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annotate m4/usleep.m4 @ 16869:38e6d30d7e4d

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poll/select: prevent busy-waiting 2012-05-21 Paolo Bonzini <bonzini@gnu.org> poll/select: prevent busy-waiting. SwitchToThread() only gives away the rest of the current time slice to another thread in the current process. So if the thread that feeds the file decscriptor we're polling is not in the current process, we get busy-waiting. * lib/poll.c: Use SleepEx(1, TRUE) instead of SwitchToThread(). Patch from Theodore Leblond. * lib/select.c: Split polling out of the loop that sets the output fd_sets. Check for zero result and loop if the wait timeout is infinite.
author Paolo Bonzini <bonzini@gnu.org>
date Mon, 21 May 2012 09:52:42 +0200
parents b187fc49964b
children e542fd46ad6f
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1 # usleep.m4 serial 3
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2 dnl Copyright (C) 2009-2012 Free Software Foundation, Inc.
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3 dnl This file is free software; the Free Software Foundation
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4 dnl gives unlimited permission to copy and/or distribute it,
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5 dnl with or without modifications, as long as this notice is preserved.
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6
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7 dnl This macro intentionally does not check for select or nanosleep;
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8 dnl both of those modules can require external libraries.
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9 AC_DEFUN([gl_FUNC_USLEEP],
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10 [
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11 AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
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12 dnl usleep was required in POSIX 2001, but dropped as obsolete in
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13 dnl POSIX 2008; therefore, it is not always exposed in headers.
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14 AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
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15 AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
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16 AC_CHECK_FUNCS_ONCE([usleep])
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17 AC_CHECK_TYPE([useconds_t], [],
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18 [AC_DEFINE([useconds_t], [unsigned int], [Define to an unsigned 32-bit
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19 type if <sys/types.h> lacks this type.])])
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20 if test $ac_cv_func_usleep = no; then
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21 HAVE_USLEEP=0
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22 else
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23 dnl POSIX allows implementations to reject arguments larger than
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24 dnl 999999, but GNU guarantees it will work.
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25 AC_CACHE_CHECK([whether usleep allows large arguments],
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26 [gl_cv_func_usleep_works],
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27 [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
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28 #include <unistd.h>
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29 ]], [[return !!usleep (1000000);]])],
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30 [gl_cv_func_usleep_works=yes], [gl_cv_func_usleep_works=no],
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31 [case "$host_os" in
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32 # Guess yes on glibc systems.
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33 *-gnu*) gl_cv_func_usleep_works="guessing yes" ;;
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34 # If we don't know, assume the worst.
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35 *) gl_cv_func_usleep_works="guessing no" ;;
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36 esac
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37 ])])
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38 case "$gl_cv_func_usleep_works" in
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39 *yes) ;;
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40 *)
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41 REPLACE_USLEEP=1
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42 ;;
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43 esac
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44 fi
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45 ])