Avoid analysis server crash when reanalyze invoked during analysis.

pkg/analysis_server/lib/src/analysis_server.dart

Index: pkg/analysis_server/lib/src/analysis_server.dart
diff --git a/pkg/analysis_server/lib/src/analysis_server.dart b/pkg/analysis_server/lib/src/analysis_server.dart
index c343d22dae5efd29914ec674b0d9c9bf6e01a76b..d9eea8989ba6e6353864809bc71cbfb639541ad2 100644
--- a/pkg/analysis_server/lib/src/analysis_server.dart
+++ b/pkg/analysis_server/lib/src/analysis_server.dart
@@ -179,11 +179,13 @@ class AnalysisServer {
       new HashMap<Folder, AnalysisContext>();
 
   /**
+   * True if a call to [performOperation] is currently executing, or there is a
+   * pending future which will execute [performOperation].
+   */
+  bool operationLoopRunning = false;
+
+  /**
    * A queue of the operations to perform in this server.
-   *
-   * Invariant: when this queue is non-empty, there is exactly one pending call
-   * to [performOperation] on the event queue.  When this list is empty, there are
-   * no calls to [performOperation] on the event queue.
    */
   ServerOperationQueue operationQueue;
 
@@ -268,10 +270,10 @@ class AnalysisServer {
    * Schedules execution of the given [ServerOperation].
    */
   void scheduleOperation(ServerOperation operation) {
-    bool wasEmpty = operationQueue.isEmpty;
     addOperation(operation);
-    if (wasEmpty) {
+    if (!operationLoopRunning) {
       _schedulePerformOperation();
+      operationLoopRunning = true;
     }
   }
 
@@ -485,15 +487,24 @@ class AnalysisServer {
    * Perform the next available [ServerOperation].
    */
   void performOperation() {
+    assert(operationLoopRunning);
     if (!running) {
       // An error has occurred, or the connection to the client has been
       // closed, since this method was scheduled on the event queue.  So
       // don't do anything.  Instead clear the operation queue.
       operationQueue.clear();
+      operationLoopRunning = false;
       return;
     }
     // prepare next operation
     ServerOperation operation = operationQueue.take();
+    if (operation == null) {
+      // This can happen if the operation queue is cleared while the operation
+      // loop is in progress.  No problem; we just need to exit the operation
+      // loop and wait for the next operation to be added.
+      operationLoopRunning = false;
+      return;
+    }
     sendStatusNotification(operation);
     // perform the operation
     try {
@@ -513,6 +524,7 @@ class AnalysisServer {
       } else {
         sendStatusNotification(null);
         _onAnalysisCompleteController.add(null);
+        operationLoopRunning = false;

[Brian Wilkerson, 2014/10/28 20:37:14]

If an exception occurs in sendStatusNotification, won't this make it impossible
for the server to ever perform another operation?

I think it's safer to change the flag to mean that "there is a pending future
which will execute [performOperation]".

       }
     }
   }