Mercurial > sdl-ios-xcode
view Xcode/package @ 3069:caefe2344f65
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 | Tue, 17 Feb 2009 05:39:18 +0000 |
parents | d63e9f5944ae |
children |
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#! /bin/csh -ef set prog = `/usr/bin/basename $0` set usage = "Usage: $prog [-f] root-dir info-file [tiff-file] [-d dest-dir] [-r resource-dir] [-traditional | -gnutar]" set noglob if (-x /usr/bin/mkbom) then set mkbom=/usr/bin/mkbom set lsbom=/usr/bin/lsbom else set mkbom=/usr/etc/mkbom set lsbom=/usr/etc/lsbom endif if (-x /usr/bin/awk) then set awk=/usr/bin/awk else set awk=/bin/awk endif set gnutar=/usr/bin/gnutar set tar=/usr/bin/tar set pax=/bin/pax # gather parameters if ($#argv == 0) then echo $usage exit(1) endif while ( $#argv > 0 ) switch ( $argv[1] ) case -d: if ( $?destDir ) then echo ${prog}: dest-dir parameter already set to ${destDir}. echo $usage exit(1) else if ( $#argv < 2 ) then echo ${prog}: -d option requires destination directory. echo $usage exit(1) else set destDir = $argv[2] shift; shift breaksw endif case -f: if ( $?rootDir ) then echo ${prog}: root-dir parameter already set to ${rootDir}. echo $usage exit(1) else if ( $#argv < 2 ) then echo ${prog}: -f option requires package root directory. echo $usage exit(1) else set rootDir = $argv[2] set fflag shift; shift breaksw endif case -r: if ( $?resDir ) then echo ${prog}: resource-dir parameter already set to ${resDir}. echo $usage exit(1) else if ( $#argv < 2 ) then echo ${prog}: -r option requires package resource directory. echo $usage exit(1) else set resDir = $argv[2] shift; shift breaksw endif case -traditional: set usetar unset usegnutar unset usepax breaksw case -gnutar: set usegnutar unset usepax unset usetar case -B: # We got long file names, better use bigtar instead #set archiver = /NextAdmin/Installer.app/Resources/installer_bigtar echo 2>&1 ${prog}: -B flag is no longer relevant. shift breaksw case -*: echo ${prog}: Unknown option: $argv[1] echo $usage exit(1) case *.info: if ( $?info ) then echo ${prog}: info-file parameter already set to ${info}. echo $usage exit(1) else set info = "$argv[1]" shift breaksw endif case *.tiff: if ( $?tiff ) then echo ${prog}: tiff-file parameter already set to ${tiff}. echo $usage exit(1) else set tiff = "$argv[1]" shift breaksw endif default: if ( $?rootDir ) then echo ${prog}: unrecognized parameter: $argv[1] echo $usage exit(1) else set rootDir = "$argv[1]" shift breaksw endif endsw end # check for mandatory parameters if ( ! $?rootDir ) then echo ${prog}: missing root-dir parameter. echo $usage exit(1) else if ( ! $?info) then echo ${prog}: missing info-file parameter. echo $usage exit(1) endif # destDir gets default value if unset on command line if ( $?destDir ) then /bin/mkdir -p $destDir else set destDir = . endif # derive the root name for the package from the root name of the info file set root = `/usr/bin/basename $info .info` # create package directory set pkg = ${destDir}/${root}.pkg echo Generating Installer package $pkg ... if ( -e $pkg ) /bin/rm -rf $pkg /bin/mkdir -p -m 755 $pkg # (gnu)tar/pax and compress root directory to package archive echo -n " creating package archive ... " if ( $?fflag ) then set pkgTop = ${rootDir:t} set parent = ${rootDir:h} if ( "$parent" == "$pkgTop" ) set parent = "." else set parent = $rootDir set pkgTop = . endif if ( $?usetar ) then set pkgArchive = $pkg/$root.tar.Z (cd $parent; $tar -w $pkgTop) | /usr/bin/compress -f -c > $pkgArchive else if ( $?usegnutar ) then set pkgArchive = $pkg/$root.tar.gz (cd $parent; $gnutar zcf $pkgArchive $pkgTop) else set pkgArchive = $pkg/$root.pax.gz (cd $parent; $pax -w -z -x cpio $pkgTop) > $pkgArchive endif /bin/chmod 444 $pkgArchive echo done. # copy info file to package set pkgInfo = $pkg/$root.info echo -n " copying ${info:t} ... " /bin/cp $info $pkgInfo /bin/chmod 444 $pkgInfo echo done. # copy tiff file to package if ( $?tiff ) then set pkgTiff = $pkg/$root.tiff echo -n " copying ${tiff:t} ... " /bin/cp $tiff $pkgTiff /bin/chmod 444 $pkgTiff echo done. endif # copy resources to package if ( $?resDir ) then echo -n " copying ${resDir:t} ... " # don't want to see push/pop output pushd $resDir > /dev/null # get lists of resources. We'll want to change # permissions on just these things later. set directoriesInResDir = `find . -type d` set filesInResDir = `find . -type f` popd > /dev/null # copy the resource directory contents into the package directory foreach resFile (`ls $resDir`) cp -r $resDir/$resFile $pkg end pushd $pkg > /dev/null # Change all directories to +r+x, except the package # directory itself foreach resFileItem ($directoriesInResDir) if ( $resFileItem != "." ) then chmod 555 $resFileItem endif end # change all flat files to read only foreach resFileItem ($filesInResDir) chmod 444 $resFileItem end popd > /dev/null echo done. endif # generate bom file set pkgBom = $pkg/$root.bom echo -n " generating bom file ... " /bin/rm -f $pkgBom if ( $?fflag ) then $mkbom $parent $pkgBom >& /dev/null else $mkbom $rootDir $pkgBom >& /dev/null endif /bin/chmod 444 $pkgArchive echo done. # generate sizes file set pkgSizes = $pkg/$root.sizes echo -n " generating sizes file ... " # compute number of files in package set numFiles = `$lsbom -s $pkgBom | /usr/bin/wc -l` # compute package size when compressed @ compressedSize = `/usr/bin/du -k -s $pkg | $awk '{print $1}'` @ compressedSize += 3 # add 1KB each for sizes, location, status files @ infoSize = `/bin/ls -s $pkgInfo | $awk '{print $1}'` @ bomSize = `/bin/ls -s $pkgBom | $awk '{print $1}'` if ( $?tiff ) then @ tiffSize = `/bin/ls -s $pkgTiff | $awk '{print $1}'` else @ tiffSize = 0 endif @ installedSize = `/usr/bin/du -k -s $rootDir | $awk '{print $1}'` @ installedSize += $infoSize + $bomSize + $tiffSize + 3 # echo size parameters to sizes file echo NumFiles $numFiles > $pkgSizes echo InstalledSize $installedSize >> $pkgSizes echo CompressedSize $compressedSize >> $pkgSizes echo done. echo " ... finished generating $pkg." exit(0) # end package