condition_variable.c File Reference

#include "postgres.h"
#include "miscadmin.h"
#include "storage/condition_variable.h"
#include "storage/ipc.h"
#include "storage/proc.h"
#include "storage/proclist.h"
#include "storage/spin.h"
#include "utils/memutils.h"

Include dependency graph for condition_variable.c:

Go to the source code of this file.

Functions
void	ConditionVariableInit (ConditionVariable *cv)
void	ConditionVariablePrepareToSleep (ConditionVariable *cv)
void	ConditionVariableSleep (ConditionVariable *cv, uint32 wait_event_info)
void	ConditionVariableCancelSleep (void)
bool	ConditionVariableSignal (ConditionVariable *cv)
int	ConditionVariableBroadcast (ConditionVariable *cv)

Variables
static ConditionVariable *	cv_sleep_target = NULL
static WaitEventSet *	cv_wait_event_set = NULL

Function Documentation

int ConditionVariableBroadcast

(

ConditionVariable *

cv

)

Definition at line 214 of file condition_variable.c.

References ConditionVariableSignal().

Referenced by _bt_parallel_done(), and BitmapDoneInitializingSharedState().

{
    int         nwoken = 0;

    /*
     * Let's just do this the dumbest way possible.  We could try to dequeue
     * all the sleepers at once to save spinlock cycles, but it's a bit hard
     * to get that right in the face of possible sleep cancelations, and we
     * don't want to loop holding the mutex.
     */
    while (ConditionVariableSignal(cv))
        ++nwoken;

    return nwoken;
}

void ConditionVariableCancelSleep

(

void

)

Definition at line 166 of file condition_variable.c.

References cv_sleep_target, ConditionVariable::mutex, MyProc, NULL, PGPROC::pgprocno, proclist_contains, proclist_delete, SpinLockAcquire, SpinLockRelease, and ConditionVariable::wakeup.

Referenced by _bt_parallel_seize(), AbortTransaction(), AuxiliaryProcKill(), BackgroundWriterMain(), BitmapShouldInitializeSharedState(), CheckpointerMain(), ProcKill(), ShutdownAuxiliaryProcess(), WalSndErrorCleanup(), and WalWriterMain().

{
    ConditionVariable *cv = cv_sleep_target;

    if (cv == NULL)
        return;

    SpinLockAcquire(&cv->mutex);
    if (proclist_contains(&cv->wakeup, MyProc->pgprocno, cvWaitLink))
        proclist_delete(&cv->wakeup, MyProc->pgprocno, cvWaitLink);
    SpinLockRelease(&cv->mutex);

    cv_sleep_target = NULL;
}

void ConditionVariableInit

(

ConditionVariable *

cv

)

Definition at line 39 of file condition_variable.c.

References ConditionVariable::mutex, proclist_init(), SpinLockInit, and ConditionVariable::wakeup.

Referenced by btinitparallelscan(), and ExecBitmapHeapInitializeDSM().

{
    SpinLockInit(&cv->mutex);
    proclist_init(&cv->wakeup);
}

void ConditionVariablePrepareToSleep

(

ConditionVariable *

cv

)

Definition at line 53 of file condition_variable.c.

References AddWaitEventToSet(), Assert, CreateWaitEventSet(), ConditionVariable::mutex, MyProc, NULL, PGINVALID_SOCKET, PGPROC::pgprocno, PGPROC::procLatch, proclist_contains, proclist_push_tail, ResetLatch(), SpinLockAcquire, SpinLockRelease, TopMemoryContext, ConditionVariable::wakeup, and WL_LATCH_SET.

Referenced by ConditionVariableSleep().

{
    int         pgprocno = MyProc->pgprocno;

    /*
     * It's not legal to prepare a sleep until the previous sleep has been
     * completed or canceled.
     */
    Assert(cv_sleep_target == NULL);

    /* Record the condition variable on which we will sleep. */
    cv_sleep_target = cv;

    /* Create a reusable WaitEventSet. */
    if (cv_wait_event_set == NULL)
    {
        cv_wait_event_set = CreateWaitEventSet(TopMemoryContext, 1);
        AddWaitEventToSet(cv_wait_event_set, WL_LATCH_SET, PGINVALID_SOCKET,
                          &MyProc->procLatch, NULL);
    }

    /*
     * Reset my latch before adding myself to the queue and before entering
     * the caller's predicate loop.
     */
    ResetLatch(&MyProc->procLatch);

    /* Add myself to the wait queue. */
    SpinLockAcquire(&cv->mutex);
    if (!proclist_contains(&cv->wakeup, pgprocno, cvWaitLink))
        proclist_push_tail(&cv->wakeup, pgprocno, cvWaitLink);
    SpinLockRelease(&cv->mutex);
}

bool ConditionVariableSignal

(

ConditionVariable *

cv

)

Definition at line 187 of file condition_variable.c.

References ConditionVariable::mutex, NULL, PGPROC::procLatch, proclist_is_empty(), proclist_pop_head_node, SetLatch(), SpinLockAcquire, SpinLockRelease, and ConditionVariable::wakeup.

Referenced by _bt_parallel_release(), and ConditionVariableBroadcast().

{
    PGPROC     *proc = NULL;

    /* Remove the first process from the wakeup queue (if any). */
    SpinLockAcquire(&cv->mutex);
    if (!proclist_is_empty(&cv->wakeup))
        proc = proclist_pop_head_node(&cv->wakeup, cvWaitLink);
    SpinLockRelease(&cv->mutex);

    /* If we found someone sleeping, set their latch to wake them up. */
    if (proc != NULL)
    {
        SetLatch(&proc->procLatch);
        return true;
    }

    /* No sleeping processes. */
    return false;
}

void ConditionVariableSleep	(	ConditionVariable *	cv,
		uint32	wait_event_info
	)

Definition at line 102 of file condition_variable.c.

References Assert, CHECK_FOR_INTERRUPTS, ConditionVariablePrepareToSleep(), ConditionVariable::mutex, MyProc, NULL, PGPROC::pgprocno, PGPROC::procLatch, proclist_contains, proclist_push_tail, ResetLatch(), SpinLockAcquire, SpinLockRelease, WaitEventSetWait(), and ConditionVariable::wakeup.

Referenced by _bt_parallel_seize(), and BitmapShouldInitializeSharedState().

{
    WaitEvent   event;
    bool        done = false;

    /*
     * If the caller didn't prepare to sleep explicitly, then do so now and
     * return immediately.  The caller's predicate loop should immediately
     * call again if its exit condition is not yet met.  This initial spurious
     * return can be avoided by calling ConditionVariablePrepareToSleep(cv)
     * first.  Whether it's worth doing that depends on whether you expect the
     * condition to be met initially, in which case skipping the prepare
     * allows you to skip manipulation of the wait list, or not met initially,
     * in which case preparing first allows you to skip a spurious test of the
     * caller's exit condition.
     */
    if (cv_sleep_target == NULL)
    {
        ConditionVariablePrepareToSleep(cv);
        return;
    }

    /* Any earlier condition variable sleep must have been canceled. */
    Assert(cv_sleep_target == cv);

    while (!done)
    {
        CHECK_FOR_INTERRUPTS();

        /*
         * Wait for latch to be set.  We don't care about the result because
         * our contract permits spurious returns.
         */
        WaitEventSetWait(cv_wait_event_set, -1, &event, 1, wait_event_info);

        /* Reset latch before testing whether we can return. */
        ResetLatch(&MyProc->procLatch);

        /*
         * If this process has been taken out of the wait list, then we know
         * that is has been signaled by ConditionVariableSignal.  We put it
         * back into the wait list, so we don't miss any further signals while
         * the caller's loop checks its condition.  If it hasn't been taken
         * out of the wait list, then the latch must have been set by
         * something other than ConditionVariableSignal; though we don't
         * guarantee not to return spuriously, we'll avoid these obvious
         * cases.
         */
        SpinLockAcquire(&cv->mutex);
        if (!proclist_contains(&cv->wakeup, MyProc->pgprocno, cvWaitLink))
        {
            done = true;
            proclist_push_tail(&cv->wakeup, MyProc->pgprocno, cvWaitLink);
        }
        SpinLockRelease(&cv->mutex);
    }
}

Variable Documentation

ConditionVariable* cv_sleep_target = NULL

static

Definition at line 30 of file condition_variable.c.

Referenced by ConditionVariableCancelSleep().

WaitEventSet* cv_wait_event_set = NULL

static

Definition at line 33 of file condition_variable.c.