From 644105a4691ffabafb13594aca0c825c92deb8ee Mon Sep 17 00:00:00 2001
From: Kevin Schaaf <kschaaf@google.com>
Date: Mon, 30 Nov 2015 15:01:15 -0800
Subject: [PATCH] Make Polymer.dom.flush reentrant-safe. Fixes #3115.

---
 src/lib/dom-api-flush.html | 22 +++++++++++-----------
 test/unit/polymer-dom.js   | 28 ++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 11 deletions(-)

diff --git a/src/lib/dom-api-flush.html b/src/lib/dom-api-flush.html
index a9e1c6ec5b..618bdd722c 100644
--- a/src/lib/dom-api-flush.html
+++ b/src/lib/dom-api-flush.html
@@ -9,16 +9,16 @@
 -->
 <script>
 
-  /** 
-   * `Polymer.dom.flush()` causes any asynchronously queued actions to be 
+  /**
+   * `Polymer.dom.flush()` causes any asynchronously queued actions to be
    * flushed synchronously. It should be used sparingly as calling it frequently
-   * can negatively impact performance since work is often deferred for 
-   * efficiency. Calling `Polymer.dom.flush()` is useful, for example, when 
-   * an element has to measure itself and is unsure about the state of its 
+   * can negatively impact performance since work is often deferred for
+   * efficiency. Calling `Polymer.dom.flush()` is useful, for example, when
+   * an element has to measure itself and is unsure about the state of its
    * internal or compoased DOM.
    */
   Polymer.Base.extend(Polymer.dom, {
-    
+
     _flushGuard: 0,
     _FLUSH_MAX: 100,
     _needsTakeRecords: !Polymer.Settings.useNativeCustomElements,
@@ -31,8 +31,8 @@
       this._flushGuard = 0;
       this._prepareFlush();
       while (this._debouncers.length && this._flushGuard < this._FLUSH_MAX) {
-        for (var i=0; i < this._debouncers.length; i++) {
-          this._debouncers[i].complete();
+        while (this._debouncers.length) {
+          this._debouncers.shift().complete();
         }
         // clear the list of debouncers
         if (this._finishDebouncer) {
@@ -47,9 +47,9 @@
     },
 
     _prepareFlush: function() {
-      // TODO(sorvell): There is currently not a good way 
+      // TODO(sorvell): There is currently not a good way
       // to process all custom elements mutations under SD polyfill because
-      // these mutations may be inside shadowRoots. 
+      // these mutations may be inside shadowRoots.
       // again make any pending CE mutations that might trigger debouncer
       // additions go...
       if (this._needsTakeRecords) {
@@ -76,7 +76,7 @@
     addDebouncer: function(debouncer) {
       this._debouncers.push(debouncer);
       // ensure the list of active debouncers is cleared when done.
-      this._finishDebouncer = Polymer.Debounce(this._finishDebouncer, 
+      this._finishDebouncer = Polymer.Debounce(this._finishDebouncer,
         this._finishFlush);
     },
 
diff --git a/test/unit/polymer-dom.js b/test/unit/polymer-dom.js
index de6380db14..bf5bd44134 100644
--- a/test/unit/polymer-dom.js
+++ b/test/unit/polymer-dom.js
@@ -635,6 +635,34 @@ suite('Polymer.dom', function() {
 
   });
 
+  test('Polymer.dom.flush reentrancy', function() {
+    // Setup callbacks
+    var order = [];
+    var cb1 = sinon.spy(function() { order.push(cb1); });
+    var cb2 = sinon.spy(function() { order.push(cb2); });
+    var cb3 = sinon.spy(function() { order.push(cb3); });
+    var cb4 = sinon.spy(function() { order.push(cb4); });
+    var cbReentrant = sinon.spy(function() {
+      order.push(cbReentrant);
+      Polymer.dom.addDebouncer(Polymer.Debounce(null, cb3));
+      Polymer.dom.flush();
+      Polymer.dom.addDebouncer(Polymer.Debounce(null, cb4));
+    });
+    // Enqueue debouncers
+    Polymer.dom.addDebouncer(Polymer.Debounce(null, cb1));
+    Polymer.dom.addDebouncer(Polymer.Debounce(null, cbReentrant));
+    Polymer.dom.addDebouncer(Polymer.Debounce(null, cb2));
+    // Flush
+    Polymer.dom.flush();
+    // Check callbacks called and in correct order
+    assert.isTrue(cb1.calledOnce);
+    assert.isTrue(cb2.calledOnce);
+    assert.isTrue(cb3.calledOnce);
+    assert.isTrue(cb4.calledOnce);
+    assert.isTrue(cbReentrant.calledOnce);
+    assert.sameMembers(order, [cb1, cbReentrant, cb2, cb3, cb4]);
+  });
+
 });
 
 suite('Polymer.dom accessors', function() {