渲染线程flush layer耗时问题

问题背景：

相机场景下调出控制中心，RendThreader有一帧执行renderFrame有较长的 running耗时，

原因分析：

打开trace开关：adb shell setprop persist.sys.hwui.skia_atrace_enabled true)

可以看到异常的一帧flush layer在循环执行 virtual bool GrOpsTask::onExecute(GrOpFlushState *)函数;

bool GrDrawingManager::executeRenderTasks(GrOpFlushState* flushState) {
#if GR_FLUSH_TIME_OP_SPEW
    SkDebugf("Flushing %d opsTasks\n", fDAG.count());
    for (int i = 0; i < fDAG.count(); ++i) {
        if (fDAG[i]) {
            SkString label;
            label.printf("task %d/%d", i, fDAG.count());
            fDAG[i]->dump(label, {}, true, true);
        }
    }
#endif
 
 
    bool anyRenderTasksExecuted = false;
 
 
    for (const auto& renderTask : fDAG) {
        if (!renderTask || !renderTask->isInstantiated()) {
             continue;
        }
 
 
        SkASSERT(renderTask->deferredProxiesAreInstantiated());
 
 
        renderTask->prepare(flushState);
    }
 
 
    // Upload all data to the GPU
    flushState->preExecuteDraws();
 
 
    // For Vulkan, if we have too many oplists to be flushed we end up allocating a lot of resources
    // for each command buffer associated with the oplists. If this gets too large we can cause the
    // devices to go OOM. In practice we usually only hit this case in our tests, but to be safe we
    // put a cap on the number of oplists we will execute before flushing to the GPU to relieve some
    // memory pressure.
    static constexpr int kMaxRenderTasksBeforeFlush = 100;
    int numRenderTasksExecuted = 0;
 
 
    // Execute the onFlush renderTasks first, if any.
    for (sk_sp<GrRenderTask>& onFlushRenderTask : fOnFlushRenderTasks) {
        if (!onFlushRenderTask->execute(flushState)) {
            SkDebugf("WARNING: onFlushRenderTask failed to execute.\n");
        }
        SkASSERT(onFlushRenderTask->unique());
        onFlushRenderTask->disown(this);
        onFlushRenderTask = nullptr;
        if (++numRenderTasksExecuted >= kMaxRenderTasksBeforeFlush) {
            flushState->gpu()->submitToGpu(false);
            numRenderTasksExecuted = 0;
        }
    }
    fOnFlushRenderTasks.reset();
 
 
    // Execute the normal op lists.
    for (const auto& renderTask : fDAG) {
        SkASSERT(renderTask);
        if (!renderTask->isInstantiated()) {
            continue;
        }
 
 
        if (renderTask->execute(flushState)) {
            anyRenderTasksExecuted = true;
        }
        if (++numRenderTasksExecuted >= kMaxRenderTasksBeforeFlush) {
            flushState->gpu()->submitToGpu(false);
            numRenderTasksExecuted = 0;
        }
    }
 
 
    SkASSERT(!flushState->opsRenderPass());
    SkASSERT(fTokenTracker.nextDrawToken() == fTokenTracker.nextTokenToFlush());
 
 
    // We reset the flush state before the RenderTasks so that the last resources to be freed are
    // those that are written to in the RenderTasks. This helps to make sure the most recently used
    // resources are the last to be purged by the resource cache.
    flushState->reset();
 
 
    return anyRenderTasksExecuted;
}

drawPaint()、drawPath()、drawTextBlob()、drawRRect()等多个函数都会添加fDAG数量，fDAG添加路径

异常一帧确定在GrDrawingManager::newOpsTask中添加了fDAG数量。

sk_sp<GrOpsTask> GrDrawingManager::newOpsTask(GrSurfaceProxyView surfaceView,
                                              sk_sp<GrArenas> arenas,
                                              bool flushTimeOpsTask) {
    SkDEBUGCODE(this->validate());
    SkASSERT(fContext);
 
    this->closeActiveOpsTask();
 
    sk_sp<GrOpsTask> opsTask(new GrOpsTask(this,
                                           std::move(surfaceView),
                                           fContext->priv().auditTrail(),
                                           std::move(arenas)));
    SkASSERT(this->getLastRenderTask(opsTask->target(0)) == opsTask.get());
 
    if (flushTimeOpsTask) {
        fOnFlushRenderTasks.push_back(opsTask);
    } else {
        this->appendTask(opsTask);
        fActiveOpsTask = opsTask.get();
    }
 
    SkDEBUGCODE(this->validate());
    return opsTask;
}

执行较长的这一帧，执行onExecute 11次，其中执行int SkCanvas::saveLayer(const SkCanvas::SaveLayerRec &) 2 次，SkGpuDevice::drawDevice 2 次，执行void SkCanvas::drawPaint(const SkPaint &) 7次，一共newOpsTask appendtask 11次，故onExecute执行11次，running时间会比较长