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On platforms without support for 64bit atomic operations where we also cannot rely on 64bit reads to have single copy atomicity, such atomics are implemented using a spinlock based fallback. That means it's not safe to even read such atomics from within a signal handler (since the signal handler might run when the spinlock already is held). To avoid this issue defer global barrier processing out of the signal handler. Instead of checking local / shared barrier generation to determine whether to set ProcSignalBarrierPending, introduce PROCSIGNAL_BARRIER and always set ProcSignalBarrierPending when receiving such a signal. Additionally avoid redundant work in ProcessProcSignalBarrier if ProcSignalBarrierPending is unnecessarily. Also do a small amount of other polishing. Author: Andres Freund Reviewed-By: Robert Haas Discussion: https://postgr.es/m/20200609193723.eu5ilsjxwdpyxhgz@alap3.anarazel.de Backpatch: 13-, where the code was introduced.
76 lines
2.4 KiB
C
76 lines
2.4 KiB
C
/*-------------------------------------------------------------------------
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*
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* procsignal.h
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* Routines for interprocess signaling
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*
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*
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* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/storage/procsignal.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PROCSIGNAL_H
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#define PROCSIGNAL_H
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#include "storage/backendid.h"
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/*
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* Reasons for signaling a Postgres child process (a backend or an auxiliary
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* process, like checkpointer). We can cope with concurrent signals for different
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* reasons. However, if the same reason is signaled multiple times in quick
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* succession, the process is likely to observe only one notification of it.
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* This is okay for the present uses.
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*
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* Also, because of race conditions, it's important that all the signals be
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* defined so that no harm is done if a process mistakenly receives one.
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*/
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typedef enum
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{
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PROCSIG_CATCHUP_INTERRUPT, /* sinval catchup interrupt */
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PROCSIG_NOTIFY_INTERRUPT, /* listen/notify interrupt */
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PROCSIG_PARALLEL_MESSAGE, /* message from cooperating parallel backend */
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PROCSIG_WALSND_INIT_STOPPING, /* ask walsenders to prepare for shutdown */
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PROCSIG_BARRIER, /* global barrier interrupt */
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/* Recovery conflict reasons */
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PROCSIG_RECOVERY_CONFLICT_DATABASE,
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PROCSIG_RECOVERY_CONFLICT_TABLESPACE,
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PROCSIG_RECOVERY_CONFLICT_LOCK,
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PROCSIG_RECOVERY_CONFLICT_SNAPSHOT,
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PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
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PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
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NUM_PROCSIGNALS /* Must be last! */
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} ProcSignalReason;
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typedef enum
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{
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/*
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* XXX. PROCSIGNAL_BARRIER_PLACEHOLDER should be replaced when the first
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* real user of the ProcSignalBarrier mechanism is added. It's just here
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* for now because we can't have an empty enum.
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*/
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PROCSIGNAL_BARRIER_PLACEHOLDER = 0
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} ProcSignalBarrierType;
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/*
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* prototypes for functions in procsignal.c
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*/
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extern Size ProcSignalShmemSize(void);
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extern void ProcSignalShmemInit(void);
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extern void ProcSignalInit(int pss_idx);
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extern int SendProcSignal(pid_t pid, ProcSignalReason reason,
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BackendId backendId);
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extern uint64 EmitProcSignalBarrier(ProcSignalBarrierType type);
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extern void WaitForProcSignalBarrier(uint64 generation);
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extern void ProcessProcSignalBarrier(void);
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extern void procsignal_sigusr1_handler(SIGNAL_ARGS);
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#endif /* PROCSIGNAL_H */
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