Revert of Straightens outs DEPS in mojo/common

mojo/common/handle_watcher.cc

+// Copyright 2013 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 "mojo/common/handle_watcher.h"
+
+#include <map>
+
+#include "base/atomic_sequence_num.h"
+#include "base/bind.h"
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/memory/singleton.h"
+#include "base/memory/weak_ptr.h"
+#include "base/message_loop/message_loop.h"
+#include "base/single_thread_task_runner.h"
+#include "base/synchronization/lock.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/thread_task_runner_handle.h"
+#include "base/threading/thread.h"
+#include "base/threading/thread_restrictions.h"
+#include "base/time/time.h"
+#include "mojo/common/message_pump_mojo.h"
+#include "mojo/common/message_pump_mojo_handler.h"
+#include "mojo/common/time_helper.h"
+
+namespace mojo {
+namespace common {
+
+typedef int WatcherID;
+
+namespace {
+
+const char kWatcherThreadName[] = "handle-watcher-thread";
+
+base::TimeTicks MojoDeadlineToTimeTicks(MojoDeadline deadline) {
+  return deadline == MOJO_DEADLINE_INDEFINITE ? base::TimeTicks() :
+      internal::NowTicks() + base::TimeDelta::FromMicroseconds(deadline);
+}
+
+// Tracks the data for a single call to Start().
+struct WatchData {
+  WatchData()
+      : id(0), handle_signals(MOJO_HANDLE_SIGNAL_NONE), task_runner(NULL) {}
+
+  WatcherID id;
+  Handle handle;
+  MojoHandleSignals handle_signals;
+  base::TimeTicks deadline;
+  base::Callback<void(MojoResult)> callback;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner;
+};
+
+// WatcherBackend --------------------------------------------------------------
+
+// WatcherBackend is responsible for managing the requests and interacting with
+// MessagePumpMojo. All access (outside of creation/destruction) is done on the
+// thread WatcherThreadManager creates.
+class WatcherBackend : public MessagePumpMojoHandler {
+ public:
+  WatcherBackend();
+  ~WatcherBackend() override;
+
+  void StartWatching(const WatchData& data);
+
+  // Cancels a previously scheduled request to start a watch.
+  void StopWatching(WatcherID watcher_id);
+
+ private:
+  typedef std::map<Handle, WatchData> HandleToWatchDataMap;
+
+  // Invoked when a handle needs to be removed and notified.
+  void RemoveAndNotify(const Handle& handle, MojoResult result);
+
+  // Searches through |handle_to_data_| for |watcher_id|. Returns true if found
+  // and sets |handle| to the Handle. Returns false if not a known id.
+  bool GetMojoHandleByWatcherID(WatcherID watcher_id, Handle* handle) const;
+
+  // MessagePumpMojoHandler overrides:
+  void OnHandleReady(const Handle& handle) override;
+  void OnHandleError(const Handle& handle, MojoResult result) override;
+
+  // Maps from assigned id to WatchData.
+  HandleToWatchDataMap handle_to_data_;
+
+  DISALLOW_COPY_AND_ASSIGN(WatcherBackend);
+};
+
+WatcherBackend::WatcherBackend() {
+}
+
+WatcherBackend::~WatcherBackend() {
+}
+
+void WatcherBackend::StartWatching(const WatchData& data) {
+  RemoveAndNotify(data.handle, MOJO_RESULT_CANCELLED);
+
+  DCHECK_EQ(0u, handle_to_data_.count(data.handle));
+
+  handle_to_data_[data.handle] = data;
+  MessagePumpMojo::current()->AddHandler(this, data.handle,
+                                         data.handle_signals,
+                                         data.deadline);
+}
+
+void WatcherBackend::StopWatching(WatcherID watcher_id) {
+  // Because of the thread hop it is entirely possible to get here and not
+  // have a valid handle registered for |watcher_id|.
+  Handle handle;
+  if (GetMojoHandleByWatcherID(watcher_id, &handle)) {
+    handle_to_data_.erase(handle);
+    MessagePumpMojo::current()->RemoveHandler(handle);
+  }
+}
+
+void WatcherBackend::RemoveAndNotify(const Handle& handle,
+                                     MojoResult result) {
+  if (handle_to_data_.count(handle) == 0)
+    return;
+
+  const WatchData data(handle_to_data_[handle]);
+  handle_to_data_.erase(handle);
+  MessagePumpMojo::current()->RemoveHandler(handle);
+
+  data.task_runner->PostTask(FROM_HERE, base::Bind(data.callback, result));
+}
+
+bool WatcherBackend::GetMojoHandleByWatcherID(WatcherID watcher_id,
+                                              Handle* handle) const {
+  for (HandleToWatchDataMap::const_iterator i = handle_to_data_.begin();
+       i != handle_to_data_.end(); ++i) {
+    if (i->second.id == watcher_id) {
+      *handle = i->second.handle;
+      return true;
+    }
+  }
+  return false;
+}
+
+void WatcherBackend::OnHandleReady(const Handle& handle) {
+  RemoveAndNotify(handle, MOJO_RESULT_OK);
+}
+
+void WatcherBackend::OnHandleError(const Handle& handle, MojoResult result) {
+  RemoveAndNotify(handle, result);
+}
+
+// WatcherThreadManager --------------------------------------------------------
+
+// WatcherThreadManager manages the background thread that listens for handles
+// to be ready. All requests are handled by WatcherBackend.
+}  // namespace
+
+class WatcherThreadManager {
+ public:
+  ~WatcherThreadManager();
+
+  // Returns the shared instance.
+  static WatcherThreadManager* GetInstance();
+
+  // Starts watching the requested handle. Returns a unique ID that is used to
+  // stop watching the handle. When the handle is ready |callback| is notified
+  // on the thread StartWatching() was invoked on.
+  // This may be invoked on any thread.
+  WatcherID StartWatching(const Handle& handle,
+                          MojoHandleSignals handle_signals,
+                          base::TimeTicks deadline,
+                          const base::Callback<void(MojoResult)>& callback);
+
+  // Stops watching a handle.
+  // This may be invoked on any thread.
+  void StopWatching(WatcherID watcher_id);
+
+ private:
+  enum RequestType {
+    REQUEST_START,
+    REQUEST_STOP,
+  };
+
+  // See description of |requests_| for details.
+  struct RequestData {
+    RequestData() : type(REQUEST_START), stop_id(0), stop_event(NULL) {}
+
+    RequestType type;
+    WatchData start_data;
+    WatcherID stop_id;
+    base::WaitableEvent* stop_event;
+  };
+
+  typedef std::vector<RequestData> Requests;
+
+  friend struct DefaultSingletonTraits<WatcherThreadManager>;
+
+  WatcherThreadManager();
+
+  // Schedules a request on the background thread. See |requests_| for details.
+  void AddRequest(const RequestData& data);
+
+  // Processes requests added to |requests_|. This is invoked on the backend
+  // thread.
+  void ProcessRequestsOnBackendThread();
+
+  base::Thread thread_;
+
+  base::AtomicSequenceNumber watcher_id_generator_;
+
+  WatcherBackend backend_;
+
+  // Protects |requests_|.
+  base::Lock lock_;
+
+  // Start/Stop result in adding a RequestData to |requests_| (protected by
+  // |lock_|). When the background thread wakes up it processes the requests.
+  Requests requests_;
+
+  DISALLOW_COPY_AND_ASSIGN(WatcherThreadManager);
+};
+
+WatcherThreadManager::~WatcherThreadManager() {
+  thread_.Stop();
+}
+
+WatcherThreadManager* WatcherThreadManager::GetInstance() {
+  return Singleton<WatcherThreadManager>::get();
+}
+
+WatcherID WatcherThreadManager::StartWatching(
+    const Handle& handle,
+    MojoHandleSignals handle_signals,
+    base::TimeTicks deadline,
+    const base::Callback<void(MojoResult)>& callback) {
+  RequestData request_data;
+  request_data.type = REQUEST_START;
+  request_data.start_data.id = watcher_id_generator_.GetNext();
+  request_data.start_data.handle = handle;
+  request_data.start_data.callback = callback;
+  request_data.start_data.handle_signals = handle_signals;
+  request_data.start_data.deadline = deadline;
+  request_data.start_data.task_runner = base::ThreadTaskRunnerHandle::Get();
+  AddRequest(request_data);
+  return request_data.start_data.id;
+}
+
+void WatcherThreadManager::StopWatching(WatcherID watcher_id) {
+  // Handle the case of StartWatching() followed by StopWatching() before
+  // |thread_| woke up.
+  {
+    base::AutoLock auto_lock(lock_);
+    for (Requests::iterator i = requests_.begin(); i != requests_.end(); ++i) {
+      if (i->type == REQUEST_START && i->start_data.id == watcher_id) {
+        // Watcher ids are not reused, so if we find it we can stop.
+        requests_.erase(i);
+        return;
+      }
+    }
+  }
+
+  base::ThreadRestrictions::ScopedAllowWait allow_wait;
+  base::WaitableEvent event(true, false);
+  RequestData request_data;
+  request_data.type = REQUEST_STOP;
+  request_data.stop_id = watcher_id;
+  request_data.stop_event = &event;
+  AddRequest(request_data);
+
+  // We need to block until the handle is actually removed.
+  event.Wait();
+}
+
+void WatcherThreadManager::AddRequest(const RequestData& data) {
+  {
+    base::AutoLock auto_lock(lock_);
+    const bool was_empty = requests_.empty();
+    requests_.push_back(data);
+    if (!was_empty)
+      return;
+  }
+  // We own |thread_|, so it's safe to use Unretained() here.
+  thread_.task_runner()->PostTask(
+      FROM_HERE,
+      base::Bind(&WatcherThreadManager::ProcessRequestsOnBackendThread,
+                 base::Unretained(this)));
+}
+
+void WatcherThreadManager::ProcessRequestsOnBackendThread() {
+  DCHECK_EQ(thread_.message_loop(), base::MessageLoop::current());
+
+  Requests requests;
+  {
+    base::AutoLock auto_lock(lock_);
+    requests_.swap(requests);
+  }
+  for (size_t i = 0; i < requests.size(); ++i) {
+    if (requests[i].type == REQUEST_START) {
+      backend_.StartWatching(requests[i].start_data);
+    } else {
+      backend_.StopWatching(requests[i].stop_id);
+      requests[i].stop_event->Signal();
+    }
+  }
+}
+
+WatcherThreadManager::WatcherThreadManager()
+    : thread_(kWatcherThreadName) {
+  base::Thread::Options thread_options;
+  thread_options.message_pump_factory = base::Bind(&MessagePumpMojo::Create);
+  thread_.StartWithOptions(thread_options);
+}
+
+// HandleWatcher::StateBase and subclasses -------------------------------------
+
+// The base class of HandleWatcher's state. Owns the user's callback and
+// monitors the current thread's MessageLoop to know when to force the callback
+// to run (with an error) even though the pipe hasn't been signaled yet.
+class HandleWatcher::StateBase : public base::MessageLoop::DestructionObserver {
+ public:
+  StateBase(HandleWatcher* watcher,
+            const base::Callback<void(MojoResult)>& callback)
+      : watcher_(watcher),
+        callback_(callback),
+        got_ready_(false) {
+    base::MessageLoop::current()->AddDestructionObserver(this);
+  }
+
+  ~StateBase() override {
+    base::MessageLoop::current()->RemoveDestructionObserver(this);
+  }
+
+ protected:
+  void NotifyHandleReady(MojoResult result) {
+    got_ready_ = true;
+    NotifyAndDestroy(result);
+  }
+
+  bool got_ready() const { return got_ready_; }
+
+ private:
+  void WillDestroyCurrentMessageLoop() override {
+    // The current thread is exiting. Simulate a watch error.
+    NotifyAndDestroy(MOJO_RESULT_ABORTED);
+  }
+
+  void NotifyAndDestroy(MojoResult result) {
+    base::Callback<void(MojoResult)> callback = callback_;
+    watcher_->Stop();  // Destroys |this|.
+
+    callback.Run(result);
+  }
+
+  HandleWatcher* watcher_;
+  base::Callback<void(MojoResult)> callback_;
+
+  // Have we been notified that the handle is ready?
+  bool got_ready_;
+
+  DISALLOW_COPY_AND_ASSIGN(StateBase);
+};
+
+// If the thread on which HandleWatcher is used runs MessagePumpMojo,
+// SameThreadWatchingState is used to directly watch the handle on the same
+// thread.
+class HandleWatcher::SameThreadWatchingState : public StateBase,
+                                               public MessagePumpMojoHandler {
+ public:
+  SameThreadWatchingState(HandleWatcher* watcher,
+                          const Handle& handle,
+                          MojoHandleSignals handle_signals,
+                          MojoDeadline deadline,
+                          const base::Callback<void(MojoResult)>& callback)
+      : StateBase(watcher, callback),
+        handle_(handle) {
+    DCHECK(MessagePumpMojo::IsCurrent());
+
+    MessagePumpMojo::current()->AddHandler(
+        this, handle, handle_signals, MojoDeadlineToTimeTicks(deadline));
+  }
+
+  ~SameThreadWatchingState() override {
+    if (!got_ready())
+      MessagePumpMojo::current()->RemoveHandler(handle_);
+  }
+
+ private:
+  // MessagePumpMojoHandler overrides:
+  void OnHandleReady(const Handle& handle) override {
+    StopWatchingAndNotifyReady(handle, MOJO_RESULT_OK);
+  }
+
+  void OnHandleError(const Handle& handle, MojoResult result) override {
+    StopWatchingAndNotifyReady(handle, result);
+  }
+
+  void StopWatchingAndNotifyReady(const Handle& handle, MojoResult result) {
+    DCHECK_EQ(handle.value(), handle_.value());
+    MessagePumpMojo::current()->RemoveHandler(handle_);
+    NotifyHandleReady(result);
+  }
+
+  Handle handle_;
+
+  DISALLOW_COPY_AND_ASSIGN(SameThreadWatchingState);
+};
+
+// If the thread on which HandleWatcher is used runs a message pump different
+// from MessagePumpMojo, SecondaryThreadWatchingState is used to watch the
+// handle on the handle watcher thread.
+class HandleWatcher::SecondaryThreadWatchingState : public StateBase {
+ public:
+  SecondaryThreadWatchingState(HandleWatcher* watcher,
+                               const Handle& handle,
+                               MojoHandleSignals handle_signals,
+                               MojoDeadline deadline,
+                               const base::Callback<void(MojoResult)>& callback)
+      : StateBase(watcher, callback),
+        weak_factory_(this) {
+    watcher_id_ = WatcherThreadManager::GetInstance()->StartWatching(
+        handle,
+        handle_signals,
+        MojoDeadlineToTimeTicks(deadline),
+        base::Bind(&SecondaryThreadWatchingState::NotifyHandleReady,
+                   weak_factory_.GetWeakPtr()));
+  }
+
+  ~SecondaryThreadWatchingState() override {
+    // If we've been notified the handle is ready (|got_ready()| is true) then
+    // the watch has been implicitly removed by
+    // WatcherThreadManager/MessagePumpMojo and we don't have to call
+    // StopWatching(). To do so would needlessly entail posting a task and
+    // blocking until the background thread services it.
+    if (!got_ready())
+      WatcherThreadManager::GetInstance()->StopWatching(watcher_id_);
+  }
+
+ private:
+  WatcherID watcher_id_;
+
+  // Used to weakly bind |this| to the WatcherThreadManager.
+  base::WeakPtrFactory<SecondaryThreadWatchingState> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(SecondaryThreadWatchingState);
+};
+
+// HandleWatcher ---------------------------------------------------------------
+
+HandleWatcher::HandleWatcher() {
+}
+
+HandleWatcher::~HandleWatcher() {
+}
+
+void HandleWatcher::Start(const Handle& handle,
+                          MojoHandleSignals handle_signals,
+                          MojoDeadline deadline,
+                          const base::Callback<void(MojoResult)>& callback) {
+  DCHECK(handle.is_valid());
+  DCHECK_NE(MOJO_HANDLE_SIGNAL_NONE, handle_signals);
+
+  // Need to clear the state before creating a new one.
+  state_.reset();
+  if (MessagePumpMojo::IsCurrent()) {
+    state_.reset(new SameThreadWatchingState(
+        this, handle, handle_signals, deadline, callback));
+  } else {
+    state_.reset(new SecondaryThreadWatchingState(
+        this, handle, handle_signals, deadline, callback));
+  }
+}
+
+void HandleWatcher::Stop() {
+  state_.reset();
+}
+
+}  // namespace common
+}  // namespace mojo