Headless utility classes for making deterministic protocol handlers

headless/public/util/deterministic_dispatcher.cc

Index: headless/public/util/deterministic_dispatcher.cc
diff --git a/headless/public/util/deterministic_dispatcher.cc b/headless/public/util/deterministic_dispatcher.cc
new file mode 100644
index 0000000000000000000000000000000000000000..70696eaeaa98a2736c7c31e7d927f0334328e719
--- /dev/null
+++ b/headless/public/util/deterministic_dispatcher.cc
@@ -0,0 +1,95 @@
+// 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.
+
+#include "headless/public/util/deterministic_dispatcher.h"
+
+#include <utility>
+
+#include "base/bind.h"
+#include "base/logging.h"
+#include "headless/public/util/managed_dispatch_url_request_job.h"
+
+namespace headless {
+
+DeterministicDispatcher::DeterministicDispatcher(
+    scoped_refptr<base::SingleThreadTaskRunner> io_thread_task_runner)
+    : io_thread_task_runner_(std::move(io_thread_task_runner)),
+      dispatch_pending_(false) {}
+
+DeterministicDispatcher::~DeterministicDispatcher() {}
+
+void DeterministicDispatcher::JobCreated(ManagedDispatchURLRequestJob* job) {
+  base::AutoLock lock(lock_);
+  pending_requests_.push_back(job);
+}
+
+void DeterministicDispatcher::JobKilled(ManagedDispatchURLRequestJob* job) {
+  base::AutoLock lock(lock_);
+  for (auto it = pending_requests_.begin(); it != pending_requests_.end();
+       it++) {
+    if (*it == job) {
+      pending_requests_.erase(it);
+      break;
+    }
+  }
+  ready_status_map_.erase(job);
+  // We rely on JobDeleted getting called to call MaybeDispatchJobLocked.
+}
+
+void DeterministicDispatcher::JobFailed(ManagedDispatchURLRequestJob* job,
+                                        net::Error error) {
+  base::AutoLock lock(lock_);
+  ready_status_map_[job] = error;
+  MaybeDispatchJobLocked();
+}
+
+void DeterministicDispatcher::DataReady(ManagedDispatchURLRequestJob* job) {
+  base::AutoLock lock(lock_);
+  ready_status_map_[job] = net::OK;
+  MaybeDispatchJobLocked();
+}
+
+void DeterministicDispatcher::JobDeleted(ManagedDispatchURLRequestJob* job) {
+  base::AutoLock lock(lock_);
+  MaybeDispatchJobLocked();
+}
+
+void DeterministicDispatcher::MaybeDispatchJobLocked() {
+  if (dispatch_pending_ || ready_status_map_.empty())
+    return;
+
+  dispatch_pending_ = true;
+  io_thread_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&DeterministicDispatcher::MaybeDispatchJobOnIOThreadTask,
+                 base::Unretained(this)));
+}
+
+void DeterministicDispatcher::MaybeDispatchJobOnIOThreadTask() {
+  ManagedDispatchURLRequestJob* job;
+  net::Error job_status;
+
+  {
+    base::AutoLock lock(lock_);
+    CHECK(!pending_requests_.empty());
+    dispatch_pending_ = false;
+    job = pending_requests_.front();
+    StatusMap::const_iterator it = ready_status_map_.find(job);
+    // Bail out if the oldest job is not be ready for dispatch yet.
+    if (it == ready_status_map_.end())
+      return;
+
+    job_status = it->second;
+    ready_status_map_.erase(it);
+    pending_requests_.pop_front();
+  }
+
+  if (job_status == net::OK) {
+    job->OnHeadersComplete();
+  } else {
+    job->OnStartError(job_status);
+  }
+}
+
+}  // namespace headless