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Cosmetic improvements in condition_variable.[hc].

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Clarify a bunch of comments.

Discussion: https://postgr.es/m/CAEepm=0NWKehYw7NDoUSf8juuKOPRnCyY3vuaSvhrEWsOTAa3w@mail.gmail.com
This commit is contained in:
Tom Lane
2018-01-08 18:28:03 -05:00
parent ea8e1bbc53
commit e35dba475a
2 changed files with 70 additions and 45 deletions
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23
src/include/storage/condition_variable.h
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@@ -27,30 +27,33 @@
typedef struct
{
slock_t mutex;
proclist_head wakeup;
slock_t mutex; /* spinlock protecting the wakeup list */
proclist_head wakeup; /* list of wake-able processes */
} ConditionVariable;
/* Initialize a condition variable. */
extern void ConditionVariableInit(ConditionVariable *);
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 should
* 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.
* the condition variable. Only one condition variable can be used at a
* time, ie, ConditionVariableCancelSleep must be called before any attempt
* is made to sleep on a different condition variable.
*/
extern void ConditionVariableSleep(ConditionVariable *, uint32 wait_event_info);
extern void ConditionVariableSleep(ConditionVariable *cv, uint32 wait_event_info);
extern void ConditionVariableCancelSleep(void);
/*
* The use of this function is optional and not necessary for correctness;
* for efficiency, it should be called prior entering the loop described above
* if it is thought that the condition is unlikely to hold immediately.
* 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 *);
extern void ConditionVariablePrepareToSleep(ConditionVariable *cv);
/* Wake up a single waiter (via signal) or all waiters (via broadcast). */
extern void ConditionVariableSignal(ConditionVariable *cv);