1 files changed, 73 insertions, 0 deletions
diff --git a/gfx/layers/ipc/SynchronousTask.h b/gfx/layers/ipc/SynchronousTask.h
new file mode 100644
index 0000000000..06f14caafc
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+++ b/gfx/layers/ipc/SynchronousTask.h
@@ -0,0 +1,73 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_GFX_SYNCHRONOUSTASK_H
+#define MOZILLA_GFX_SYNCHRONOUSTASK_H
+
+#include "mozilla/ReentrantMonitor.h"  // for ReentrantMonitor, etc
+
+namespace mozilla {
+namespace layers {
+
+// Helper that creates a monitor and a "done" flag, then enters the monitor.
+class MOZ_STACK_CLASS SynchronousTask {
+  friend class AutoCompleteTask;
+
+ public:
+  explicit SynchronousTask(const char* name)
+      : mMonitor(name), mAutoEnter(mMonitor), mDone(false) {}
+
+  nsresult Wait(PRIntervalTime aInterval = PR_INTERVAL_NO_TIMEOUT) {
+    // For indefinite timeouts, wait in a while loop to handle spurious
+    // wakeups.
+    while (aInterval == PR_INTERVAL_NO_TIMEOUT && !mDone) {
+      mMonitor.Wait();
+    }
+
+    // For finite timeouts, we only check once for completion, and otherwise
+    // rely on the ReentrantMonitor to manage the interval. If the monitor
+    // returns too early, we'll never know, but we can check if the mDone
+    // flag was set to true, indicating that the task finished successfully.
+    if (!mDone) {
+      // We ignore the return value from ReentrantMonitor::Wait, because it's
+      // always NS_OK, even in the case of timeout.
+      mMonitor.Wait(aInterval);
+
+      if (!mDone) {
+        return NS_ERROR_ABORT;
+      }
+    }
+
+    return NS_OK;
+  }
+
+ private:
+  void Complete() {
+    mDone = true;
+    mMonitor.NotifyAll();
+  }
+
+ private:
+  ReentrantMonitor mMonitor MOZ_UNANNOTATED;
+  ReentrantMonitorAutoEnter mAutoEnter;
+  bool mDone;
+};
+
+class MOZ_STACK_CLASS AutoCompleteTask final {
+ public:
+  explicit AutoCompleteTask(SynchronousTask* aTask)
+      : mTask(aTask), mAutoEnter(aTask->mMonitor) {}
+  ~AutoCompleteTask() { mTask->Complete(); }
+
+ private:
+  SynchronousTask* mTask;
+  ReentrantMonitorAutoEnter mAutoEnter;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif