Bug 1069577 - Transfering values with a PromiseWorker. r=froydnj

toolkit/components/promiseworker/PromiseWorker.jsm

@@ -250,21 +250,27 @@ this.BasePromiseWorker.prototype = {
    *   duration of the off main thread execution for this call.
    * @param {*=} closure An object holding references that should not be
    * garbage-collected before the message treatment is complete.
+   * @param {Array=} transfers An array of objects that should be transfered
+   * to the worker instead of being copied. If any of the objects is a Promise,
+   * it is resolved before posting the message.
    *
    * @return {promise}
    */
-  post: function(fun, args, closure) {
+  post: function(fun, args, closure, transfers) {
     return Task.spawn(function* postMessage() {
       // Normalize in case any of the arguments is a promise
       if (args) {
         args = yield Promise.resolve(Promise.all(args));
       }
+      if (transfers) {
+        transfers = yield Promise.resolve(Promise.all(transfers));
+      }
 
       let id = ++this._id;
       let message = {fun: fun, args: args, id: id};
       this.log("Posting message", message);
       try {
-        this._worker.postMessage(message);
+        this._worker.postMessage(message, ...[transfers]);
       } catch (ex if typeof ex == "number") {
         this.log("Could not post message", message, "due to xpcom error", ex);
         // handle raw xpcom errors (see eg bug 961317)

toolkit/components/promiseworker/tests/xpcshell/test_Promise.js

@@ -60,6 +60,26 @@ add_task(function* test_rejected_promise_args() {
   }
 });
 
+add_task(function* test_transfer_args() {
+  let array = new Uint8Array(4);
+  for (let i = 0; i < 4; ++i) {
+    array[i] = i;
+  }
+  Assert.equal(array.buffer.byteLength, 4, "The buffer is not neutered yet");
+
+  let result = (yield worker.post("bounce", [array.buffer], [], [array.buffer]))[0];
+
+  // Check that the buffer has been sent
+  Assert.equal(array.buffer.byteLength, 0, "The buffer has been neutered");
+
+  // Check that the result is correct
+  Assert.equal(result.byteLength, 4, "The result has the right size");
+  let array2 = new Uint8Array(result);
+  for (let i = 0; i < 4; ++i) {
+    Assert.equal(array2[i], i);
+  }
+});
+
 function run_test() {
   run_next_test();
 }