Bug 912457 - Expose async |flush()| in OS.File. r=yoric

toolkit/components/osfile/modules/osfile_async_front.jsm

@@ -485,6 +485,22 @@ File.prototype = {
   setPosition: function setPosition(pos, whence) {
     return Scheduler.post("File_prototype_setPosition",
       [this._fdmsg, pos, whence]);
+  },
+
+  /**
+   * Flushes the file's buffers and causes all buffered data
+   * to be written.
+   * Disk flushes are very expensive and therefore should be used carefully,
+   * sparingly and only in scenarios where it is vital that data survives
+   * system crashes. Even though the function will be executed off the
+   * main-thread, it might still affect the overall performance of any running
+   * application.
+   *
+   * @return {promise}
+   */
+  flush: function flush() {
+    return Scheduler.post("File_prototype_flush",
+      [this._fdmsg]);
   }
 };
 

toolkit/components/osfile/modules/osfile_async_worker.js

@@ -408,6 +408,12 @@ if (this.Components) {
          return this.getPosition();
        });
    },
+   File_prototype_flush: function flush(fd) {
+     return withFile(fd,
+       function do_flush() {
+         return this.flush();
+       });
+   },
    // Methods of OS.File.DirectoryIterator
    DirectoryIterator_prototype_next: function next(dir) {
      return withDir(dir,

toolkit/components/osfile/modules/osfile_unix_front.jsm

@@ -171,6 +171,11 @@
      /**
       * Flushes the file's buffers and causes all buffered data
       * to be written.
+      * Disk flushes are very expensive and therefore should be used carefully,
+      * sparingly and only in scenarios where it is vital that data survives
+      * system crashes. Even though the function will be executed off the
+      * main-thread, it might still affect the overall performance of any
+      * running application.
       *
       * @throws {OS.File.Error} In case of I/O error.
       */

toolkit/components/osfile/modules/osfile_win_front.jsm

@@ -191,6 +191,11 @@
      /**
       * Flushes the file's buffers and causes all buffered data
       * to be written.
+      * Disk flushes are very expensive and therefore should be used carefully,
+      * sparingly and only in scenarios where it is vital that data survives
+      * system crashes. Even though the function will be executed off the
+      * main-thread, it might still affect the overall performance of any
+      * running application.
       *
       * @throws {OS.File.Error} In case of I/O error.
       */

toolkit/components/osfile/tests/xpcshell/test_osfile_async_flush.js

@@ -0,0 +1,30 @@
+"use strict";
+
+Components.utils.import("resource://gre/modules/osfile.jsm");
+Components.utils.import("resource://gre/modules/Task.jsm");
+
+function run_test() {
+  do_test_pending();
+  run_next_test();
+}
+
+/**
+ * Test to ensure that |File.prototype.flush| is available in the async API.
+ */
+
+add_task(function test_flush() {
+  let path = OS.Path.join(OS.Constants.Path.tmpDir,
+                          "test_osfile_async_flush.tmp");
+  let file = yield OS.File.open(path, {trunc: true, write: true});
+  try {
+    try {
+      yield file.flush();
+    } finally {
+      yield file.close();
+    }
+  } finally {
+    yield OS.File.remove(path);
+  }
+});
+
+add_task(do_test_finished);

toolkit/components/osfile/tests/xpcshell/xpcshell.ini

@@ -8,6 +8,7 @@ tail =
 [test_osfile_async_append.js]
 [test_osfile_async_bytes.js]
 [test_osfile_async_copy.js]
+[test_osfile_async_flush.js]
 [test_profiledir.js]
 [test_logging.js]
 [test_creationDate.js]