Function findHighestPriorityRoot

code/composition/public/app.js:13797–13860

()

  }

  function findHighestPriorityRoot() {
    var highestPriorityWork = NoWork;
    var highestPriorityRoot = null;
    if (lastScheduledRoot !== null) {
      var previousScheduledRoot = lastScheduledRoot;
      var root = firstScheduledRoot;
      while (root !== null) {
        var remainingExpirationTime = root.remainingExpirationTime;
        if (remainingExpirationTime === NoWork) {
          // This root no longer has work. Remove it from the scheduler.

          // TODO: This check is redudant, but Flow is confused by the branch
          // below where we set lastScheduledRoot to null, even though we break
          // from the loop right after.
          !(previousScheduledRoot !== null && lastScheduledRoot !== null) ? invariant(false, 'Should have a previous and last root. This error is likely caused by a bug in React. Please file an issue.') : void 0;
          if (root === root.nextScheduledRoot) {
            // This is the only root in the list.
            root.nextScheduledRoot = null;
            firstScheduledRoot = lastScheduledRoot = null;
            break;
          } else if (root === firstScheduledRoot) {
            // This is the first root in the list.
            var next = root.nextScheduledRoot;
            firstScheduledRoot = next;
            lastScheduledRoot.nextScheduledRoot = next;
            root.nextScheduledRoot = null;
          } else if (root === lastScheduledRoot) {
            // This is the last root in the list.
            lastScheduledRoot = previousScheduledRoot;
            lastScheduledRoot.nextScheduledRoot = firstScheduledRoot;
            root.nextScheduledRoot = null;
            break;
          } else {
            previousScheduledRoot.nextScheduledRoot = root.nextScheduledRoot;
            root.nextScheduledRoot = null;
          }
          root = previousScheduledRoot.nextScheduledRoot;
        } else {
          if (highestPriorityWork === NoWork || remainingExpirationTime < highestPriorityWork) {
            // Update the priority, if it's higher
            highestPriorityWork = remainingExpirationTime;
            highestPriorityRoot = root;
          }
          if (root === lastScheduledRoot) {
            break;
          }
          previousScheduledRoot = root;
          root = root.nextScheduledRoot;
        }
      }
    }

    // If the next root is the same as the previous root, this is a nested
    // update. To prevent an infinite loop, increment the nested update count.
    var previousFlushedRoot = nextFlushedRoot;
    if (previousFlushedRoot !== null && previousFlushedRoot === highestPriorityRoot && highestPriorityWork === Sync) {
      nestedUpdateCount++;
    } else {