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4f85fde8eb
Up to now large swathes of backend code ran inside signal handlers while reading commands from the client, to allow for speedy reaction to asynchronous events. Most prominently shared invalidation and NOTIFY handling. That means that complex code like the starting/stopping of transactions is run in signal handlers... The required code was fragile and verbose, and is likely to contain bugs. That approach also severely limited what could be done while communicating with the client. As the read might be from within openssl it wasn't safely possible to trigger an error, e.g. to cancel a backend in idle-in-transaction state. We did that in some cases, namely fatal errors, nonetheless. Now that FE/BE communication in the backend employs non-blocking sockets and latches to block, we can quite simply interrupt reads from signal handlers by setting the latch. That allows us to signal an interrupted read, which is supposed to be retried after returning from within the ssl library. As signal handlers now only need to set the latch to guarantee timely interrupt processing, remove a fair amount of complicated & fragile code from async.c and sinval.c. We could now actually start to process some kinds of interrupts, like sinval ones, more often that before, but that seems better done separately. This work will hopefully allow to handle cases like being blocked by sending data, interrupting idle transactions and similar to be implemented without too much effort. In addition to allowing getting rid of ImmediateInterruptOK, that is. Author: Andres Freund Reviewed-By: Heikki Linnakangas
57 lines
1.6 KiB
C
57 lines
1.6 KiB
C
/*-------------------------------------------------------------------------
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*
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* async.h
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* Asynchronous notification: NOTIFY, LISTEN, UNLISTEN
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*
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* Portions Copyright (c) 1996-2015, 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/commands/async.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef ASYNC_H
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#define ASYNC_H
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#include <signal.h>
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#include "fmgr.h"
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/*
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* The number of SLRU page buffers we use for the notification queue.
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*/
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#define NUM_ASYNC_BUFFERS 8
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extern bool Trace_notify;
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extern volatile sig_atomic_t notifyInterruptPending;
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extern Size AsyncShmemSize(void);
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extern void AsyncShmemInit(void);
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/* notify-related SQL statements */
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extern void Async_Notify(const char *channel, const char *payload);
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extern void Async_Listen(const char *channel);
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extern void Async_Unlisten(const char *channel);
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extern void Async_UnlistenAll(void);
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/* notify-related SQL functions */
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extern Datum pg_listening_channels(PG_FUNCTION_ARGS);
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extern Datum pg_notify(PG_FUNCTION_ARGS);
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/* perform (or cancel) outbound notify processing at transaction commit */
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extern void PreCommit_Notify(void);
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extern void AtCommit_Notify(void);
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extern void AtAbort_Notify(void);
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extern void AtSubStart_Notify(void);
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extern void AtSubCommit_Notify(void);
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extern void AtSubAbort_Notify(void);
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extern void AtPrepare_Notify(void);
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extern void ProcessCompletedNotifies(void);
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/* signal handler for inbound notifies (PROCSIG_NOTIFY_INTERRUPT) */
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extern void HandleNotifyInterrupt(void);
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/* process interrupts */
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extern void ProcessNotifyInterrupt(void);
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#endif /* ASYNC_H */
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