view build-scripts/mkinstalldirs @ 4105:84882a89ca50 SDL-1.2

Date: Thu, 27 Dec 2007 07:38:25 +0000 From: John Bartholomew Subject: [SDL] SDL Semaphore implementation broken on Windows? Hi, Over the past couple of days, I've been battling with SDL, SDL_Mixer and SMPEG to try to find an audio hang bug. I believe I've found the problem, which I think is a race condition inside SDL's semaphore implementation (at least the Windows implementation). The semaphore code uses Windows' built in semaphore functions, but it also maintains a separate count value. This count value is updated with bare increment and decrement operations in SemPost and SemWaitTimeout - no locking primitives to protect them. In tracking down the apparent audio bug, I found that at some point a semaphore's count value was being decremented to -1, which is clearly not a valid value for it to take. I'm still not certain exactly what sequence of operations is occuring for this to happen, but I believe that overall it's a race condition between a thread calling SemPost (which increments the count) and the thread on the other end calling SemWait (which decrements it). I will try to make a test case to verify this, but I'm not sure if I'll be able to (threading errors being difficult to reproduce even in the best circumstances). However, assuming this is the cause of my problems, there is a very simple fix: Windows provides InterlockedIncrement() and InterlockedDecrement() functions to perform increments and decrements which are guaranteed to be atomic. So the fix is in thread/win32/SDL_syssem.c: replace occurrences of --sem->count with InterlockedDecrement(&sem->count); and replace occurrences of ++sem->count with InterlockedIncrement(&sem->count); This is using SDL v1.2.12, built with VC++ 2008 Express, running on a Core 2 duo processor.
author Sam Lantinga <slouken@libsdl.org>
date Fri, 28 Dec 2007 22:05:17 +0000
parents 19418e4422cb
children
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#! /bin/sh
# mkinstalldirs --- make directory hierarchy
# Author: Noah Friedman <friedman@prep.ai.mit.edu>
# Created: 1993-05-16
# Public domain

errstatus=0
dirmode=""

usage="\
Usage: mkinstalldirs [-h] [--help] [-m mode] dir ..."

# process command line arguments
while test $# -gt 0 ; do
   case "${1}" in
     -h | --help | --h* )			# -h for help
	echo "${usage}" 1>&2; exit 0 ;;
     -m )					# -m PERM arg
	shift
	test $# -eq 0 && { echo "${usage}" 1>&2; exit 1; }
	dirmode="${1}"
	shift ;;
     -- ) shift; break ;;			# stop option processing
     -* ) echo "${usage}" 1>&2; exit 1 ;;	# unknown option
     * )  break ;;				# first non-opt arg
   esac
done

for file
do
  if test -d "$file"; then
    shift
  else
    break
  fi
done

case $# in
0) exit 0 ;;
esac

case $dirmode in
'')
  if mkdir -p -- . 2>/dev/null; then
    echo "mkdir -p -- $*"
    exec mkdir -p -- "$@"
  fi ;;
*)
  if mkdir -m "$dirmode" -p -- . 2>/dev/null; then
    echo "mkdir -m $dirmode -p -- $*"
    exec mkdir -m "$dirmode" -p -- "$@"
  fi ;;
esac

for file
do
   set fnord `echo ":$file" | sed -ne 's/^:\//#/;s/^://;s/\// /g;s/^#/\//;p'`
   shift

   pathcomp=
   for d
   do
     pathcomp="$pathcomp$d"
     case "$pathcomp" in
       -* ) pathcomp=./$pathcomp ;;
     esac

     if test ! -d "$pathcomp"; then
	echo "mkdir $pathcomp"

	mkdir "$pathcomp" || lasterr=$?

	if test ! -d "$pathcomp"; then
	  errstatus=$lasterr
	else
	  if test ! -z "$dirmode"; then
	     echo "chmod $dirmode $pathcomp"

	     lasterr=""
	     chmod "$dirmode" "$pathcomp" || lasterr=$?

	     if test ! -z "$lasterr"; then
	       errstatus=$lasterr
	     fi
	  fi
	fi
     fi

     pathcomp="$pathcomp/"
   done
done

exit $errstatus

# Local Variables:
# mode: shell-script
# sh-indentation: 3
# End:
# mkinstalldirs ends here