common taskscheduler: revert 4db25db962

There is a report of the thread sanitizer.
It could be a false-positive as far as I reviewed,
but we hate to be bothered by it. So let's revert it.

@Issue: https://github.com/thorvg/thorvg/issues/1409

src/lib/sw_engine/tvgSwRenderer.cpp

@@ -173,8 +173,6 @@ struct SwShapeTask : SwTask
         //Clip Path
         for (auto clip = clips.data; clip < (clips.data + clips.count); ++clip) {
             auto clipper = static_cast<SwTask*>(*clip);
-            //Guarantee composition targets get ready.
-            clipper->done(tid);
             //Clip shape rle
             if (shape.rle && !clipper->clip(shape.rle)) goto err;
             //Clip stroke rle
@@ -225,25 +223,17 @@ struct SwSceneTask : SwTask
         if (!sceneRle) sceneRle = static_cast<SwRleData*>(calloc(1, sizeof(SwRleData)));
         else rleReset(sceneRle);
 
-        //Only one shape
-        if (scene.count == 1) {
-            auto clipper = static_cast<SwTask*>(*scene.data);
-            clipper->done(tid);
         //Merge shapes if it has more than one shapes
-        } else {
+        if (scene.count > 1) {
             //Merge first two clippers
             auto clipper1 = static_cast<SwTask*>(*scene.data);
-            clipper1->done(tid);
-
             auto clipper2 = static_cast<SwTask*>(*(scene.data + 1));
-            clipper2->done(tid);
 
             rleMerge(sceneRle, clipper1->rle(), clipper2->rle());
 
             //Unify the remained clippers
             for (auto rd = scene.data + 2; rd < (scene.data + scene.count); ++rd) {
                 auto clipper = static_cast<SwTask*>(*rd);
-                clipper->done(tid);
                 rleMerge(sceneRle, sceneRle, clipper->rle());
             }
         }
@@ -305,8 +295,6 @@ struct SwImageTask : SwTask
                     imageDelOutline(&image, mpool, tid);
                     for (auto clip = clips.data; clip < (clips.data + clips.count); ++clip) {
                         auto clipper = static_cast<SwTask*>(*clip);
-                        //Guarantee composition targets get ready.
-                        clipper->done(tid);
                         if (!clipper->clip(image.rle)) goto err;
                     }
                     return;
@@ -697,6 +685,15 @@ void* SwRenderer::prepareCommon(SwTask* task, const RenderTransform* transform,
     //Finish previous task if it has duplicated request.
     task->done();
 
+    //TODO: Failed threading them. It would be better if it's possible.
+    //See: https://github.com/thorvg/thorvg/issues/1409
+    if (clips.count > 0) {
+        //Guarantee composition targets get ready.
+        for (auto clip = clips.data; clip < (clips.data + clips.count); ++clip) {
+            static_cast<SwTask*>(*clip)->done();
+        }
+    }
+
     task->clips = clips;
 
     if (transform) {

src/lib/tvgTaskScheduler.h

@@ -43,77 +43,40 @@ struct TaskScheduler
 struct Task
 {
 private:
-    mutex                   finishedMtx;
+    mutex                   mtx;
-    mutex                   preparedMtx;
     condition_variable      cv;
-    bool                    finished = true;        //if run() finished
+    bool                    ready = true;
-    bool                    prepared = false;       //the task is requested
+    bool                    pending = false;
 
 public:
-    virtual ~Task()
+    virtual ~Task() = default;
-    {
-        if (!prepared) return;
-
-        //Guarantee the task is finished by TaskScheduler.
-        unique_lock<mutex> lock(preparedMtx);
-
-        while (prepared) {
-            cv.wait(lock);
-        }
-    }
 
     void done(unsigned tid = 0)
     {
-        if (finished) return;
+        if (!pending) return;
 
-        lock_guard<mutex> lock(finishedMtx);
+        unique_lock<mutex> lock(mtx);
-
+        while (!ready) cv.wait(lock);
-        if (finished) return;
+        pending = false;
-
-        //the job hasn't been launched yet.
-
-        //set finished so that operator() quickly returns.
-        finished = true;
-
-        run(tid);
     }
 
 protected:
     virtual void run(unsigned tid) = 0;
 
 private:
-    void finish()
-    {
-        lock_guard<mutex> lock(preparedMtx);
-        prepared = false;
-        cv.notify_one();
-    }
-
     void operator()(unsigned tid)
     {
-        if (finished) {
-            finish();
-            return;
-        }
-
-        lock_guard<mutex> lock(finishedMtx);
-
-        if (finished) {
-            finish();
-            return;
-        }
-
         run(tid);
 
-        finished = true;
+        lock_guard<mutex> lock(mtx);
-
+        ready = true;
-        finish();
+        cv.notify_one();
     }
 
     void prepare()
     {
-        finished = false;
+        ready = false;
-        prepared = true;
+        pending = true;
     }
 
     friend struct TaskSchedulerImpl;