fix race condition when recording computeCache performance

pkg/analysis_server/lib/src/domain_completion.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library domain.completion;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
@@ skipping 45 matching lines @@
       new List<CompletionPerformance>();
 
   /**
    * The maximum number of performance measurements to keep.
    */
   static const int performanceListMaxLength = 50;
 
   /**
    * Performance for the last priority change event.
    */
-  CompletionPerformance priorityChangedPerformance;
+  CompletionPerformance computeCachePerformance;
 
   /**
    * Initialize a new request handler for the given [server].
    */
   CompletionDomainHandler(this.server) {
     server.onContextsChanged.listen(contextsChanged);
     server.onPriorityChange.listen(priorityChanged);
   }
 
   /**
@@ skipping 52 matching lines @@
     }
     return null;
   }
 
   /**
    * If the set the priority files has changed, then pre-cache completion
    * information related to the first priority file.
    */
   void priorityChanged(PriorityChangeEvent event) {
     Source source = event.firstSource;
-    priorityChangedPerformance = new CompletionPerformance();
-    priorityChangedPerformance.source = source;
-    if (source != null) {
-      AnalysisContext context = server.getAnalysisContextForSource(source);
-      if (context != null) {
-        String computeTag = 'computeCache';
-        priorityChangedPerformance.logStartTime(computeTag);
-        CompletionManager manager = completionManagerFor(context, source);
-        manager.computeCache().then((bool success) {
-          priorityChangedPerformance.logElapseTime(computeTag);
-          priorityChangedPerformance.complete(
-              'priorityChanged caching: $success');
-        });
-        return;
-      }
+    CompletionPerformance performance = new CompletionPerformance();
+    computeCachePerformance = performance;
+    if (source == null) {
+      performance.complete('priorityChanged caching: no source');
+      return;
     }
-    priorityChangedPerformance.complete();
+    performance.source = source;
+    AnalysisContext context = server.getAnalysisContextForSource(source);
+    if (context != null) {
+      String computeTag = 'computeCache';
+      performance.logStartTime(computeTag);
+      CompletionManager manager = completionManagerFor(context, source);
+      manager.computeCache().then((bool success) {
+        performance.logElapseTime(computeTag);
+        performance.complete('priorityChanged caching: $success');
+      });
+    }
   }
 
   /**
    * Process a `completion.getSuggestions` request.
    */
   Response processRequest(Request request) {
     performance = new CompletionPerformance();
     // extract params
     CompletionGetSuggestionsParams params =
         new CompletionGetSuggestionsParams.fromRequest(request);
@@ skipping 31 matching lines @@
         completionId).toResponse(request.id);
   }
 
   /**
    * If tracking code completion performance over time, then
    * record addition information about the request in the performance record.
    */
   void recordRequest(CompletionPerformance performance, AnalysisContext context,
       Source source, int offset) {
     performance.source = source;
-    if (priorityChangedPerformance != null &&
-        priorityChangedPerformance.source != source) {
-      priorityChangedPerformance = null;
-    }
     if (performanceListMaxLength == 0 || context == null || source == null) {
       return;
     }
     TimestampedData<String> data = context.getContents(source);
     if (data == null) {
       return;
     }
     performance.setContentsAndOffset(data.data, offset);
     while (performanceList.length >= performanceListMaxLength) {
       performanceList.removeAt(0);
@@ skipping 45 matching lines @@
     if (_sourcesChangedSubscription != null) {
       _sourcesChangedSubscription.cancel();
       _sourcesChangedSubscription = null;
     }
     if (_manager != null) {
       _manager.dispose();
       _manager = null;
     }
   }
 }