Move running tasks for fixed time to the scheduler.

pkg/analyzer/lib/src/dart/analysis/driver.dart

Index: pkg/analyzer/lib/src/dart/analysis/driver.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/driver.dart b/pkg/analyzer/lib/src/dart/analysis/driver.dart
index a84d458d3313eb9c5b74f2d59c6ea23cce8730fc..35698f9a36e22ef0660de51e65f42513d2bb535a 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -977,6 +977,7 @@ class AnalysisDriverScheduler {
    * priority first.
    */
   Future<Null> _run() async {
+    Stopwatch timer = new Stopwatch()..start();
     PerformanceLogSection analysisSection;
     while (true) {
       // Pump the event queue to allow IO and other asynchronous data
@@ -988,7 +989,14 @@ class AnalysisDriverScheduler {
       // analysis or other data processing tasks are starving. Ideally we
       // would need to be able to set priority of (continuous) asynchronous
       // tasks.
-      await _pumpEventQueue(128);
+      //
+      // Relinquishing execution flow and running event loop after every task
+      // has too much overhead. Instead we use a fixed length of time, so we
+      // can spend less time overall and still respond quick enough.
+      if (timer.elapsedMilliseconds > 2) {

[Brian Wilkerson, 2016/12/01 14:36:38]

I think it would be a good thing to define some constants for the values used to
control this code, moving the comments above into the comments for the
constants, so that we could more easily find where to change the code in order
to experiment with optimizing these values.

[scheglov, 2016/12/01 16:55:06]

Done.

+        await _pumpEventQueue(128);
+        timer.reset();
+      }
 
       await _hasWork.signal;
 
@@ -1266,37 +1274,30 @@ class _FilesReferencingNameTask {
   _FilesReferencingNameTask(this.driver, this.name);
 
   /**
-   * Perform work for a fixed length of time, and either complete the
-   * [completer] and return `true` to indicate that the task is done, return
-   * `false` to indicate that the task should continue to be run.
-   *
-   * Relinquishing execution flow and running event loop after every file
-   * works, but has too much overhead. Instead we use a fixed length of time,
-   * so we can spend less time overall and keep quick enough response time.
+   * Perform a single piece of work, and either complete the [completer] and
+   * return `true` to indicate that the task is done, return `false` to indicate
+   * that the task should continue to be run.
    */
   Future<bool> perform() async {
-    Stopwatch timer = new Stopwatch()..start();
-    while (timer.elapsedMilliseconds < 5) {
-      // Prepare files to check.
-      if (filesToCheck.isEmpty) {
-        Set<String> newFiles = driver.addedFiles.difference(checkedFiles);
-        filesToCheck.addAll(newFiles);
-      }
+    // Prepare files to check.
+    if (filesToCheck.isEmpty) {
+      Set<String> newFiles = driver.addedFiles.difference(checkedFiles);
+      filesToCheck.addAll(newFiles);
+    }
 
-      // If no more files to check, complete and done.
-      if (filesToCheck.isEmpty) {
-        completer.complete(referencingFiles);
-        return true;
-      }
+    // If no more files to check, complete and done.
+    if (filesToCheck.isEmpty) {
+      completer.complete(referencingFiles);
+      return true;
+    }
 
-      // Check the next file.
-      String path = filesToCheck.removeLast();
-      FileState file = driver._fsState.getFileForPath(path);
-      if (file.referencedNames.contains(name)) {
-        referencingFiles.add(path);
-      }
-      checkedFiles.add(path);
+    // Check the next file.
+    String path = filesToCheck.removeLast();
+    FileState file = driver._fsState.getFileForPath(path);
+    if (file.referencedNames.contains(name)) {
+      referencingFiles.add(path);
     }
+    checkedFiles.add(path);
 
     // We're not done yet.
     return false;