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GetPositionSeconds(&tm) returns the clock time timestamp associated with the

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returned sound time.  This is tricky: we may be interrupted, causing timing error.

We tried working around this by trying to hint the scheduler that we're in a
period where we don't want to be interrupted, even though we're in a thread
that's not normally high priority, by boosting the priority temporarily.  This
worked in Windows, but not in general; it's too far out of the expectations of
schedulers and generally just made things worse.

Let's look at this like an interruption-based lockless algorithm: try it, see
if it succeeded, and if it failed, try again.

Retrying even once should be a rare exception, but failsafe anyway, so a bug
in a sound driver won't hang.
This commit is contained in:
Glenn Maynard
2006-12-19 08:00:45 +00:00
parent da93ccefeb
commit 1786d99735
1 changed files with 30 additions and 9 deletions
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stepmania/src/RageSound.cpp
+30 -9
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@@ -26,7 +26,6 @@
#include "RageUtil.h"
#include "RageLog.h"
#include "PrefsManager.h"
#include "arch/ArchHooks/ArchHooks.h"
#include "RageSoundUtil.h"
#include "RageSoundReader_Pan.h"
@@ -656,18 +655,40 @@ float RageSound::GetPositionSeconds( bool *bApproximate, RageTimer *pTimestamp )
{
LockMut( m_Mutex );
if( pTimestamp )
if( pTimestamp == NULL )
{
const int64_t iPositionFrames = GetPositionSecondsInternal( bApproximate );
return iPositionFrames / float(samplerate());
}
/*
* We may have unpredictable scheduling delays between updating the timestamp
* and reading the sound position. If we're preempted while doing this and
* it may have caused the timestamp to not match the returned time, retry.
*
* As a failsafe, only allow a few attempts. If this has to try more than
* a few times, then probably we have thread contention that's causing more
* severe performance problems, anyway.
*/
int iTries = 3;
int64_t iPositionFrames;
do
{
HOOKS->EnterTimeCriticalSection();
pTimestamp->Touch();
iPositionFrames = GetPositionSecondsInternal( bApproximate );
} while( --iTries && pTimestamp->Ago() > 0.002f );
if( iTries == 0 )
{
static bool bLogged = false;
if( !bLogged )
{
bLogged = true;
LOG->Warn( "RageSound::GetPositionSeconds: too many tries" );
}
}
const int64_t iPositionFrames = GetPositionSecondsInternal( bApproximate );
const float fPosition = iPositionFrames / float(samplerate());
if( pTimestamp )
HOOKS->ExitTimeCriticalSection();
return fPosition;
return iPositionFrames / float(samplerate());
}