初窥React-10 (render引)

　　浏览performSyncWorkOnRoot 方法,根据不同情况进行渲染，这里是workInProgress和没有开始的

if (root === workInProgressRoot && includesSomeLane(root.expiredLanes, workInProgressRootRenderLanes)) {
      // There's a partial tree, and at least one of its lanes has expired. Finish
      // rendering it before rendering the rest of the expired work.
      lanes = workInProgressRootRenderLanes;
      exitStatus = renderRootSync(root, lanes);

      if (includesSomeLane(workInProgressRootIncludedLanes, workInProgressRootUpdatedLanes)) {
        // The render included lanes that were updated during the render phase.
        // For example, when unhiding a hidden tree, we include all the lanes
        // that were previously skipped when the tree was hidden. That set of
        // lanes is a superset of the lanes we started rendering with.
        //
        // Note that this only happens when part of the tree is rendered
        // concurrently. If the whole tree is rendered synchronously, then there
        // are no interleaved events.
        lanes = getNextLanes(root, lanes);
        exitStatus = renderRootSync(root, lanes);
      }
    } else {
      lanes = getNextLanes(root, NoLanes);
      exitStatus = renderRootSync(root, lanes);
    }

 

　　刨除掉非主要代码以外，来到了commit代码，这个后面慢慢分析

 var finishedWork = root.current.alternate;
    root.finishedWork = finishedWork;
    root.finishedLanes = lanes;
    commitRoot(root); // Before exiting, make sure there's a callback scheduled for the next
    // pending level.

    ensureRootIsScheduled(root, now());
    return null;