Fix unload/load bug in Player.

Based on PR #613

There was a bug where calling unload() right before calling load()
would cause a race that would sometimes cause a failure.  This is
because the fields are reset before the unload is complete so the
second call to unload() (from inside load) will complete immediately.

So now we store the unload Promise chain while it is in progress so
we can wait on it from load().

Closes #612

Change-Id: I6c0cdd931827d709fc41322edd51fe10e4aa87ae

lib/player.js

@@ -123,6 +123,9 @@ shaka.Player = function(video, opt_dependencyInjector) {
   /** @private {shaka.util.CancelableChain} */
   this.loadChain_ = null;
 
+  /** @private {Promise} */
+  this.unloadChain_ = null;
+
   /**
    * @private {!Object.<string, {
    *   stream: shakaExtern.Stream,
@@ -177,6 +180,10 @@ shaka.Player.prototype.destroy = function() {
 
   return cancelation.then(function() {
     var p = Promise.all([
+      // We need to destroy the current fields as well as waiting for an
+      // existing unload to complete.  It is fine to call destroyStreaming_ if
+      // there is an unload since it resets the fields immediately.
+      this.unloadChain_,
       this.destroyStreaming_(),
       this.eventManager_ ? this.eventManager_.destroy() : null,
       this.networkingEngine_ ? this.networkingEngine_.destroy() : null
@@ -763,18 +770,24 @@ shaka.Player.prototype.unload = function() {
   if (this.destroyed_) return Promise.resolve();
   this.dispatchEvent(new shaka.util.FakeEvent('unloading'));
 
+  var p = Promise.resolve();
   if (this.loadChain_) {
-    // A load is in progress.  Cancel it, then reset the streaming system.
+    // A load is in progress, cancel it.
     var interrupt = new shaka.util.Error(
         shaka.util.Error.Category.PLAYER,
         shaka.util.Error.Code.LOAD_INTERRUPTED);
-    return this.loadChain_.cancel(interrupt)
-        .then(this.resetStreaming_.bind(this));
-  } else {
-    // No loads or unloads are in progress.
-    // Just reset the streaming system if needed.
-    return this.resetStreaming_();
+    p = this.loadChain_.cancel(interrupt);
   }
+
+  return p.then(function() {
+    // If there is an existing unload operation, use that.
+    if (!this.unloadChain_) {
+      this.unloadChain_ = this.resetStreaming_().then(function() {
+        this.unloadChain_ = null;
+      }.bind(this));
+    }
+    return this.unloadChain_;
+  }.bind(this));
 };
 
 

test/player_unit.js

@@ -123,7 +123,7 @@ describe('Player', function() {
       });
     });
 
-    xit('won\'t start loading until unloading is done', function(done) {
+    it('won\'t start loading until unloading is done', function(done) {
       // There was a bug when calling unload before calling load would cause
       // the load to continue before the (first) unload was complete.
       // https://github.com/google/shaka-player/issues/612