pg_usleep - Mailing list pgsql-patches

Tom Lane wrote:

>Andrew Dunstan <andrew@dunslane.net> writes:
>
>
>>I wrote:
>>
>>
>>>There are a couple of other places where [select()] is used for small
>>>sleeps (storage/lmgr/s_lock.c and access/transam/xact.c) -
>>>
>>>
>
>
>
>>What is the preferred way to handle these 2 cases?  We could handle them
>>with #ifdef'd code inline, or create a new function pg_usleep(), or
>>possibly handle it with conditional macros inline. If a new function or
>>macro, where should they go?
>>
>>
>
>I'd go with a new function.  There is no reason to try to "optimize"
>this code by putting it inline; if you're trying to delay, another few
>nanoseconds to enter a subroutine doesn't matter.
>
>As for where, maybe make a new file in src/port/.  That would make it
>relatively easy to use the same function in client-side code if we
>needed to.
>
>
>
patch + new file attached. Haven't tested on Windows, but should be fine.

cheers

andrew
/*-------------------------------------------------------------------------
 *
 * pg_usleep.c
 *    platform independent version of usleep
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 *
 *  Uses select() everywhere except for Windows, where it doesn't work
 *
 * IDENTIFICATION
 *    $PostgreSQL$
 *
 *-------------------------------------------------------------------------
 */


#include "postgres.h"

#ifdef WIN32
#include <windows.h>
#else
#include <unistd.h>
#include <sys/time.h>
#endif

void
pg_usleep (unsigned int usecs)
{

#ifdef WIN32
    Sleep(usecs < 500 : 1 : (usecs+500)/ 1000);
#else
    struct timeval tv;

    tv.tv_sec = usecs / 1000000;
    tv.tv_usec = usecs % 1000000;
    select(0,NULL,NULL,NULL,&tv);

#endif

}
Index: src/Makefile.global.in
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/Makefile.global.in,v
retrieving revision 1.172
diff -c -w -r1.172 Makefile.global.in
*** src/Makefile.global.in    19 Dec 2003 23:29:15 -0000    1.172
--- src/Makefile.global.in    30 Dec 2003 18:50:56 -0000
***************
*** 342,348 ****
  #
  # substitute implementations of the C library

! LIBOBJS = @LIBOBJS@ path.o sprompt.o thread.o

  ifneq (,$(LIBOBJS))
  LIBS += -lpgport
--- 342,348 ----
  #
  # substitute implementations of the C library

! LIBOBJS = @LIBOBJS@ path.o sprompt.o thread.o pg_usleep.o

  ifneq (,$(LIBOBJS))
  LIBS += -lpgport
Index: src/backend/access/transam/xact.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/access/transam/xact.c,v
retrieving revision 1.158
diff -c -w -r1.158 xact.c
*** src/backend/access/transam/xact.c    2 Dec 2003 19:26:47 -0000    1.158
--- src/backend/access/transam/xact.c    30 Dec 2003 18:50:56 -0000
***************
*** 562,572 ****
              if (CommitDelay > 0 && enableFsync &&
                  CountActiveBackends() >= CommitSiblings)
              {
!                 struct timeval delay;
!
!                 delay.tv_sec = 0;
!                 delay.tv_usec = CommitDelay;
!                 (void) select(0, NULL, NULL, NULL, &delay);
              }

              XLogFlush(recptr);
--- 562,569 ----
              if (CommitDelay > 0 && enableFsync &&
                  CountActiveBackends() >= CommitSiblings)
              {
!                 /* call platform independent usleep */
!                 pg_usleep(CommitDelay);
              }

              XLogFlush(recptr);
Index: src/backend/storage/lmgr/s_lock.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/storage/lmgr/s_lock.c,v
retrieving revision 1.23
diff -c -w -r1.23 s_lock.c
*** src/backend/storage/lmgr/s_lock.c    27 Dec 2003 20:58:58 -0000    1.23
--- src/backend/storage/lmgr/s_lock.c    30 Dec 2003 18:50:56 -0000
***************
*** 46,52 ****
  s_lock(volatile slock_t *lock, const char *file, int line)
  {
      /*
!      * We loop tightly for awhile, then delay using select() and try
       * again. Preferably, "awhile" should be a small multiple of the
       * maximum time we expect a spinlock to be held.  100 iterations seems
       * about right.  In most multi-CPU scenarios, the spinlock is probably
--- 46,52 ----
  s_lock(volatile slock_t *lock, const char *file, int line)
  {
      /*
!      * We loop tightly for awhile, then delay using pg_usleep() and try
       * again. Preferably, "awhile" should be a small multiple of the
       * maximum time we expect a spinlock to be held.  100 iterations seems
       * about right.  In most multi-CPU scenarios, the spinlock is probably
***************
*** 84,90 ****
      int            spins = 0;
      int            delays = 0;
      int            cur_delay = MIN_DELAY_CSEC;
-     struct timeval delay;

      while (TAS(lock))
      {
--- 84,89 ----
***************
*** 97,105 ****
              if (++delays > NUM_DELAYS)
                  s_lock_stuck(lock, file, line);

!             delay.tv_sec = cur_delay / 100;
!             delay.tv_usec = (cur_delay % 100) * 10000;
!             (void) select(0, NULL, NULL, NULL, &delay);

  #if defined(S_LOCK_TEST)
              fprintf(stdout, "*");
--- 96,102 ----
              if (++delays > NUM_DELAYS)
                  s_lock_stuck(lock, file, line);

!             pg_usleep(cur_delay * 10000);

  #if defined(S_LOCK_TEST)
              fprintf(stdout, "*");
Index: src/include/port.h
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/include/port.h,v
retrieving revision 1.15
diff -c -w -r1.15 port.h
*** src/include/port.h    29 Nov 2003 22:40:53 -0000    1.15
--- src/include/port.h    30 Dec 2003 18:50:56 -0000
***************
*** 122,124 ****
--- 122,127 ----
                  char *buffer, size_t buflen,
                  struct hostent **result,
                  int *herrno);
+
+ extern void pg_usleep(unsigned int usecs);
+