src/port/pgsleep.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * pgsleep.c
   4  *         Portable delay handling.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
   8  *
   9  * src/port/pgsleep.c
  10  *
  11  *-------------------------------------------------------------------------
  12  */
  13 #include "c.h"
  14
  15 #include <unistd.h>
  16 #include <sys/select.h>
  17 #include <sys/time.h>
  18
  19 /*
  20  * In a Windows backend, we don't use this implementation, but rather
  21  * the signal-aware version in src/backend/port/win32/signal.c.
  22  */
  23 #if defined(FRONTEND) || !defined(WIN32)
  24
  25 /*
  26  * pg_usleep --- delay the specified number of microseconds.
  27  *
  28  * NOTE: although the delay is specified in microseconds, the effective
  29  * resolution is only 1/HZ, or 10 milliseconds, on most Unixen.  Expect
  30  * the requested delay to be rounded up to the next resolution boundary.
  31  *
  32  * On machines where "long" is 32 bits, the maximum delay is ~2000 seconds.
  33  *
  34  * CAUTION: the behavior when a signal arrives during the sleep is platform
  35  * dependent.  On most Unix-ish platforms, a signal does not terminate the
  36  * sleep; but on some, it will (the Windows implementation also allows signals
  37  * to terminate pg_usleep).  And there are platforms where not only does a
  38  * signal not terminate the sleep, but it actually resets the timeout counter
  39  * so that the sleep effectively starts over!  It is therefore rather hazardous
  40  * to use this for long sleeps; a continuing stream of signal events could
  41  * prevent the sleep from ever terminating.  Better practice for long sleeps
  42  * is to use WaitLatch() with a timeout.
  43  */
  44 void
  45 pg_usleep(long microsec)
  46 {
  47         if (microsec > 0)
  48         {
  49 #ifndef WIN32
  50                 struct timeval delay;
  51
  52                 delay.tv_sec = microsec / 1000000L;
  53                 delay.tv_usec = microsec % 1000000L;
  54                 (void) select(0, NULL, NULL, NULL, &delay);
  55 #else
  56                 SleepEx((microsec < 500 ? 1 : (microsec + 500) / 1000), FALSE);
  57 #endif
  58         }
  59 }
  60
  61 #endif                                                  /* defined(FRONTEND) || !defined(WIN32) */