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/*-------------------------------------------------------------------------
*
* condition_variable.h
* Condition variables
*
* A condition variable is a method of waiting until a certain condition
* becomes true. Conventionally, a condition variable supports three
* operations: (1) sleep; (2) signal, which wakes up one process sleeping
* on the condition variable; and (3) broadcast, which wakes up every
* process sleeping on the condition variable. In our implementation,
* condition variables put a process into an interruptible sleep (so it
* can be canceled prior to the fulfillment of the condition) and do not
* use pointers internally (so that they are safe to use within DSMs).
*
* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/condition_variable.h
*
*-------------------------------------------------------------------------
*/
#ifndef CONDITION_VARIABLE_H
#define CONDITION_VARIABLE_H
#include "storage/proclist_types.h"
#include "storage/spin.h"
typedef struct
{
slock_t mutex; /* spinlock protecting the wakeup list */
proclist_head wakeup; /* list of wake-able processes */
} ConditionVariable;
/*
* Pad a condition variable to a power-of-two size so that an array of
* condition variables does not cross a cache line boundary.
*/
#define CV_MINIMAL_SIZE (sizeof(ConditionVariable) <= 16 ? 16 : 32)
typedef union ConditionVariableMinimallyPadded
{
ConditionVariable cv;
char pad[CV_MINIMAL_SIZE];
} ConditionVariableMinimallyPadded;
/* Initialize a condition variable. */
extern void ConditionVariableInit(ConditionVariable *cv);
/*
* To sleep on a condition variable, a process should use a loop which first
* checks the condition, exiting the loop if it is met, and then calls
* ConditionVariableSleep. Spurious wakeups are possible, but should be
* infrequent. After exiting the loop, ConditionVariableCancelSleep must
* be called to ensure that the process is no longer in the wait list for
* the condition variable.
*/
extern void ConditionVariableSleep(ConditionVariable *cv, uint32 wait_event_info);
extern bool ConditionVariableTimedSleep(ConditionVariable *cv, long timeout,
uint32 wait_event_info);
extern void ConditionVariableCancelSleep(void);
/*
* Optionally, ConditionVariablePrepareToSleep can be called before entering
* the test-and-sleep loop described above. Doing so is more efficient if
* at least one sleep is needed, whereas not doing so is more efficient when
* no sleep is needed because the test condition is true the first time.
*/
extern void ConditionVariablePrepareToSleep(ConditionVariable *cv);
/* Wake up a single waiter (via signal) or all waiters (via broadcast). */
extern void ConditionVariableSignal(ConditionVariable *cv);
extern void ConditionVariableBroadcast(ConditionVariable *cv);
#endif /* CONDITION_VARIABLE_H */
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