Headless utility classes for making deterministic protocol handlers

headless/public/util/deterministic_dispatcher.h

Index: headless/public/util/deterministic_dispatcher.h
diff --git a/headless/public/util/deterministic_dispatcher.h b/headless/public/util/deterministic_dispatcher.h
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+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef HEADLESS_PUBLIC_UTIL_DETERMINISTIC_DISPATCHER_H_
+#define HEADLESS_PUBLIC_UTIL_DETERMINISTIC_DISPATCHER_H_
+
+#include <deque>
+#include <map>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/single_thread_task_runner.h"
+#include "base/synchronization/lock.h"
+#include "headless/public/util/url_request_dispatcher.h"
+#include "net/base/net_errors.h"
+
+namespace headless {
+
+class ManagedDispatchURLRequestJob;
+
+// The purpose of this class is to queue up calls to OnHeadersComplete and
+// OnStartError and dispatch them in order of URLRequestJob creation. This
+// helps make renders deterministic at the cost of slower page loads.
+class DeterministicDispatcher : public URLRequestDispatcher {
+ public:
+  explicit DeterministicDispatcher(
+      scoped_refptr<base::SingleThreadTaskRunner> io_thread_task_runner);
+
+  ~DeterministicDispatcher() override;
+
+  // UrlRequestDispatcher implementation:
+  void JobCreated(ManagedDispatchURLRequestJob* job) override;
+  void JobKilled(ManagedDispatchURLRequestJob* job) override;
+  void JobFailed(ManagedDispatchURLRequestJob* job, net::Error error) override;
+  void DataReady(ManagedDispatchURLRequestJob* job) override;
+  void JobDeleted(ManagedDispatchURLRequestJob* job) override;
+
+ private:
+  void MaybeDispatchJobLocked();
+  void MaybeDispatchJobOnIOThreadTask();
+
+  scoped_refptr<base::SingleThreadTaskRunner> io_thread_task_runner_;
+
+  // Protects all members below.
+  base::Lock lock_;
+
+  std::deque<ManagedDispatchURLRequestJob*> pending_requests_;
+
+  using StatusMap = std::map<ManagedDispatchURLRequestJob*, net::Error>;
+  StatusMap ready_status_map_;
+
+  // Whether or not a MaybeDispatchJobOnIoThreadTask has been posted on the
+  // |io_thread_task_runner_|
+  bool dispatch_pending_;
+
+  DISALLOW_COPY_AND_ASSIGN(DeterministicDispatcher);
+};
+
+}  // namespace headless
+
+#endif  // HEADLESS_PUBLIC_UTIL_DETERMINISTIC_DISPATCHER_H_