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Small improvements in comments in async.c.

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We seem to have lost a line somewhere along the way in the comment block
that discusses async.c's locks, because it suddenly refers to "both locks"
without previously having mentioned more than one.  Add a sentence to make
that read more sanely.  Also, refer to the "pos of the slowest backend"
not the "tail of the slowest backend", since we have no per-backend value
called "tail".
This commit is contained in:
Tom Lane 2015-09-29 22:06:59 -04:00
parent a16db3a07d
commit 6057f61b4d
1 changed files with 2 additions and 1 deletions
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src/backend/commands/async.c
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@ -224,6 +224,7 @@ typedef struct QueueBackendStatus
* When holding the lock in EXCLUSIVE mode, backends can inspect the entries * When holding the lock in EXCLUSIVE mode, backends can inspect the entries
* of other backends and also change the head and tail pointers. * of other backends and also change the head and tail pointers.
* *
* AsyncCtlLock is used as the control lock for the pg_notify SLRU buffers.
* In order to avoid deadlocks, whenever we need both locks, we always first * In order to avoid deadlocks, whenever we need both locks, we always first
* get AsyncQueueLock and then AsyncCtlLock. * get AsyncQueueLock and then AsyncCtlLock.
* *
@ -234,7 +235,7 @@ typedef struct QueueBackendStatus
typedef struct AsyncQueueControl typedef struct AsyncQueueControl
{ {
QueuePosition head; /* head points to the next free location */ QueuePosition head; /* head points to the next free location */
QueuePosition tail; /* the global tail is equivalent to the tail QueuePosition tail; /* the global tail is equivalent to the pos
* of the "slowest" backend */ * of the "slowest" backend */
TimestampTz lastQueueFillWarn; /* time of last queue-full msg */ TimestampTz lastQueueFillWarn; /* time of last queue-full msg */
QueueBackendStatus backend[FLEXIBLE_ARRAY_MEMBER]; QueueBackendStatus backend[FLEXIBLE_ARRAY_MEMBER];