Xid
  			 * wraparound.
  			 */
  			if ((autovac_pgxact->vacuumFlags & PROC_IS_AUTOVACUUM) &&
  				!(autovac_pgxact->vacuumFlags & PROC_VACUUM_FOR_WRAPAROUND))
  			{
  				int			pid = autovac->pid;
  				StringInfoData locktagbuf;
  				StringInfoData logbuf;	/* errdetail for server log */
  
  				initStringInfo(&locktagbuf);
  				initStringInfo(&logbuf);
  				DescribeLockTag(&locktagbuf, &lock->tag);
  				appendStringInfo(&logbuf,
  								 _("Process %d waits for %s on %s."),
  								 MyProcPid,
  								 GetLockmodeName(lock->tag.locktag_lockmethodid,
  												 lockmode),
  								 locktagbuf.data);
  
  				/* release lock as quickly as possible */
  				LWLockRelease(ProcArrayLock);
  
  				/* send the autovacuum worker Back to Old Kent Road */
  				ereport(DEBUG1,
  						(errmsg("sending cancel to blocking autovacuum PID %d",
  								pid),
  						 errdetail_log("%s", logbuf.data)));
  
  				if (kill(pid, SIGINT) < 0)
  				{
  					/*
  					 * There's a race condition here: once we release the
  					 * ProcArrayLock, it's possible for the autovac worker to
  					 * close up shop and exit before we can do the kill().
  					 * Therefore, we do not whinge about no-such-process.
  					 * Other errors such as EPERM could conceivably happen if
  					 * the kernel recycles the PID fast enough, but such cases
  					 * seem improbable enough that it's probably best to issue
  					 * a warning if we see some other errno.
  					 */
  					if (errno != ESRCH)
  						ereport(WARNING,
  								(errmsg("could not send signal to process %d: %m",
  										pid)));
  				}
  
  				pfree(logbuf.data);
  				pfree(locktagbuf.data);
  			}
  			else
  				LWLockRelease(ProcArrayLock);
  
  			/* prevent signal from being resent more than once */
  			allow_autovacuum_cancel = false;
  		}
  
  		/*
  		 * If awoken after the deadlock check interrupt has run, and
  		 * log_lock_waits is on, then report about the wait.
  		 */
  		if (log_lock_waits && deadlock_state != DS_NOT_YET_CHECKED)
  		{
  			StringInfoData buf,
  						lock_waiters_sbuf,
  						lock_holders_sbuf;
  			const char *modename;
  			long		secs;
  			int			usecs;
  			long		msecs;
  			SHM_QUEUE  *procLocks;
  			PROCLOCK   *proclock;
  			bool		first_holder = true,
  						first_waiter = true;
  			int			lockHoldersNum = 0;
  
  			initStringInfo(&buf);
  			initStringInfo(&lock_waiters_sbuf);
  			initStringInfo(&lock_holders_sbuf);
  
  			DescribeLockTag(&buf, &locallock->tag.lock);
  			modename = GetLockmodeName(locallock->tag.lock.locktag_lockmethodid,
  									   lockmode);
  			TimestampDifference(get_timeout_start_time(DEADLOCK_TIMEOUT),
  								GetCurrentTimestamp(),
  								&secs, &usecs);
  			msecs = secs * 1000 + usecs / 1000;
  			usecs = usecs % 1000;
  
  			/*
  			 * we loop over the lock's procLocks to gather a list of all
  			 * holders and waiters. Thus we will be able to provide more
  			 * detailed information for lock debugging purposes.
  			 *
  			 * lock->procLocks contains all processes which hold or wait for
  			 * this lock.
  			 */
  
  			LWLockAcquire(partitionLock, LW_SHARED);
  
  			procLocks = &(lock->procLocks);
  			proclock = (PROCLOCK *) SHMQueueNext(procLocks, procLocks,
  												 offsetof(PROCLOCK, lockLink));
  
  			while (proclock)
  			{
  				/*
  				 * we are a waiter if myProc->waitProcLock == proclock; we are
  				 * a holder if it is NULL or something different
  				 */
  				if (proclock->tag.myProc->waitProcLock == proclock)
  				{
  					if (first_waiter)
  					{
  						appendStringInfo(&lock_waiters_sbuf, "%d",
  										 proclock->tag.myProc->pid);
  						first_waiter = false;
  					}
  					else
  						appendStringInfo(&lock_waiters_sbuf, ", %d",
  										 proclock->tag.myProc->pid);
  				}
  				else
  				{
  					if (first_holder)
  					{
  						appendStringInfo(&lock_holders_sbuf, "%d",
  										 proclock->tag.myProc->pid);
  						first_holder = false;
  					}
  					else
  						appendStringInfo(&lock_holders_sbuf, ", %d",
  										 proclock->tag.myProc->pid);
  
  					lockHoldersNum++;
  				}
  
  				proclock = (PROCLOCK *) SHMQueueNext(procLocks, &proclock->lockLink,
  													 offsetof(PROCLOCK, lockLink));
  			}
  
  			LWLockRelease(partitionLock);
  
  			if (deadlock_state == DS_SOFT_DEADLOCK)
  				ereport(LOG,
  						(errmsg("process %d avoided deadlock for %s on %s by rearranging queue order after %ld.%03d ms",
  								MyProcPid, modename, buf.data, msecs, usecs),
  						 (errdetail_log_plural("Process holding the lock: %s. Wait queue: %s.",
  											   "Processes holding the lock: %s. Wait queue: %s.",
  											   lockHoldersNum, lock_holders_sbuf.data, lock_waiters_sbuf.data))));
  			else if (deadlock_state == DS_HARD_DEADLOCK)
  			{
  				/*
  				 * This message is a bit redundant with the error that will be
  				 * reported subsequently, but in some cases the error report
  				 * might not make it to the log (eg, if it's caught by an
  				 * exception handler), and we want to ensure all long-wait
  				 * events get logged.
  				 */
  				ereport(LOG,
  						(errmsg("process %d detected deadlock while waiting for %s on %s after %ld.%03d ms",
  								MyProcPid, modename, buf.data, msecs, usecs),
  						 (errdetail_log_plural("Process holding the lock: %s. Wait queue: %s.",
  											   "Processes holding the lock: %s. Wait queue: %s.",
  											   lockHoldersNum, lock_holders_sbuf.data, lock_waiters_sbuf.data))));
  			}
  
  			if (myWaitStatus == STATUS_WAITING)
  				ereport(LOG,
  						(errmsg("process %d still waiting for %s on %s after %ld.%03d ms",
  								MyProcPid, modename, buf.data, msecs, usecs),
  						 (errdetail_log_plural("Process holding the lock: %s. Wait queue: %s.",
  											   "Processes holding the lock: %s. Wait queue: %s.",
  											   lockHoldersNum, lock_holders_sbuf.data, lock_waiters_sbuf.data))));
  			else if (myWaitStatus == STATUS_OK)
  				ereport(LOG,
  						(errmsg("process %d acquired %s on %s after %ld.%03d ms",
  								MyProcPid, modename, buf.data, msecs, usecs)));
  			else
  			{
  				Assert(myWaitStatus == STATUS_ERROR);
  
  				/*
  				 * Currently, the deadlock checker always kicks its own
  				 * process, which means that we'll only see STATUS_ERROR when
  				 * deadlock_state == DS_HARD_DEADLOCK, and there's no need to
  				 * print redundant messages.  But for completeness and
  				 * future-proofing, print a message if it looks like someone
  				 * else kicked us off the lock.
  				 */
  				if (deadlock_state != DS_HARD_DEADLOCK)
  					ereport(LOG,
  							(errmsg("process %d failed to acquire %s on %s after %ld.%03d ms",
  									MyProcPid, modename, buf.data, msecs, usecs),
  							 (errdetail_log_plural("Process holding the lock: %s. Wait queue: %s.",
  												   "Processes holding the lock: %s. Wait queue: %s.",
  												   lockHoldersNum, lock_holders_sbuf.data, lock_waiters_sbuf.data))));
  			}
  
  			/*
  			 * At this point we might still need to wait for the lock. Reset
  			 * state so we don't print the above messages again.
  			 */
  			deadlock_state = DS_NO_DEADLOCK;
  
  			pfree(buf.data);
  			pfree(lock_holders_sbuf.data);
  			pfree(lock_waiters_sbuf.data);
  		}
  	} while (myWaitStatus == STATUS_WAITING);
  
  	/*
  	 * Disable the timers, if they are still running.  As in LockErrorCleanup,
  	 * we must preserve the LOCK_TIMEOUT indicator flag: if a lock timeout has
  	 * already caused QueryCancelPending to become set, we want the cancel to
  	 * be reported as a lock timeout, not a user cancel.
  	 */
  	if (!InHotStandby)
  	{
  		if (LockTimeout > 0)
  		{
  			DisableTimeoutParams timeouts[2];
  
  			timeouts[0].id = DEADLOCK_TIMEOUT;
  			timeouts[0].keep_indicator = false;
  			timeouts[1].id = LOCK_TIMEOUT;
  			timeouts[1].keep_indicator = true;
  			disable_timeouts(timeouts, 2);
  		}
  		else
  			disable_timeout(DEADLOCK_TIMEOUT, false);
  	}
  
  	/*
  	 * Re-acquire the lock table's partition lock.  We have to do this to hold
  	 * off cancel/die interrupts before we can mess with lockAwaited (else we
  	 * might have a missed or duplicated locallock update).
  	 */
  	LWLockAcquire(partitionLock, LW_EXCLUSIVE);
  
  	/*
  	 * We no longer want LockErrorCleanup to do anything.
  	 */
  	lockAwaited = NULL;
  
  	/*
  	 * If we got the lock, be sure to remember it in the locallock table.
  	 */
  	if (MyProc->waitStatus == STATUS_OK)
  		GrantAwaitedLock();
  
  	/*
  	 * We don't have to do anything else, because the awaker did all the
  	 * necessary update of the lock table and MyProc.
  	 */
  	return MyProc->waitStatus;
  }
  
  
  /*
   * ProcWakeup -- wake up a process by releasing its private semaphore.
   *
   *	 Also remove the process from the wait queue and set its links invalid.
   *	 RETURN: the next process in the wait queue.
   *
   * The appropriate lock partition lock must be held by caller.
   *
   * XXX: presently, this code is only used for the "success" case, and only
   * works correctly for that case.  To clean up in failure case, would need
   * to twiddle the lock's request counts too --- see RemoveFromWaitQueue.
   * Hence, in practice the waitStatus parameter must be STATUS_OK.
   */
  PGPROC *
  ProcWakeup(PGPROC *proc, int waitStatus)
  {
  	PGPROC	   *retProc;
  
  	/* Proc should be sleeping ... */
  	if (proc->links.prev == NULL ||
  		proc->links.next == NULL)
  		return NULL;
  	Assert(proc->waitStatus == STATUS_WAITING);
  
  	/* Save next process before we zap the list link */
  	retProc = (PGPROC *) proc->links.next;
  
  	/* Remove process from wait queue */
  	SHMQueueDelete(&(proc->links));
  	(proc->waitLock->waitProcs.size)--;
  
  	/* Clean up process' state and pass it the ok/fail signal */
  	proc->waitLock = NULL;
  	proc->waitProcLock = NULL;
  	proc->waitStatus = waitStatus;
  
  	/* And awaken it */
  	SetLatch(&proc->procLatch);
  
  	return retProc;
  }
  
  /*
   * ProcLockWakeup -- routine for waking up processes when a lock is
   *		released (or a prior waiter is aborted).  Scan all waiters
   *		for lock, waken any that are no longer blocked.
   *
   * The appropriate lock partition lock must be held by caller.
   */
  void
  ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock)
  {
  	PROC_QUEUE *waitQueue = &(lock->waitProcs);
  	int			queue_size = waitQueue->size;
  	PGPROC	   *proc;
  	LOCKMASK	aheadRequests = 0;
  
  	Assert(queue_size >= 0);
  
  	if (queue_size == 0)
  		return;
  
  	proc = (PGPROC *) waitQueue->links.next;
  
  	while (queue_size-- > 0)
  	{
  		LOCKMODE	lockmode = proc->waitLockMode;
  
  		/*
  		 * Waken if (a) doesn't conflict with requests of earlier waiters, and
  		 * (b) doesn't conflict with already-held locks.
  		 */
  		if ((lockMethodTable->conflictTab[lockmode] & aheadRequests) == 0 &&
  			LockCheckConflicts(lockMethodTable,
  							   lockmode,
  							   lock,
  							   proc->waitProcLock) == STATUS_OK)
  		{
  			/* OK to waken */
  			GrantLock(lock, proc->waitProcLock, lockmode);
  			proc = ProcWakeup(proc, STATUS_OK);
  
  			/*
  			 * ProcWakeup removes proc from the lock's waiting process queue
  			 * and returns the next proc in chain; don't use proc's next-link,
  			 * because it's been cleared.
  			 */
  		}
  		else
  		{
  			/*
  			 * Cannot wake this guy. Remember his request for later checks.
  			 */
  			aheadRequests |= LOCKBIT_ON(lockmode);
  			proc = (PGPROC *) proc->links.next;
  		}
  	}
  
  	Assert(waitQueue->size >= 0);
  }
  
  /*
   * CheckDeadLock
   *
   * We only get to this routine, if DEADLOCK_TIMEOUT fired while waiting for a
   * lock to be released by some other process.  Check if there's a deadlock; if
   * not, just return.  (But signal ProcSleep to log a message, if
   * log_lock_waits is true.)  If we have a real deadlock, remove ourselves from
   * the lock's wait queue and signal an error to ProcSleep.
   */
  static void
  CheckDeadLock(void)
  {
  	int			i;
  
  	/*
  	 * Acquire exclusive lock on the entire shared lock data structures. Must
  	 * grab LWLocks in partition-number order to avoid LWLock deadlock.
  	 *
  	 * Note that the deadlock check interrupt had better not be enabled
  	 * anywhere that this process itself holds lock partition locks, else this
  	 * will wait forever.  Also note that LWLockAcquire creates a critical
  	 * section, so that this routine cannot be interrupted by cancel/die
  	 * interrupts.
  	 */
  	for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
  		LWLockAcquire(LockHashPartitionLockByIndex(i), LW_EXCLUSIVE);
  
  	/*
  	 * Check to see if we've been awoken by anyone in the interim.
  	 *
  	 * If we have, we can return and resume our transaction -- happy day.
  	 * Before we are awoken the process releasing the lock grants it to us so
  	 * we know that we don't have to wait anymore.
  	 *
  	 * We check by looking to see if we've been unlinked from the wait queue.
  	 * This is quicker than checking our semaphore's state, since no kernel
  	 * call is needed, and it is safe because we hold the lock partition lock.
  	 */
  	if (MyProc->links.prev == NULL ||
  		MyProc->links.next == NULL)
  		goto check_done;
  
  #ifdef LOCK_DEBUG
  	if (Debug_deadlocks)
  		DumpAllLocks();
  #endif
  
  	/* Run the deadlock check, and set deadlock_state for use by ProcSleep */
  	deadlock_state = DeadLockCheck(MyProc);
  
  	if (deadlock_state == DS_HARD_DEADLOCK)
  	{
  		/*
  		 * Oops.  We have a deadlock.
  		 *
  		 * Get this process out of wait state. (Note: we could do this more
  		 * efficiently by relying on lockAwaited, but use this coding to
  		 * preserve the flexibility to kill some other transaction than the
  		 * one detecting the deadlock.)
  		 *
  		 * RemoveFromWaitQueue sets MyProc->waitStatus to STATUS_ERROR, so
  		 * ProcSleep will report an error after we return from the signal
  		 * handler.
  		 */
  		Assert(MyProc->waitLock != NULL);
  		RemoveFromWaitQueue(MyProc, LockTagHashCode(&(MyProc->waitLock->tag)));
  
  		/*
  		 * We're done here.  Transaction abort caused by the error that
  		 * ProcSleep will raise will cause any other locks we hold to be
  		 * released, thus allowing other processes to wake up; we don't need
  		 * to do that here.  NOTE: an exception is that releasing locks we
  		 * hold doesn't consider the possibility of waiters that were blocked
  		 * behind us on the lock we just failed to get, and might now be
  		 * wakable because we're not in front of them anymore.  However,
  		 * RemoveFromWaitQueue took care of waking up any such processes.
  		 */
  	}
  
  	/*
  	 * And release locks.  We do this in reverse order for two reasons: (1)
  	 * Anyone else who needs more than one of the locks will be trying to lock
  	 * them in increasing order; we don't want to release the other process
  	 * until it can get all the locks it needs. (2) This avoids O(N^2)
  	 * behavior inside LWLockRelease.
  	 */
  check_done:
  	for (i = NUM_LOCK_PARTITIONS; --i >= 0;)
  		LWLockRelease(LockHashPartitionLockByIndex(i));
  }
  
  /*
   * CheckDeadLockAlert - Handle the expiry of deadlock_timeout.
   *
   * NB: Runs inside a signal handler, be careful.
   */
  void
  CheckDeadLockAlert(void)
  {
  	int			save_errno = errno;
  
  	got_deadlock_timeout = true;
  
  	/*
  	 * Have to set the latch again, even if handle_sig_alarm already did. Back
  	 * then got_deadlock_timeout wasn't yet set... It's unlikely that this
  	 * ever would be a problem, but setting a set latch again is cheap.
  	 */
  	SetLatch(MyLatch);
  	errno = save_errno;
  }
  
  /*
   * ProcWaitForSignal - wait for a signal from another backend.
   *
   * As this uses the generic process latch the caller has to be robust against
   * unrelated wakeups: Always check that the desired state has occurred, and
   * wait again if not.
   */
  void
  ProcWaitForSignal(uint32 wait_event_info)
  {
  	WaitLatch(MyLatch, WL_LATCH_SET, 0, wait_event_info);
  	ResetLatch(MyLatch);
  	CHECK_FOR_INTERRUPTS();
  }
  
  /*
   * ProcSendSignal - send a signal to a backend identified by PID
   */
  void
  ProcSendSignal(int pid)
  {
  	PGPROC	   *proc = NULL;
  
  	if (RecoveryInProgress())
  	{
  		SpinLockAcquire(ProcStructLock);
  
  		/*
  		 * Check to see whether it is the Startup process we wish to signal.
  		 * This call is made by the buffer manager when it wishes to wake up a
  		 * process that has been waiting for a pin in so it can obtain a
  		 * cleanup lock using LockBufferForCleanup(). Startup is not a normal
  		 * backend, so BackendPidGetProc() will not return any pid at all. So
  		 * we remember the information for this special case.
  		 */
  		if (pid == ProcGlobal->startupProcPid)
  			proc = ProcGlobal->startupProc;
  
  		SpinLockRelease(ProcStructLock);
  	}
  
  	if (proc == NULL)
  		proc = BackendPidGetProc(pid);
  
  	if (proc != NULL)
  	{
  		SetLatch(&proc->procLatch);
  	}
  }
  
  /*
   * BecomeLockGroupLeader - designate process as lock group leader
   *
   * Once this function has returned, other processes can join the lock group
   * by calling BecomeLockGroupMember.
   */
  void
  BecomeLockGroupLeader(void)
  {
  	LWLock	   *leader_lwlock;
  
  	/* If we already did it, we don't need to do it again. */
  	if (MyProc->lockGroupLeader == MyProc)
  		return;
  
  	/* We had better not be a follower. */
  	Assert(MyProc->lockGroupLeader == NULL);
  
  	/* Create single-member group, containing only ourselves. */
  	leader_lwlock = LockHashPartitionLockByProc(MyProc);
  	LWLockAcquire(leader_lwlock, LW_EXCLUSIVE);
  	MyProc->lockGroupLeader = MyProc;
  	dlist_push_head(&MyProc->lockGroupMembers, &MyProc->lockGroupLink);
  	LWLockRelease(leader_lwlock);
  }
  
  /*
   * BecomeLockGroupMember - designate process as lock group member
   *
   * This is pretty straightforward except for the possibility that the leader
   * whose group we're trying to join might exit before we manage to do so;
   * and the PGPROC might get recycled for an unrelated process.  To avoid
   * that, we require the caller to pass the PID of the intended PGPROC as
   * an interlock.  Returns true if we successfully join the intended lock
   * group, and false if not.
   */
  bool
  BecomeLockGroupMember(PGPROC *leader, int pid)
  {
  	LWLock	   *leader_lwlock;
  	bool		ok = false;
  
  	/* Group leader can't become member of group */
  	Assert(MyProc != leader);
  
  	/* Can't already be a member of a group */
  	Assert(MyProc->lockGroupLeader == NULL);
  
  	/* PID must be valid. */
  	Assert(pid != 0);
  
  	/*
  	 * Get lock protecting the group fields.  Note LockHashPartitionLockByProc
  	 * accesses leader->pgprocno in a PGPROC that might be free.  This is safe
  	 * because all PGPROCs' pgprocno fields are set during shared memory
  	 * initialization and never change thereafter; so we will acquire the
  	 * correct lock even if the leader PGPROC is in process of being recycled.
  	 */
  	leader_lwlock = LockHashPartitionLockByProc(leader);
  	LWLockAcquire(leader_lwlock, LW_EXCLUSIVE);
  
  	/* Is this the leader we're looking for? */
  	if (leader->pid == pid && leader->lockGroupLeader == leader)
  	{
  		/* OK, join the group */
  		ok = true;
  		MyProc->lockGroupLeader = leader;
  		dlist_push_tail(&leader->lockGroupMembers, &MyProc->lockGroupLink);
  	}
  	LWLockRelease(leader_lwlock);
  
  	return ok;
  }
  