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Fix latent portability issue in pgwin32_dispatch_queued_signals().

The first iteration of the signal-checking loop would compute sigmask(0)which expands to 1<<(-1) which is undefined behavior according to theC standard. The lack of field reports of trouble suggest that itevaluates to 0 on all existing Windows compilers, but that's hardlysomething to rely on. Since signal 0 isn't a queueable signal anyway,we can just make the loop iterate from 1 instead, and save a few cyclesas well as avoiding the undefined behavior.In passing, avoid evaluating the volatile expression UNBLOCKED_SIGNAL_QUEUEtwice in a row; there's no reason to waste cycles like that.Noted by Aleksander Alekseev, though this isn't his proposed fix.Back-patch to all supported branches.

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src/backend/port/win32
- signal.c

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`‎src/backend/port/win32/signal.c`

Lines changed: 5 additions & 4 deletions

Original file line number	Diff line number	Diff line change
`@@ -33,6 +33,7 @@ HANDLEpgwin32_initial_signal_pipe = INVALID_HANDLE_VALUE;`
`33`	`33`	`*/`
`34`	`34`	`staticCRITICAL_SECTIONpg_signal_crit_sec;`
`35`	`35`
	`36`	`+/* Note that array elements 0 are unused since they correspond to signal 0 */`
`36`	`37`	`staticpqsigfuncpg_signal_array[PG_SIGNAL_COUNT];`
`37`	`38`	`staticpqsigfuncpg_signal_defaults[PG_SIGNAL_COUNT];`
`38`	`39`
`@@ -105,15 +106,15 @@ pgwin32_signal_initialize(void)`
`105`	`106`	`void`
`106`	`107`	`pgwin32_dispatch_queued_signals(void)`
`107`	`108`	`{`
`108`		`-inti;`
	`109`	`+intexec_mask;`
`109`	`110`
`110`	`111`	`EnterCriticalSection(&pg_signal_crit_sec);`
`111`		`-while (UNBLOCKED_SIGNAL_QUEUE())`
	`112`	`+while ((exec_mask=UNBLOCKED_SIGNAL_QUEUE())!=0)`
`112`	`113`	`{`
`113`	`114`	`/* One or more unblocked signals queued for execution */`
`114`		`-intexec_mask=UNBLOCKED_SIGNAL_QUEUE();`
	`115`	`+inti;`
`115`	`116`
`116`		`-for (i=0;i<PG_SIGNAL_COUNT;i++)`
	`117`	`+for (i=1;i<PG_SIGNAL_COUNT;i++)`
`117`	`118`	`{`
`118`	`119`	`if (exec_mask&sigmask(i))`
`119`	`120`	`{`

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Commit58666ed

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`‎src/backend/port/win32/signal.c`

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