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Make critical sections (elog->crash) and interrupt holdoff sections

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into distinct concepts, per recent discussion on pghackers.
This commit is contained in:
Tom Lane
2001-01-19 22:08:47 +00:00
parent 75815c3100
commit 6ce0ed2813
9 changed files with 104 additions and 72 deletions
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33
src/include/miscadmin.h
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@ -12,7 +12,7 @@
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: miscadmin.h,v 1.77 2001/01/14 05:08:16 tgl Exp $
* $Id: miscadmin.h,v 1.78 2001/01/19 22:08:47 tgl Exp $
*
* NOTES
* some of the information in this file should be moved to
@ -26,7 +26,7 @@
#include "storage/ipc.h"
/*****************************************************************************
* System interrupt handling
* System interrupt and critical section handling
*
* There are two types of interrupts that a running backend needs to accept
* without messing up its state: QueryCancel (SIGINT) and ProcDie (SIGTERM).
@ -40,15 +40,23 @@
* where it is normally safe to accept a cancel or die interrupt. In some
* cases, we invoke CHECK_FOR_INTERRUPTS() inside low-level subroutines that
* might sometimes be called in contexts that do *not* want to allow a cancel
* or die interrupt. The CRIT_SECTION mechanism allows code to ensure that
* no cancel or die interrupt will be accepted, even if CHECK_FOR_INTERRUPTS
* gets called in a subroutine.
* or die interrupt. The HOLD_INTERRUPTS() and RESUME_INTERRUPTS() macros
* allow code to ensure that no cancel or die interrupt will be accepted,
* even if CHECK_FOR_INTERRUPTS() gets called in a subroutine. The interrupt
* will be held off until the last matching RESUME_INTERRUPTS() occurs.
*
* Special mechanisms are used to let an interrupt be accepted when we are
* waiting for a lock or spinlock, and when we are waiting for command input
* (but, of course, only if the critical section counter is zero). See the
* (but, of course, only if the interrupt holdoff counter is zero). See the
* related code for details.
*
* A related, but conceptually distinct, mechanism is the "critical section"
* mechanism. A critical section not only holds off cancel/die interrupts,
* but causes any elog(ERROR) or elog(FATAL) to become elog(STOP) --- that is,
* a system-wide reset is forced. Needless to say, only really *critical*
* code should be marked as a critical section! Currently, this mechanism
* is only used for XLOG-related code.
*
*****************************************************************************/
/* in globals.c */
@ -58,6 +66,7 @@ extern volatile bool QueryCancelPending;
extern volatile bool ProcDiePending;
/* these are marked volatile because they are examined by signal handlers: */
extern volatile bool ImmediateInterruptOK;
extern volatile uint32 InterruptHoldoffCount;
extern volatile uint32 CritSectionCount;
/* in postgres.c */
@ -69,13 +78,23 @@ extern void ProcessInterrupts(void);
ProcessInterrupts(); \
} while(0)
#define HOLD_INTERRUPTS() (InterruptHoldoffCount++)
#define RESUME_INTERRUPTS() \
do { \
Assert(InterruptHoldoffCount > 0); \
InterruptHoldoffCount--; \
if (InterruptPending) \
ProcessInterrupts(); \
} while(0)
#define START_CRIT_SECTION() (CritSectionCount++)
#define END_CRIT_SECTION() \
do { \
Assert(CritSectionCount > 0); \
CritSectionCount--; \
if (CritSectionCount == 0 && InterruptPending) \
if (InterruptPending) \
ProcessInterrupts(); \
} while(0)