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VideoFrameExtractor: Fix race condition in synchronous extraction mode #1390

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VideoFrameExtractor: Fix race condition in synchronous extraction mode #1390

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2 changes: 2 additions & 0 deletions src/QtAV/VideoFrameExtractor.h
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Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,8 @@ class Q_AV_EXPORT VideoFrameExtractor : public QObject
* Extract video frames in another thread. Default is true.
* In async mode, if current extraction is not finished, new
* setPosition() will be ignored.
* If you want to disable async extraction make sure to call setAsync(false) as soon as possible (before extracting any frames or settings the source).
* After the first frame is extracted setAsync() has no effect.
*/
void setAsync(bool value);
bool async() const;
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40 changes: 23 additions & 17 deletions src/VideoFrameExtractor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -27,8 +27,6 @@
#include <QtCore/QStringList>
#include <QtCore/QThread>
#include <QtCore/QMutex>
#include <QtCore/QMutexLocker>
#include "QtAV/VideoCapture.h"
#include "QtAV/VideoDecoder.h"
#include "QtAV/AVDemuxer.h"
#include "QtAV/Packet.h"
Expand Down Expand Up @@ -369,15 +367,22 @@ class VideoFrameExtractorPrivate : public DPtrPrivate<VideoFrameExtractor>
}

void safeReleaseResource() {
class Cleaner : public QRunnable {
VideoFrameExtractorPrivate *p;
public:
Cleaner(VideoFrameExtractorPrivate* pri) : p(pri) {}
void run() {
p->releaseResourceInternal();
}
};
thread.addTask(new Cleaner(this));
if(!async && !thread.isRunning()) {
releaseResourceInternal();
return;
}

class Cleaner : public QRunnable {
VideoFrameExtractorPrivate *p;
public:
Cleaner(VideoFrameExtractorPrivate* pri) : p(pri) {}
void run() {
p->releaseResourceInternal();
}
};

thread.start();
thread.addTask(new Cleaner(this));
}

volatile bool abort_seek;
Expand All @@ -403,10 +408,7 @@ QVariantHash VideoFrameExtractorPrivate::dec_opt_normal;

VideoFrameExtractor::VideoFrameExtractor(QObject *parent) :
QObject(parent)
{
DPTR_D(VideoFrameExtractor);
d.thread.start();
}
{}

void VideoFrameExtractor::setSource(const QString url)
{
Expand All @@ -430,12 +432,15 @@ void VideoFrameExtractor::setAsync(bool value)
if (d.async == value)
return;
d.async = value;
if (!d.async && d.thread.isRunning()) {
qInfo() << "ExtractThread is already running. Setting async to false has no effect.";
}
Q_EMIT asyncChanged();
}

bool VideoFrameExtractor::async() const
{
return d_func().async;
return d_func().async || d_func().thread.isRunning();
}

void VideoFrameExtractor::setAutoExtract(bool value)
Expand Down Expand Up @@ -494,7 +499,7 @@ int VideoFrameExtractor::precision() const
void VideoFrameExtractor::extract()
{
DPTR_D(VideoFrameExtractor);
if (!d.async) {
if (!d.async && !d.thread.isRunning()) {
extractInternal(position());
return;
}
Expand All @@ -518,6 +523,7 @@ void VideoFrameExtractor::extract()
// (called by extractInternal()) and if true, method returns early.
// Note if seek/decode is aborted, aborted() signal will be emitted.
d.abort_seek = true;
d.thread.start();
d.thread.addTask(new ExtractTask(this, position()));
}

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