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ccf312a448
In the wake of commit aced5a92b, the semantics of these results are a bit squishy: we can tell whether we signaled some other process(es), but we do not know which ones were real waiters versus mere sentinels for ConditionVariableBroadcast operations. It does not help much that ConditionVariableBroadcast will attempt to pass on the signal to the next real waiter, because (a) there might not be one, and (b) that will only happen awhile later, anyway. So these results could overstate how much effect the calls really had. However, no existing caller of either function pays any attention to its result value, so it seems reasonable to just define that as a required property of a correct algorithm. To encourage correctness and save some tiny number of cycles, change both functions to return void. Patch by me, per an observation by Thomas Munro. No back-patch, since if any third parties happen to be using these functions, they might not appreciate an API break in a minor release. Discussion: https://postgr.es/m/CAEepm=0NWKehYw7NDoUSf8juuKOPRnCyY3vuaSvhrEWsOTAa3w@mail.gmail.com
60 lines
2.3 KiB
C
60 lines
2.3 KiB
C
/*-------------------------------------------------------------------------
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*
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* condition_variable.h
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* Condition variables
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*
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* A condition variable is a method of waiting until a certain condition
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* becomes true. Conventionally, a condition variable supports three
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* operations: (1) sleep; (2) signal, which wakes up one process sleeping
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* on the condition variable; and (3) broadcast, which wakes up every
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* process sleeping on the condition variable. In our implementation,
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* condition variables put a process into an interruptible sleep (so it
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* can be cancelled prior to the fulfillment of the condition) and do not
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* use pointers internally (so that they are safe to use within DSMs).
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*
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* Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/storage/condition_variable.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef CONDITION_VARIABLE_H
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#define CONDITION_VARIABLE_H
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#include "storage/s_lock.h"
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#include "storage/proclist_types.h"
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typedef struct
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{
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slock_t mutex;
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proclist_head wakeup;
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} ConditionVariable;
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/* Initialize a condition variable. */
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extern void ConditionVariableInit(ConditionVariable *);
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/*
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* To sleep on a condition variable, a process should use a loop which first
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* checks the condition, exiting the loop if it is met, and then calls
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* ConditionVariableSleep. Spurious wakeups are possible, but should be
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* infrequent. After exiting the loop, ConditionVariableCancelSleep should
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* be called to ensure that the process is no longer in the wait list for
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* the condition variable.
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*/
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extern void ConditionVariableSleep(ConditionVariable *, uint32 wait_event_info);
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extern void ConditionVariableCancelSleep(void);
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/*
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* The use of this function is optional and not necessary for correctness;
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* for efficiency, it should be called prior entering the loop described above
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* if it is thought that the condition is unlikely to hold immediately.
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*/
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extern void ConditionVariablePrepareToSleep(ConditionVariable *);
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/* Wake up a single waiter (via signal) or all waiters (via broadcast). */
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extern void ConditionVariableSignal(ConditionVariable *cv);
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extern void ConditionVariableBroadcast(ConditionVariable *cv);
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#endif /* CONDITION_VARIABLE_H */
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