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Refactor CHECK_FOR_INTERRUPTS() to add flexibility.

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Split up CHECK_FOR_INTERRUPTS() to provide an additional macro
INTERRUPTS_PENDING_CONDITION(), which just tests whether an
interrupt is pending without attempting to service it.  This is
useful in situations where the caller knows that interrupts are
blocked, and would like to find out if it's worth the trouble
to unblock them.

Also add INTERRUPTS_CAN_BE_PROCESSED(), which indicates whether
CHECK_FOR_INTERRUPTS() can be relied on to clear the pending interrupt.

This commit doesn't actually add any uses of the new macros,
but a follow-on bug fix will do so.  Back-patch to all supported
branches to provide infrastructure for that fix.

Alvaro Herrera and Tom Lane

Discussion: https://postgr.es/m/20210513155351.GA7848@alvherre.pgsql
This commit is contained in:
Tom Lane
2021-05-14 12:54:26 -04:00
parent 1b5617eb84
commit e47f93f981
2 changed files with 35 additions and 13 deletions
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14
src/backend/tcop/postgres.c
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@ -554,7 +554,7 @@ ProcessClientWriteInterrupt(bool blocked)
{
/*
* Don't mess with whereToSendOutput if ProcessInterrupts wouldn't
* do anything.
* service ProcDiePending.
*/
if (InterruptHoldoffCount == 0 && CritSectionCount == 0)
{
@ -3118,6 +3118,12 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
* If an interrupt condition is pending, and it's safe to service it,
* then clear the flag and accept the interrupt. Called only when
* InterruptPending is true.
*
* Note: if INTERRUPTS_CAN_BE_PROCESSED() is true, then ProcessInterrupts
* is guaranteed to clear the InterruptPending flag before returning.
* (This is not the same as guaranteeing that it's still clear when we
* return; another interrupt could have arrived. But we promise that
* any pre-existing one will have been serviced.)
*/
void
ProcessInterrupts(void)
@ -3248,7 +3254,11 @@ ProcessInterrupts(void)
{
/*
* Re-arm InterruptPending so that we process the cancel request as
* soon as we're done reading the message.
* soon as we're done reading the message. (XXX this is seriously
* ugly: it complicates INTERRUPTS_CAN_BE_PROCESSED(), and it means we
* can't use that macro directly as the initial test in this function,
* meaning that this code also creates opportunities for other bugs to
* appear.)
*/
InterruptPending = true;
}