proc.c 38.0 KB
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/*-------------------------------------------------------------------------
 *
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 * proc.c
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 *	  routines to manage per-process shared memory data structure
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 *
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 * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
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 * Portions Copyright (c) 1994, Regents of the University of California
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 *
 *
 * IDENTIFICATION
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 *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.186 2007/03/07 13:35:03 alvherre Exp $
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 *
 *-------------------------------------------------------------------------
 */
/*
 * Interface (a):
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 *		ProcSleep(), ProcWakeup(),
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 *		ProcQueueAlloc() -- create a shm queue for sleeping processes
 *		ProcQueueInit() -- create a queue without allocing memory
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 *
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 * 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
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 * whether it was awoken on an error condition).
 *
 * Interface (b):
 *
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 * ProcReleaseLocks -- frees the locks associated with current transaction
 *
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 * ProcKill -- destroys the shared memory state (and locks)
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 * associated with the process.
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 */
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#include "postgres.h"

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#include <signal.h>
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#include <unistd.h>
#include <sys/time.h>
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#include "access/transam.h"
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#include "access/xact.h"
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#include "miscadmin.h"
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#include "postmaster/autovacuum.h"
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#include "storage/ipc.h"
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#include "storage/proc.h"
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#include "storage/procarray.h"
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#include "storage/spin.h"
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/* GUC variables */
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int			DeadlockTimeout = 1000;
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int			StatementTimeout = 0;
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bool		log_lock_waits = false;
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/* Pointer to this process's PGPROC struct, if any */
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PGPROC	   *MyProc = NULL;
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/*
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 * This spinlock protects the freelist of recycled PGPROC structures.
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 * We cannot use an LWLock because the LWLock manager depends on already
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 * having a PGPROC and a wait semaphore!  But these structures are touched
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 * relatively infrequently (only at backend startup or shutdown) and not for
 * very long, so a spinlock is okay.
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 */
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NON_EXEC_STATIC slock_t *ProcStructLock = NULL;
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/* Pointers to shared-memory structures */
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NON_EXEC_STATIC PROC_HDR *ProcGlobal = NULL;
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NON_EXEC_STATIC PGPROC *AuxiliaryProcs = NULL;
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/* If we are waiting for a lock, this points to the associated LOCALLOCK */
static LOCALLOCK *lockAwaited = NULL;
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/* Mark these volatile because they can be changed by signal handler */
static volatile bool statement_timeout_active = false;
static volatile bool deadlock_timeout_active = false;
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volatile bool cancel_from_timeout = false;
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/* statement_fin_time is valid only if statement_timeout_active is true */
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static TimestampTz statement_fin_time;
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static void RemoveProcFromArray(int code, Datum arg);
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static void ProcKill(int code, Datum arg);
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static void AuxiliaryProcKill(int code, Datum arg);
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static bool CheckStatementTimeout(void);
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/*
 * Report shared-memory space needed by InitProcGlobal.
 */
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Size
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ProcGlobalShmemSize(void)
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{
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	Size		size = 0;

	/* ProcGlobal */
	size = add_size(size, sizeof(PROC_HDR));
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	/* AuxiliaryProcs */
	size = add_size(size, mul_size(NUM_AUXILIARY_PROCS, sizeof(PGPROC)));
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	/* MyProcs */
	size = add_size(size, mul_size(MaxBackends, sizeof(PGPROC)));
	/* ProcStructLock */
	size = add_size(size, sizeof(slock_t));
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	return size;
}

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/*
 * Report number of semaphores needed by InitProcGlobal.
 */
int
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ProcGlobalSemas(void)
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{
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	/* We need a sema per backend, plus one for each auxiliary process. */
	return MaxBackends + NUM_AUXILIARY_PROCS;
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}

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/*
 * InitProcGlobal -
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 *	  Initialize the global process table during postmaster or standalone
 *	  backend startup.
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 *
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 *	  We also create all the per-process semaphores we will need to support
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 *	  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
 *	  MaxBackends higher than his kernel will support, he'll find out sooner
 *	  rather than later.
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 *
 *	  Another reason for creating semaphores here is that the semaphore
 *	  implementation typically requires us to create semaphores in the
 *	  postmaster, not in backends.
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 *
 * Note: this is NOT called by individual backends under a postmaster,
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 * not even in the EXEC_BACKEND case.  The ProcGlobal and AuxiliaryProcs
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 * pointers must be propagated specially for EXEC_BACKEND operation.
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 */
void
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InitProcGlobal(void)
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{
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	PGPROC	   *procs;
	int			i;
	bool		found;
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	/* Create the ProcGlobal shared structure */
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	ProcGlobal = (PROC_HDR *)
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		ShmemInitStruct("Proc Header", sizeof(PROC_HDR), &found);
	Assert(!found);
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	/*
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	 * Create the PGPROC structures for auxiliary (bgwriter) processes, too.
	 * These do not get linked into the freeProcs list.
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	 */
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	AuxiliaryProcs = (PGPROC *)
		ShmemInitStruct("AuxiliaryProcs", NUM_AUXILIARY_PROCS * sizeof(PGPROC),
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						&found);
	Assert(!found);
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	/*
	 * Initialize the data structures.
	 */
	ProcGlobal->freeProcs = INVALID_OFFSET;
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	ProcGlobal->spins_per_delay = DEFAULT_SPINS_PER_DELAY;
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	/*
	 * Pre-create the PGPROC structures and create a semaphore for each.
	 */
	procs = (PGPROC *) ShmemAlloc(MaxBackends * sizeof(PGPROC));
	if (!procs)
		ereport(FATAL,
				(errcode(ERRCODE_OUT_OF_MEMORY),
				 errmsg("out of shared memory")));
	MemSet(procs, 0, MaxBackends * sizeof(PGPROC));
	for (i = 0; i < MaxBackends; i++)
	{
		PGSemaphoreCreate(&(procs[i].sem));
		procs[i].links.next = ProcGlobal->freeProcs;
		ProcGlobal->freeProcs = MAKE_OFFSET(&procs[i]);
	}
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	MemSet(AuxiliaryProcs, 0, NUM_AUXILIARY_PROCS * sizeof(PGPROC));
	for (i = 0; i < NUM_AUXILIARY_PROCS; i++)
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	{
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		AuxiliaryProcs[i].pid = 0;	/* marks auxiliary proc as not in use */
		PGSemaphoreCreate(&(AuxiliaryProcs[i].sem));
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	}
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	/* Create ProcStructLock spinlock, too */
	ProcStructLock = (slock_t *) ShmemAlloc(sizeof(slock_t));
	SpinLockInit(ProcStructLock);
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}

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/*
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 * InitProcess -- initialize a per-process data structure for this backend
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 */
void
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InitProcess(void)
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{
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	/* use volatile pointer to prevent code rearrangement */
	volatile PROC_HDR *procglobal = ProcGlobal;
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	SHMEM_OFFSET myOffset;
	int			i;
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	/*
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	 * ProcGlobal should be set up already (if we are a backend, we inherit
	 * this by fork() or EXEC_BACKEND mechanism from the postmaster).
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	 */
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	if (procglobal == NULL)
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		elog(PANIC, "proc header uninitialized");
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	if (MyProc != NULL)
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		elog(ERROR, "you already exist");
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	/*
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	 * Try to get a proc struct from the free list.  If this fails, we must be
	 * out of PGPROC structures (not to mention semaphores).
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	 *
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	 * While we are holding the ProcStructLock, also copy the current shared
	 * estimate of spins_per_delay to local storage.
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	 */
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	SpinLockAcquire(ProcStructLock);
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	set_spins_per_delay(procglobal->spins_per_delay);

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	myOffset = procglobal->freeProcs;
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	if (myOffset != INVALID_OFFSET)
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	{
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		MyProc = (PGPROC *) MAKE_PTR(myOffset);
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		procglobal->freeProcs = MyProc->links.next;
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		SpinLockRelease(ProcStructLock);
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	}
	else
	{
		/*
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		 * 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.
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		 */
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		SpinLockRelease(ProcStructLock);
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		ereport(FATAL,
				(errcode(ERRCODE_TOO_MANY_CONNECTIONS),
				 errmsg("sorry, too many clients already")));
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	}
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	/*
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	 * Initialize all fields of MyProc, except for the semaphore which was
	 * prepared for us by InitProcGlobal.
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	 */
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	SHMQueueElemInit(&(MyProc->links));
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	MyProc->waitStatus = STATUS_OK;
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	MyProc->xid = InvalidTransactionId;
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	MyProc->xmin = InvalidTransactionId;
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	MyProc->pid = MyProcPid;
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	/* databaseId and roleId will be filled in later */
	MyProc->databaseId = InvalidOid;
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	MyProc->roleId = InvalidOid;
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	MyProc->inVacuum = false;
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	MyProc->isAutovacuum = IsAutoVacuumWorkerProcess();
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	MyProc->lwWaiting = false;
	MyProc->lwExclusive = false;
	MyProc->lwWaitLink = NULL;
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	MyProc->waitLock = NULL;
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	MyProc->waitProcLock = NULL;
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	for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
		SHMQueueInit(&(MyProc->myProcLocks[i]));
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	/*
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	 * We might be reusing a semaphore that belonged to a failed process. So
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	 * be careful and reinitialize its value here.	(This is not strictly
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	 * necessary anymore, but seems like a good idea for cleanliness.)
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	 */
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	PGSemaphoreReset(&MyProc->sem);
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	/*
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	 * Arrange to clean up at backend exit.
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	 */
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	on_shmem_exit(ProcKill, 0);
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	/*
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	 * Now that we have a PGPROC, we could try to acquire locks, so initialize
	 * the deadlock checker.
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	 */
	InitDeadLockChecking();
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}

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/*
 * 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 there is a good deal
 * of stuff to be done before this step that will require LWLock access.
 */
void
InitProcessPhase2(void)
{
	Assert(MyProc != NULL);

	/*
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	 * We should now know what database we're in, so advertise that.  (We need
	 * not do any locking here, since no other backend can yet see our
	 * PGPROC.)
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	 */
	Assert(OidIsValid(MyDatabaseId));
	MyProc->databaseId = MyDatabaseId;

	/*
	 * 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);
}

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/*
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 * InitAuxiliaryProcess -- create a per-auxiliary-process data structure
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 *
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 * 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
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 * and sema that are assigned are one of the extra ones created during
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 * InitProcGlobal.
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 *
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 * Auxiliary processes are presently not expected to wait for real (lockmgr)
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 * locks, so we need not set up the deadlock checker.  They are never added
 * to the ProcArray or the sinval messaging mechanism, either.
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 */
void
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InitAuxiliaryProcess(void)
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{
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	PGPROC	   *auxproc;
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	int			proctype;
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	int			i;
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	/*
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	 * ProcGlobal should be set up already (if we are a backend, we inherit
	 * this by fork() or EXEC_BACKEND mechanism from the postmaster).
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	 */
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	if (ProcGlobal == NULL || AuxiliaryProcs == NULL)
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		elog(PANIC, "proc header uninitialized");
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	if (MyProc != NULL)
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		elog(ERROR, "you already exist");
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	/*
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	 * We use the ProcStructLock to protect assignment and releasing of
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	 * AuxiliaryProcs entries.
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	 *
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	 * While we are holding the ProcStructLock, also copy the current shared
	 * estimate of spins_per_delay to local storage.
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	 */
	SpinLockAcquire(ProcStructLock);

	set_spins_per_delay(ProcGlobal->spins_per_delay);

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	/*
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	 * Find a free auxproc ... *big* trouble if there isn't one ...
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	 */
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	for (proctype = 0; proctype < NUM_AUXILIARY_PROCS; proctype++)
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	{
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		auxproc = &AuxiliaryProcs[proctype];
		if (auxproc->pid == 0)
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			break;
	}
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	if (proctype >= NUM_AUXILIARY_PROCS)
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	{
		SpinLockRelease(ProcStructLock);
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		elog(FATAL, "all AuxiliaryProcs are in use");
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	}
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	/* Mark auxiliary proc as in use by me */
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	/* use volatile pointer to prevent code rearrangement */
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	((volatile PGPROC *) auxproc)->pid = MyProcPid;
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	MyProc = auxproc;
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	SpinLockRelease(ProcStructLock);

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	/*
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	 * Initialize all fields of MyProc, except for the semaphore which was
	 * prepared for us by InitProcGlobal.
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	 */
	SHMQueueElemInit(&(MyProc->links));
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	MyProc->waitStatus = STATUS_OK;
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	MyProc->xid = InvalidTransactionId;
	MyProc->xmin = InvalidTransactionId;
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	MyProc->databaseId = InvalidOid;
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	MyProc->roleId = InvalidOid;
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	MyProc->inVacuum = false;
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	MyProc->isAutovacuum = IsAutoVacuumLauncherProcess(); /* is this needed? */
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	MyProc->lwWaiting = false;
	MyProc->lwExclusive = false;
	MyProc->lwWaitLink = NULL;
	MyProc->waitLock = NULL;
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	MyProc->waitProcLock = NULL;
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	for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
		SHMQueueInit(&(MyProc->myProcLocks[i]));
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	/*
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	 * We might be reusing a semaphore that belonged to a failed process. So
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	 * be careful and reinitialize its value here.	(This is not strictly
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	 * necessary anymore, but seems like a good idea for cleanliness.)
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	 */
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	PGSemaphoreReset(&MyProc->sem);
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	/*
	 * Arrange to clean up at process exit.
	 */
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	on_shmem_exit(AuxiliaryProcKill, Int32GetDatum(proctype));
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}

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/*
 * 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)
{
	SHMEM_OFFSET offset;
	PGPROC	   *proc;
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	/* use volatile pointer to prevent code rearrangement */
	volatile PROC_HDR *procglobal = ProcGlobal;

	SpinLockAcquire(ProcStructLock);

	offset = procglobal->freeProcs;

	while (n > 0 && offset != INVALID_OFFSET)
	{
		proc = (PGPROC *) MAKE_PTR(offset);
		offset = proc->links.next;
		n--;
	}

	SpinLockRelease(ProcStructLock);

	return (n <= 0);
}

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/*
 * Cancel any pending wait for lock, when aborting a transaction.
 *
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 * Returns true if we had been waiting for a lock, else false.
 *
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 * (Normally, this would only happen if we accept a cancel/die
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 * interrupt while waiting; but an ereport(ERROR) while waiting is
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 * within the realm of possibility, too.)
 */
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bool
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LockWaitCancel(void)
{
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	LWLockId	partitionLock;

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	/* Nothing to do if we weren't waiting for a lock */
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	if (lockAwaited == NULL)
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		return false;

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	/* Turn off the deadlock timer, if it's still running (see ProcSleep) */
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	disable_sig_alarm(false);
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	/* Unlink myself from the wait queue, if on it (might not be anymore!) */
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	partitionLock = LockHashPartitionLock(lockAwaited->hashcode);
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	LWLockAcquire(partitionLock, LW_EXCLUSIVE);
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	if (MyProc->links.next != INVALID_OFFSET)
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	{
		/* We could not have been granted the lock yet */
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		RemoveFromWaitQueue(MyProc, lockAwaited->hashcode);
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	}
	else
	{
		/*
		 * Somebody kicked us off the lock queue already.  Perhaps they
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		 * 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.
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		 */
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		if (MyProc->waitStatus == STATUS_OK)
			GrantAwaitedLock();
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	}

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	lockAwaited = NULL;
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	LWLockRelease(partitionLock);
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	/*
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	 * We used to do PGSemaphoreReset() here to ensure that our proc's wait
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	 * semaphore is reset to zero.	This prevented a leftover wakeup signal
	 * from remaining in the semaphore if someone else had granted us the lock
	 * we wanted before we were able to remove ourselves from the wait-list.
	 * However, now that ProcSleep loops until waitStatus changes, a leftover
	 * wakeup signal isn't harmful, and it seems not worth expending cycles to
	 * get rid of a signal that most likely isn't there.
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	 */
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	/*
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	 * Return true even if we were kicked off the lock before we were able to
	 * remove ourselves.
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	 */
	return true;
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}
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/*
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 * ProcReleaseLocks() -- release locks associated with current transaction
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 *			at main transaction commit or abort
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 *
 * At main transaction commit, we release all locks except session locks.
 * At main transaction abort, we release all locks including session locks;
 * this lets us clean up after a VACUUM FULL failure.
 *
 * At subtransaction commit, we don't release any locks (so this func is not
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 * needed at all); we will defer the releasing to the parent transaction.
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 * At subtransaction abort, we release all locks held by the subtransaction;
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 * this is implemented by retail releasing of the locks under control of
 * the ResourceOwner mechanism.
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 *
 * Note that user locks are not released in any case.
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 */
void
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ProcReleaseLocks(bool isCommit)
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{
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	if (!MyProc)
		return;
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	/* If waiting, get off wait queue (should only be needed after error) */
	LockWaitCancel();
	/* Release locks */
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	LockReleaseAll(DEFAULT_LOCKMETHOD, !isCommit);
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}


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/*
 * RemoveProcFromArray() -- Remove this process from the shared ProcArray.
 */
static void
RemoveProcFromArray(int code, Datum arg)
{
	Assert(MyProc != NULL);
	ProcArrayRemove(MyProc);
}

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/*
 * ProcKill() -- Destroy the per-proc data structure for
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 *		this process. Release any of its held LW locks.
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 */
static void
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ProcKill(int code, Datum arg)
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{
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	/* use volatile pointer to prevent code rearrangement */
	volatile PROC_HDR *procglobal = ProcGlobal;

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	Assert(MyProc != NULL);
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	/*
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	 * 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
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	 * facility by releasing our PGPROC ...
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	 */
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	LWLockReleaseAll();
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	SpinLockAcquire(ProcStructLock);
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	/* Return PGPROC structure (and semaphore) to freelist */
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	MyProc->links.next = procglobal->freeProcs;
	procglobal->freeProcs = MAKE_OFFSET(MyProc);
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	/* PGPROC struct isn't mine anymore */
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	MyProc = NULL;
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	/* Update shared estimate of spins_per_delay */
	procglobal->spins_per_delay = update_spins_per_delay(procglobal->spins_per_delay);

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	SpinLockRelease(ProcStructLock);
}

/*
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 * AuxiliaryProcKill() -- Cut-down version of ProcKill for auxiliary
 *		processes (bgwriter, etc).	The PGPROC and sema are not released, only
 *		marked as not-in-use.
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 */
static void
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AuxiliaryProcKill(int code, Datum arg)
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{
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	int			proctype = DatumGetInt32(arg);
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	PGPROC	   *auxproc;
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	Assert(proctype >= 0 && proctype < NUM_AUXILIARY_PROCS);
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	auxproc = &AuxiliaryProcs[proctype];
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	Assert(MyProc == auxproc);
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	/* Release any LW locks I am holding (see notes above) */
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	LWLockReleaseAll();

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	SpinLockAcquire(ProcStructLock);

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	/* Mark auxiliary proc no longer in use */
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	MyProc->pid = 0;

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	/* PGPROC struct isn't mine anymore */
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	MyProc = NULL;
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	/* Update shared estimate of spins_per_delay */
	ProcGlobal->spins_per_delay = update_spins_per_delay(ProcGlobal->spins_per_delay);

	SpinLockRelease(ProcStructLock);
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}

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/*
 * ProcQueue package: routines for putting processes to sleep
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 *		and  waking them up
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 */

/*
 * ProcQueueAlloc -- alloc/attach to a shared memory process queue
 *
 * Returns: a pointer to the queue or NULL
 * Side Effects: Initializes the queue if we allocated one
 */
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#ifdef NOT_USED
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PROC_QUEUE *
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ProcQueueAlloc(char *name)
{
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	bool		found;
	PROC_QUEUE *queue = (PROC_QUEUE *)
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	ShmemInitStruct(name, sizeof(PROC_QUEUE), &found);
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	if (!queue)
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		return NULL;
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	if (!found)
		ProcQueueInit(queue);
642
	return queue;
643
}
644
#endif
645 646 647 648 649

/*
 * ProcQueueInit -- initialize a shared memory process queue
 */
void
650
ProcQueueInit(PROC_QUEUE *queue)
651
{
652 653
	SHMQueueInit(&(queue->links));
	queue->size = 0;
654 655 656 657
}


/*
658
 * ProcSleep -- put a process to sleep on the specified lock
659
 *
660 661
 * Caller must have set MyProc->heldLocks to reflect locks already held
 * on the lockable object by this process (under all XIDs).
662
 *
663
 * The lock table's partition lock must be held at entry, and will be held
664
 * at exit.
665
 *
666
 * Result: STATUS_OK if we acquired the lock, STATUS_ERROR if not (deadlock).
667
 *
668
 * ASSUME: that no one will fiddle with the queue until after
669
 *		we release the partition lock.
670 671
 *
 * NOTES: The process queue is now a priority queue for locking.
672 673 674
 *
 * P() on the semaphore should put us to sleep.  The process
 * semaphore is normally zero, so when we try to acquire it, we sleep.
675 676
 */
int
677
ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
678
{
679 680 681
	LOCKMODE	lockmode = locallock->tag.mode;
	LOCK	   *lock = locallock->lock;
	PROCLOCK   *proclock = locallock->proclock;
682 683
	uint32		hashcode = locallock->hashcode;
	LWLockId	partitionLock = LockHashPartitionLock(hashcode);
684
	PROC_QUEUE *waitQueue = &(lock->waitProcs);
685
	LOCKMASK	myHeldLocks = MyProc->heldLocks;
686
	bool		early_deadlock = false;
J
Jan Wieck 已提交
687
	PGPROC	   *proc;
688
	int			i;
689

690
	/*
691 692
	 * Determine where to add myself in the wait queue.
	 *
693 694 695 696
	 * 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
B
Bruce Momjian 已提交
697 698
	 * waiter anyway; but it's relatively cheap to detect such a conflict
	 * immediately, and avoid delaying till deadlock timeout.
699
	 *
700 701
	 * 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
B
Bruce Momjian 已提交
702 703 704 705
	 * 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.
706 707
	 */
	if (myHeldLocks != 0)
V
Vadim B. Mikheev 已提交
708
	{
709
		LOCKMASK	aheadRequests = 0;
710

J
Jan Wieck 已提交
711
		proc = (PGPROC *) MAKE_PTR(waitQueue->links.next);
712
		for (i = 0; i < waitQueue->size; i++)
V
Vadim B. Mikheev 已提交
713
		{
714
			/* Must he wait for me? */
B
Bruce Momjian 已提交
715
			if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks)
V
Vadim B. Mikheev 已提交
716
			{
717
				/* Must I wait for him ? */
B
Bruce Momjian 已提交
718
				if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks)
719
				{
720
					/*
B
Bruce Momjian 已提交
721 722 723 724 725
					 * 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.
726
					 */
727
					RememberSimpleDeadLock(MyProc, lockmode, lock, proc);
728 729
					early_deadlock = true;
					break;
730
				}
731
				/* I must go before this waiter.  Check special case. */
B
Bruce Momjian 已提交
732
				if ((lockMethodTable->conflictTab[lockmode] & aheadRequests) == 0 &&
733 734 735
					LockCheckConflicts(lockMethodTable,
									   lockmode,
									   lock,
736
									   proclock,
737
									   MyProc) == STATUS_OK)
738
				{
739
					/* Skip the wait and just grant myself the lock. */
740
					GrantLock(lock, proclock, lockmode);
741
					GrantAwaitedLock();
742
					return STATUS_OK;
743 744
				}
				/* Break out of loop to put myself before him */
V
Vadim B. Mikheev 已提交
745
				break;
746
			}
747
			/* Nope, so advance to next waiter */
748
			aheadRequests |= LOCKBIT_ON(proc->waitLockMode);
J
Jan Wieck 已提交
749
			proc = (PGPROC *) MAKE_PTR(proc->links.next);
V
Vadim B. Mikheev 已提交
750
		}
B
Bruce Momjian 已提交
751

752
		/*
B
Bruce Momjian 已提交
753 754
		 * If we fall out of loop normally, proc points to waitQueue head, so
		 * we will insert at tail of queue as desired.
755
		 */
756 757 758 759
	}
	else
	{
		/* I hold no locks, so I can't push in front of anyone. */
J
Jan Wieck 已提交
760
		proc = (PGPROC *) &(waitQueue->links);
V
Vadim B. Mikheev 已提交
761
	}
762

763
	/*
B
Bruce Momjian 已提交
764
	 * Insert self into queue, ahead of the given proc (or at tail of queue).
765
	 */
766
	SHMQueueInsertBefore(&(proc->links), &(MyProc->links));
B
Bruce Momjian 已提交
767
	waitQueue->size++;
768

769
	lock->waitMask |= LOCKBIT_ON(lockmode);
770

J
Jan Wieck 已提交
771
	/* Set up wait information in PGPROC object, too */
772
	MyProc->waitLock = lock;
773
	MyProc->waitProcLock = proclock;
774 775
	MyProc->waitLockMode = lockmode;

776
	MyProc->waitStatus = STATUS_WAITING;
777 778

	/*
B
Bruce Momjian 已提交
779 780 781
	 * 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.
782 783 784
	 */
	if (early_deadlock)
	{
785
		RemoveFromWaitQueue(MyProc, hashcode);
786 787
		return STATUS_ERROR;
	}
788

789
	/* mark that we are waiting for a lock */
790
	lockAwaited = locallock;
791

792
	/*
793
	 * Release the lock table's partition lock.
794
	 *
795
	 * NOTE: this may also cause us to exit critical-section state, possibly
B
Bruce Momjian 已提交
796 797
	 * 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
798
	 * LockWaitCancel will clean up if cancel/die happens.
799
	 */
800
	LWLockRelease(partitionLock);
801

802
	/*
B
Bruce Momjian 已提交
803 804 805 806
	 * 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.
807
	 *
808 809
	 * By delaying the check until we've waited for a bit, we can avoid
	 * running the rather expensive deadlock-check code in most cases.
810
	 */
811
	if (!enable_sig_alarm(DeadlockTimeout, false))
812
		elog(FATAL, "could not set timer for process wakeup");
813

814
	/*
815
	 * If someone wakes us between LWLockRelease and PGSemaphoreLock,
B
Bruce Momjian 已提交
816
	 * PGSemaphoreLock will not block.	The wakeup is "saved" by the semaphore
B
Bruce Momjian 已提交
817 818 819 820 821
	 * implementation.	While this is normally good, there are cases where a
	 * saved wakeup might be leftover from a previous operation (for example,
	 * we aborted ProcWaitForSignal just before someone did ProcSendSignal).
	 * So, loop to wait again if the waitStatus shows we haven't been granted
	 * nor denied the lock yet.
822
	 *
823 824 825 826 827 828 829
	 * We pass interruptOK = true, which eliminates a window in which
	 * cancel/die interrupts would be held off undesirably.  This is a promise
	 * that we don't 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
	 * updating the locallock table, but if we lose control to an error,
	 * LockWaitCancel will fix that up.
830
	 */
B
Bruce Momjian 已提交
831 832
	do
	{
833 834
		PGSemaphoreLock(&MyProc->sem, true);
	} while (MyProc->waitStatus == STATUS_WAITING);
835

836
	/*
837
	 * Disable the timer, if it's still running
B
Bruce Momjian 已提交
838
	 */
839
	if (!disable_sig_alarm(false))
840
		elog(FATAL, "could not disable timer for process wakeup");
B
Bruce Momjian 已提交
841

842
	/*
B
Bruce Momjian 已提交
843 844 845
	 * 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).
846
	 */
847
	LWLockAcquire(partitionLock, LW_EXCLUSIVE);
848 849 850

	/*
	 * We no longer want LockWaitCancel to do anything.
851
	 */
852
	lockAwaited = NULL;
853

854
	/*
855
	 * If we got the lock, be sure to remember it in the locallock table.
856
	 */
857
	if (MyProc->waitStatus == STATUS_OK)
858
		GrantAwaitedLock();
859

860 861 862 863
	/*
	 * We don't have to do anything else, because the awaker did all the
	 * necessary update of the lock table and MyProc.
	 */
864
	return MyProc->waitStatus;
865 866 867 868 869 870
}


/*
 * ProcWakeup -- wake up a process by releasing its private semaphore.
 *
871
 *	 Also remove the process from the wait queue and set its links invalid.
872
 *	 RETURN: the next process in the wait queue.
873
 *
874 875
 * The appropriate lock partition lock must be held by caller.
 *
876 877 878
 * 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.
879
 * Hence, in practice the waitStatus parameter must be STATUS_OK.
880
 */
J
Jan Wieck 已提交
881
PGPROC *
882
ProcWakeup(PGPROC *proc, int waitStatus)
883
{
J
Jan Wieck 已提交
884
	PGPROC	   *retProc;
885

886
	/* Proc should be sleeping ... */
887 888
	if (proc->links.prev == INVALID_OFFSET ||
		proc->links.next == INVALID_OFFSET)
889
		return NULL;
890
	Assert(proc->waitStatus == STATUS_WAITING);
891

892
	/* Save next process before we zap the list link */
J
Jan Wieck 已提交
893
	retProc = (PGPROC *) MAKE_PTR(proc->links.next);
894

895
	/* Remove process from wait queue */
896
	SHMQueueDelete(&(proc->links));
897
	(proc->waitLock->waitProcs.size)--;
898

899 900
	/* Clean up process' state and pass it the ok/fail signal */
	proc->waitLock = NULL;
901
	proc->waitProcLock = NULL;
902
	proc->waitStatus = waitStatus;
903

904
	/* And awaken it */
905
	PGSemaphoreUnlock(&proc->sem);
906 907

	return retProc;
908 909 910 911
}

/*
 * ProcLockWakeup -- routine for waking up processes when a lock is
912 913
 *		released (or a prior waiter is aborted).  Scan all waiters
 *		for lock, waken any that are no longer blocked.
914 915
 *
 * The appropriate lock partition lock must be held by caller.
916
 */
917
void
918
ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock)
919
{
920 921
	PROC_QUEUE *waitQueue = &(lock->waitProcs);
	int			queue_size = waitQueue->size;
J
Jan Wieck 已提交
922
	PGPROC	   *proc;
923
	LOCKMASK	aheadRequests = 0;
M
 
Marc G. Fournier 已提交
924

925
	Assert(queue_size >= 0);
926

927 928
	if (queue_size == 0)
		return;
929

J
Jan Wieck 已提交
930
	proc = (PGPROC *) MAKE_PTR(waitQueue->links.next);
931

932 933
	while (queue_size-- > 0)
	{
B
Bruce Momjian 已提交
934
		LOCKMODE	lockmode = proc->waitLockMode;
M
 
Marc G. Fournier 已提交
935 936

		/*
B
Bruce Momjian 已提交
937 938
		 * Waken if (a) doesn't conflict with requests of earlier waiters, and
		 * (b) doesn't conflict with already-held locks.
M
 
Marc G. Fournier 已提交
939
		 */
B
Bruce Momjian 已提交
940
		if ((lockMethodTable->conflictTab[lockmode] & aheadRequests) == 0 &&
941 942 943
			LockCheckConflicts(lockMethodTable,
							   lockmode,
							   lock,
944
							   proc->waitProcLock,
945
							   proc) == STATUS_OK)
M
 
Marc G. Fournier 已提交
946
		{
947
			/* OK to waken */
948
			GrantLock(lock, proc->waitProcLock, lockmode);
949
			proc = ProcWakeup(proc, STATUS_OK);
B
Bruce Momjian 已提交
950

951
			/*
B
Bruce Momjian 已提交
952 953 954
			 * 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.
955
			 */
M
 
Marc G. Fournier 已提交
956
		}
957
		else
958
		{
B
Bruce Momjian 已提交
959
			/*
B
Bruce Momjian 已提交
960
			 * Cannot wake this guy. Remember his request for later checks.
B
Bruce Momjian 已提交
961
			 */
962
			aheadRequests |= LOCKBIT_ON(lockmode);
J
Jan Wieck 已提交
963
			proc = (PGPROC *) MAKE_PTR(proc->links.next);
964
		}
M
 
Marc G. Fournier 已提交
965
	}
966 967

	Assert(waitQueue->size >= 0);
968 969
}

970 971 972
/*
 * CheckDeadLock
 *
973
 * We only get to this routine if we got SIGALRM after DeadlockTimeout
974 975 976 977
 * while waiting for a lock to be released by some other process.  Look
 * to see if there's a deadlock; if not, just return and continue waiting.
 * If we have a real deadlock, remove ourselves from the lock's wait queue
 * and signal an error to ProcSleep.
978
 */
979
static void
980
CheckDeadLock(void)
981
{
982
	int			i;
983
	DeadlockState deadlock_state = DS_DEADLOCK_NOT_FOUND;
984

985
	/*
B
Bruce Momjian 已提交
986 987
	 * Acquire exclusive lock on the entire shared lock data structures. Must
	 * grab LWLocks in partition-number order to avoid LWLock deadlock.
988 989 990 991 992 993
	 *
	 * 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.
994
	 */
995 996
	for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
		LWLockAcquire(FirstLockMgrLock + i, LW_EXCLUSIVE);
997

998
	/*
999 1000
	 * Check to see if we've been awoken by anyone in the interim.
	 *
1001 1002 1003
	 * 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.
1004
	 *
1005
	 * We check by looking to see if we've been unlinked from the wait queue.
B
Bruce Momjian 已提交
1006
	 * This is quicker than checking our semaphore's state, since no kernel
1007
	 * call is needed, and it is safe because we hold the lock partition lock.
1008
	 */
1009 1010 1011 1012 1013
	if (MyProc->links.prev != INVALID_OFFSET &&
		MyProc->links.next != INVALID_OFFSET)
		deadlock_state = DeadLockCheck(MyProc);
	
	if (deadlock_state == DS_HARD_DEADLOCK)
B
Bruce Momjian 已提交
1014
	{
1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027
		/*
		 * 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)));
1028

1029 1030 1031 1032 1033
		/*
		 * Unlock my semaphore so that the interrupted ProcSleep() call can
		 * finish.
		 */
		PGSemaphoreUnlock(&MyProc->sem);
1034

1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045
		/*
		 * 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.
		 */
	}
1046 1047

	/*
B
Bruce Momjian 已提交
1048 1049
	 * Release locks acquired at head of routine.  Order is not critical, so
	 * do it back-to-front to avoid waking another CheckDeadLock instance
1050 1051
	 * before it can get all the locks.
	 */
B
Bruce Momjian 已提交
1052
	for (i = NUM_LOCK_PARTITIONS; --i >= 0;)
1053
		LWLockRelease(FirstLockMgrLock + i);
1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079

	/*
	 * Issue any log messages requested.
	 *
	 * Deadlock ERROR messages are issued as part of transaction abort, so 
	 * these messages should not raise error states intentionally.
	 */
	if (log_lock_waits)
	{
		switch (deadlock_state)
		{
			case DS_SOFT_DEADLOCK:
				ereport(LOG,
					(errmsg("deadlock avoided by rearranging lock order")));
				break;
			case DS_DEADLOCK_NOT_FOUND:
				ereport(LOG,
					(errmsg("statement waiting for lock for at least %d ms",
								DeadlockTimeout)));
				break;
			case DS_HARD_DEADLOCK:
				break;	/* ERROR message handled during abort */
			default:
				break;
		}
	}
1080 1081 1082
}


1083 1084 1085 1086 1087 1088
/*
 * ProcWaitForSignal - wait for a signal from another backend.
 *
 * This can share the semaphore normally used for waiting for locks,
 * since a backend could never be waiting for a lock and a signal at
 * the same time.  As with locks, it's OK if the signal arrives just
B
Bruce Momjian 已提交
1089
 * before we actually reach the waiting state.	Also as with locks,
1090 1091
 * it's necessary that the caller be robust against bogus wakeups:
 * always check that the desired state has occurred, and wait again
B
Bruce Momjian 已提交
1092
 * if not.	This copes with possible "leftover" wakeups.
1093 1094 1095 1096
 */
void
ProcWaitForSignal(void)
{
1097
	PGSemaphoreLock(&MyProc->sem, true);
1098 1099 1100
}

/*
1101
 * ProcSendSignal - send a signal to a backend identified by PID
1102 1103
 */
void
1104
ProcSendSignal(int pid)
1105
{
1106
	PGPROC	   *proc = BackendPidGetProc(pid);
1107 1108

	if (proc != NULL)
1109
		PGSemaphoreUnlock(&proc->sem);
1110 1111 1112
}


1113 1114 1115 1116 1117 1118 1119 1120 1121
/*****************************************************************************
 * SIGALRM interrupt support
 *
 * Maybe these should be in pqsignal.c?
 *****************************************************************************/

/*
 * Enable the SIGALRM interrupt to fire after the specified delay
 *
1122
 * Delay is given in milliseconds.	Caller should be sure a SIGALRM
1123 1124
 * signal handler is installed before this is called.
 *
1125 1126
 * This code properly handles nesting of deadlock timeout alarms within
 * statement timeout alarms.
1127
 *
1128 1129 1130
 * Returns TRUE if okay, FALSE on failure.
 */
bool
1131
enable_sig_alarm(int delayms, bool is_statement_timeout)
1132
{
1133
	TimestampTz fin_time;
1134
	struct itimerval timeval;
1135

1136 1137
	if (is_statement_timeout)
	{
1138 1139 1140 1141 1142 1143 1144 1145 1146 1147
		/*
		 * Begin statement-level timeout
		 *
		 * Note that we compute statement_fin_time with reference to the
		 * statement_timestamp, but apply the specified delay without any
		 * correction; that is, we ignore whatever time has elapsed since
		 * statement_timestamp was set.  In the normal case only a small
		 * interval will have elapsed and so this doesn't matter, but there
		 * are corner cases (involving multi-statement query strings with
		 * embedded COMMIT or ROLLBACK) where we might re-initialize the
B
Bruce Momjian 已提交
1148 1149 1150 1151
		 * statement timeout long after initial receipt of the message. In
		 * such cases the enforcement of the statement timeout will be a bit
		 * inconsistent.  This annoyance is judged not worth the cost of
		 * performing an additional gettimeofday() here.
1152
		 */
1153
		Assert(!deadlock_timeout_active);
1154 1155
		fin_time = GetCurrentStatementStartTimestamp();
		fin_time = TimestampTzPlusMilliseconds(fin_time, delayms);
1156
		statement_fin_time = fin_time;
1157
		cancel_from_timeout = false;
1158
		statement_timeout_active = true;
1159 1160 1161 1162 1163 1164
	}
	else if (statement_timeout_active)
	{
		/*
		 * Begin deadlock timeout with statement-level timeout active
		 *
1165 1166 1167 1168
		 * Here, we want to interrupt at the closer of the two timeout times.
		 * If fin_time >= statement_fin_time then we need not touch the
		 * existing timer setting; else set up to interrupt at the deadlock
		 * timeout time.
1169 1170 1171
		 *
		 * NOTE: in this case it is possible that this routine will be
		 * interrupted by the previously-set timer alarm.  This is okay
B
Bruce Momjian 已提交
1172 1173 1174
		 * because the signal handler will do only what it should do according
		 * to the state variables.	The deadlock checker may get run earlier
		 * than normal, but that does no harm.
1175
		 */
1176 1177
		fin_time = GetCurrentTimestamp();
		fin_time = TimestampTzPlusMilliseconds(fin_time, delayms);
1178
		deadlock_timeout_active = true;
1179
		if (fin_time >= statement_fin_time)
1180 1181 1182 1183 1184 1185 1186
			return true;
	}
	else
	{
		/* Begin deadlock timeout with no statement-level timeout */
		deadlock_timeout_active = true;
	}
1187

1188
	/* If we reach here, okay to set the timer interrupt */
1189
	MemSet(&timeval, 0, sizeof(struct itimerval));
1190 1191
	timeval.it_value.tv_sec = delayms / 1000;
	timeval.it_value.tv_usec = (delayms % 1000) * 1000;
1192
	if (setitimer(ITIMER_REAL, &timeval, NULL))
1193
		return false;
1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214
	return true;
}

/*
 * Cancel the SIGALRM timer, either for a deadlock timeout or a statement
 * timeout.  If a deadlock timeout is canceled, any active statement timeout
 * remains in force.
 *
 * Returns TRUE if okay, FALSE on failure.
 */
bool
disable_sig_alarm(bool is_statement_timeout)
{
	/*
	 * Always disable the interrupt if it is active; this avoids being
	 * interrupted by the signal handler and thereby possibly getting
	 * confused.
	 *
	 * We will re-enable the interrupt if necessary in CheckStatementTimeout.
	 */
	if (statement_timeout_active || deadlock_timeout_active)
1215
	{
1216
		struct itimerval timeval;
1217

1218
		MemSet(&timeval, 0, sizeof(struct itimerval));
1219
		if (setitimer(ITIMER_REAL, &timeval, NULL))
1220
		{
1221 1222 1223
			statement_timeout_active = false;
			cancel_from_timeout = false;
			deadlock_timeout_active = false;
1224 1225
			return false;
		}
1226 1227
	}

1228 1229 1230 1231
	/* Always cancel deadlock timeout, in case this is error cleanup */
	deadlock_timeout_active = false;

	/* Cancel or reschedule statement timeout */
1232
	if (is_statement_timeout)
1233
	{
1234
		statement_timeout_active = false;
1235 1236
		cancel_from_timeout = false;
	}
1237 1238 1239 1240 1241
	else if (statement_timeout_active)
	{
		if (!CheckStatementTimeout())
			return false;
	}
1242 1243 1244
	return true;
}

1245

1246
/*
1247 1248 1249
 * Check for statement timeout.  If the timeout time has come,
 * trigger a query-cancel interrupt; if not, reschedule the SIGALRM
 * interrupt to occur at the right time.
1250
 *
1251
 * Returns true if okay, false if failed to set the interrupt.
1252
 */
1253 1254
static bool
CheckStatementTimeout(void)
1255
{
1256
	TimestampTz now;
B
Bruce Momjian 已提交
1257

1258 1259 1260
	if (!statement_timeout_active)
		return true;			/* do nothing if not active */

1261
	now = GetCurrentTimestamp();
1262

1263
	if (now >= statement_fin_time)
1264
	{
1265 1266
		/* Time to die */
		statement_timeout_active = false;
1267
		cancel_from_timeout = true;
1268 1269 1270 1271
#ifdef HAVE_SETSID
		/* try to signal whole process group */
		kill(-MyProcPid, SIGINT);
#endif
1272
		kill(MyProcPid, SIGINT);
1273 1274 1275 1276
	}
	else
	{
		/* Not time yet, so (re)schedule the interrupt */
1277 1278
		long		secs;
		int			usecs;
1279 1280
		struct itimerval timeval;

1281 1282
		TimestampDifference(now, statement_fin_time,
							&secs, &usecs);
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Bruce Momjian 已提交
1283

1284 1285 1286 1287 1288 1289
		/*
		 * It's possible that the difference is less than a microsecond;
		 * ensure we don't cancel, rather than set, the interrupt.
		 */
		if (secs == 0 && usecs == 0)
			usecs = 1;
1290
		MemSet(&timeval, 0, sizeof(struct itimerval));
1291 1292
		timeval.it_value.tv_sec = secs;
		timeval.it_value.tv_usec = usecs;
1293
		if (setitimer(ITIMER_REAL, &timeval, NULL))
1294 1295 1296
			return false;
	}

1297 1298
	return true;
}
1299 1300 1301


/*
1302 1303 1304 1305 1306 1307
 * Signal handler for SIGALRM
 *
 * Process deadlock check and/or statement timeout check, as needed.
 * To avoid various edge cases, we must be careful to do nothing
 * when there is nothing to be done.  We also need to be able to
 * reschedule the timer interrupt if called before end of statement.
1308 1309 1310 1311
 */
void
handle_sig_alarm(SIGNAL_ARGS)
{
1312 1313 1314
	int			save_errno = errno;

	if (deadlock_timeout_active)
1315
	{
1316
		deadlock_timeout_active = false;
1317 1318
		CheckDeadLock();
	}
1319 1320 1321 1322 1323

	if (statement_timeout_active)
		(void) CheckStatementTimeout();

	errno = save_errno;
1324
}