diff --git a/src/lib/sw_engine/tvgSwRenderer.cpp b/src/lib/sw_engine/tvgSwRenderer.cpp
index 6a1a8819..e589d618 100644
--- a/src/lib/sw_engine/tvgSwRenderer.cpp
+++ b/src/lib/sw_engine/tvgSwRenderer.cpp
@@ -150,6 +150,9 @@ struct SwShapeTask : SwTask
 
         //Clip Path
         for (auto clip = clips.data; clip < (clips.data + clips.count); ++clip) {
+            //Guarantee composition targets get ready.
+            static_cast<SwShapeTask*>(*clip)->done(tid);
+
             auto clipper = &static_cast<SwShapeTask*>(*clip)->shape;
             //Clip shape rle
             if (shape.rle) {
@@ -202,6 +205,9 @@ struct SwImageTask : SwTask
                 if (!imageGenRle(&image, bbox, false)) goto end;
                 if (image.rle) {
                     for (auto clip = clips.data; clip < (clips.data + clips.count); ++clip) {
+                        //Guarantee composition targets get ready.
+                        static_cast<SwShapeTask*>(*clip)->done(tid);
+
                         auto clipper = &static_cast<SwShapeTask*>(*clip)->shape;
                         if (clipper->fastTrack) rleClipRect(image.rle, &clipper->bbox);
                         else if (clipper->rle) rleClipPath(image.rle, clipper->rle);
@@ -590,13 +596,7 @@ void* SwRenderer::prepareCommon(SwTask* task, const RenderTransform* transform,
     //Finish previous task if it has duplicated request.
     task->done();
 
-    if (clips.count > 0) {
-        //Guarantee composition targets get ready.
-        for (auto clip = clips.data; clip < (clips.data + clips.count); ++clip) {
-            static_cast<SwShapeTask*>(*clip)->done();
-        }
-        task->clips = clips;
-    }
+    if (clips.count > 0) task->clips = clips;
 
     if (transform) {
         if (!task->transform) task->transform = static_cast<Matrix*>(malloc(sizeof(Matrix)));
diff --git a/src/lib/tvgTaskScheduler.cpp b/src/lib/tvgTaskScheduler.cpp
index 79e34a62..6b4b93c5 100644
--- a/src/lib/tvgTaskScheduler.cpp
+++ b/src/lib/tvgTaskScheduler.cpp
@@ -100,13 +100,12 @@ struct TaskQueue {
 };
 
 
-class TaskSchedulerImpl
+struct TaskSchedulerImpl
 {
-public:
-    unsigned                       threadCnt;
+    uint32_t                       threadCnt;
     vector<thread>                 threads;
     vector<TaskQueue>              taskQueues;
-    atomic<unsigned>               idx{0};
+    uint32_t                       idx = 0;
 
     TaskSchedulerImpl(unsigned threadCnt) : threadCnt(threadCnt), taskQueues(threadCnt)
     {
diff --git a/src/lib/tvgTaskScheduler.h b/src/lib/tvgTaskScheduler.h
index 7dd1dce8..8f60903f 100644
--- a/src/lib/tvgTaskScheduler.h
+++ b/src/lib/tvgTaskScheduler.h
@@ -44,20 +44,25 @@ struct Task
 {
 private:
     mutex                   mtx;
-    condition_variable      cv;
-    bool                    ready{true};
-    bool                    pending{false};
+    bool                    finished = true;
+    bool                    running = false;
 
 public:
     virtual ~Task() = default;
 
-    void done()
+    void done(unsigned tid = 0)
     {
-        if (!pending) return;
+        if (finished) return;
 
         unique_lock<mutex> lock(mtx);
-        while (!ready) cv.wait(lock);
-        pending = false;
+
+        if (finished) return;
+
+        //the job hasn't been launched yet.
+        running = true;
+        run(tid);
+        running = false;
+        finished = true;
     }
 
 protected:
@@ -66,17 +71,21 @@ protected:
 private:
     void operator()(unsigned tid)
     {
-        run(tid);
+        if (finished || running) return;
 
         lock_guard<mutex> lock(mtx);
-        ready = true;
-        cv.notify_one();
+
+        if (finished || running) return;
+
+        running = true;
+        run(tid);
+        running = false;
+        finished = true;
     }
 
     void prepare()
     {
-        ready = false;
-        pending = true;
+        finished = false;
     }
 
     friend class TaskSchedulerImpl;