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a948e49e2e
The previous coding based on select() had commentary about historical portability concerns. Use POSIX nanosleep() instead. This has independently been suggested a couple of times before, but never managed to stick. Since recent and proposed work removes other uses of select(), and associated code and comments relating to its non-portable interaction with signals, it seems like a good time to tidy up this case, too. Also modernize the explanation of why WaitLatch() is a better way to wait. Reviewed-by: Nathan Bossart <nathandbossart@gmail.com> Suggested-by: Paul Guo <paulguo@gmail.com> Suggested-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/CAAKRu_b-q0hXCBUCAATh0Z4Zi6UkiC0k2DFgoD3nC-r3SkR3tg%40mail.gmail.com Discussion: https://postgr.es/m/CABQrizfxpBLZT5mZeE0js5oCh1tqEWvcGF3vMRCv5P-RwUY5dQ@mail.gmail.com Discussion: https://postgr.es/m/4902.1552349020@sss.pgh.pa.us
58 lines
1.7 KiB
C
58 lines
1.7 KiB
C
/*-------------------------------------------------------------------------
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*
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* pgsleep.c
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* Portable delay handling.
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*
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*
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* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
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*
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* src/port/pgsleep.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "c.h"
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#include <time.h>
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/*
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* In a Windows backend, we don't use this implementation, but rather
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* the signal-aware version in src/backend/port/win32/signal.c.
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*/
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#if defined(FRONTEND) || !defined(WIN32)
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/*
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* pg_usleep --- delay the specified number of microseconds.
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*
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* NOTE: Although the delay is specified in microseconds, older Unixen and
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* Windows use periodic kernel ticks to wake up, which might increase the delay
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* time significantly. We've observed delay increases as large as 20
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* milliseconds on supported platforms.
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*
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* On machines where "long" is 32 bits, the maximum delay is ~2000 seconds.
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*
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* CAUTION: It's not a good idea to use long sleeps in the backend. They will
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* silently return early if a signal is caught, but that doesn't include
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* latches being set on most OSes, and even signal handlers that set MyLatch
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* might happen to run before the sleep begins, allowing the full delay.
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* Better practice is to use WaitLatch() with a timeout, so that backends
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* respond to latches and signals promptly.
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*/
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void
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pg_usleep(long microsec)
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{
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if (microsec > 0)
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{
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#ifndef WIN32
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struct timespec delay;
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delay.tv_sec = microsec / 1000000L;
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delay.tv_nsec = (microsec % 1000000L) * 1000;
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(void) nanosleep(&delay, NULL);
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#else
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SleepEx((microsec < 500 ? 1 : (microsec + 500) / 1000), FALSE);
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#endif
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}
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}
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#endif /* defined(FRONTEND) || !defined(WIN32) */
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