mojo/common/handle_watcher.cc

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "mojo/common/handle_watcher.h"
   6
   7 #include <map>
   8
   9 #include "base/atomic_sequence_num.h"
  10 #include "base/bind.h"
  11 #include "base/lazy_instance.h"
  12 #include "base/logging.h"
  13 #include "base/macros.h"
  14 #include "base/memory/singleton.h"
  15 #include "base/memory/weak_ptr.h"
  16 #include "base/message_loop/message_loop.h"
  17 #include "base/single_thread_task_runner.h"
  18 #include "base/synchronization/lock.h"
  19 #include "base/synchronization/waitable_event.h"
  20 #include "base/thread_task_runner_handle.h"
  21 #include "base/threading/thread.h"
  22 #include "base/threading/thread_restrictions.h"
  23 #include "base/time/time.h"
  24 #include "mojo/common/message_pump_mojo.h"
  25 #include "mojo/common/message_pump_mojo_handler.h"
  26 #include "mojo/common/time_helper.h"
  27
  28 namespace mojo {
  29 namespace common {
  30
  31 typedef int WatcherID;
  32
  33 namespace {
  34
  35 const char kWatcherThreadName[] = "handle-watcher-thread";
  36
  37 base::TimeTicks MojoDeadlineToTimeTicks(MojoDeadline deadline) {
  38   return deadline == MOJO_DEADLINE_INDEFINITE ? base::TimeTicks() :
  39       internal::NowTicks() + base::TimeDelta::FromMicroseconds(deadline);
  40 }
  41
  42 // Tracks the data for a single call to Start().
  43 struct WatchData {
  44   WatchData()
  45       : id(0), handle_signals(MOJO_HANDLE_SIGNAL_NONE), task_runner(NULL) {}
  46
  47   WatcherID id;
  48   Handle handle;
  49   MojoHandleSignals handle_signals;
  50   base::TimeTicks deadline;
  51   base::Callback<void(MojoResult)> callback;
  52   scoped_refptr<base::SingleThreadTaskRunner> task_runner;
  53 };
  54
  55 // WatcherBackend --------------------------------------------------------------
  56
  57 // WatcherBackend is responsible for managing the requests and interacting with
  58 // MessagePumpMojo. All access (outside of creation/destruction) is done on the
  59 // thread WatcherThreadManager creates.
  60 class WatcherBackend : public MessagePumpMojoHandler {
  61  public:
  62   WatcherBackend();
  63   ~WatcherBackend() override;
  64
  65   void StartWatching(const WatchData& data);
  66
  67   // Cancels a previously scheduled request to start a watch.
  68   void StopWatching(WatcherID watcher_id);
  69
  70  private:
  71   typedef std::map<Handle, WatchData> HandleToWatchDataMap;
  72
  73   // Invoked when a handle needs to be removed and notified.
  74   void RemoveAndNotify(const Handle& handle, MojoResult result);
  75
  76   // Searches through |handle_to_data_| for |watcher_id|. Returns true if found
  77   // and sets |handle| to the Handle. Returns false if not a known id.
  78   bool GetMojoHandleByWatcherID(WatcherID watcher_id, Handle* handle) const;
  79
  80   // MessagePumpMojoHandler overrides:
  81   void OnHandleReady(const Handle& handle) override;
  82   void OnHandleError(const Handle& handle, MojoResult result) override;
  83
  84   // Maps from assigned id to WatchData.
  85   HandleToWatchDataMap handle_to_data_;
  86
  87   DISALLOW_COPY_AND_ASSIGN(WatcherBackend);
  88 };
  89
  90 WatcherBackend::WatcherBackend() {
  91 }
  92
  93 WatcherBackend::~WatcherBackend() {
  94 }
  95
  96 void WatcherBackend::StartWatching(const WatchData& data) {
  97   RemoveAndNotify(data.handle, MOJO_RESULT_CANCELLED);
  98
  99   DCHECK_EQ(0u, handle_to_data_.count(data.handle));
 100
 101   handle_to_data_[data.handle] = data;
 102   MessagePumpMojo::current()->AddHandler(this, data.handle,
 103                                          data.handle_signals,
 104                                          data.deadline);
 105 }
 106
 107 void WatcherBackend::StopWatching(WatcherID watcher_id) {
 108   // Because of the thread hop it is entirely possible to get here and not
 109   // have a valid handle registered for |watcher_id|.
 110   Handle handle;
 111   if (GetMojoHandleByWatcherID(watcher_id, &handle)) {
 112     handle_to_data_.erase(handle);
 113     MessagePumpMojo::current()->RemoveHandler(handle);
 114   }
 115 }
 116
 117 void WatcherBackend::RemoveAndNotify(const Handle& handle,
 118                                      MojoResult result) {
 119   if (handle_to_data_.count(handle) == 0)
 120     return;
 121
 122   const WatchData data(handle_to_data_[handle]);
 123   handle_to_data_.erase(handle);
 124   MessagePumpMojo::current()->RemoveHandler(handle);
 125
 126   data.task_runner->PostTask(FROM_HERE, base::Bind(data.callback, result));
 127 }
 128
 129 bool WatcherBackend::GetMojoHandleByWatcherID(WatcherID watcher_id,
 130                                               Handle* handle) const {
 131   for (HandleToWatchDataMap::const_iterator i = handle_to_data_.begin();
 132        i != handle_to_data_.end(); ++i) {
 133     if (i->second.id == watcher_id) {
 134       *handle = i->second.handle;
 135       return true;
 136     }
 137   }
 138   return false;
 139 }
 140
 141 void WatcherBackend::OnHandleReady(const Handle& handle) {
 142   RemoveAndNotify(handle, MOJO_RESULT_OK);
 143 }
 144
 145 void WatcherBackend::OnHandleError(const Handle& handle, MojoResult result) {
 146   RemoveAndNotify(handle, result);
 147 }
 148
 149 // WatcherThreadManager --------------------------------------------------------
 150
 151 // WatcherThreadManager manages the background thread that listens for handles
 152 // to be ready. All requests are handled by WatcherBackend.
 153 }  // namespace
 154
 155 class WatcherThreadManager {
 156  public:
 157   ~WatcherThreadManager();
 158
 159   // Returns the shared instance.
 160   static WatcherThreadManager* GetInstance();
 161
 162   // Starts watching the requested handle. Returns a unique ID that is used to
 163   // stop watching the handle. When the handle is ready |callback| is notified
 164   // on the thread StartWatching() was invoked on.
 165   // This may be invoked on any thread.
 166   WatcherID StartWatching(const Handle& handle,
 167                           MojoHandleSignals handle_signals,
 168                           base::TimeTicks deadline,
 169                           const base::Callback<void(MojoResult)>& callback);
 170
 171   // Stops watching a handle.
 172   // This may be invoked on any thread.
 173   void StopWatching(WatcherID watcher_id);
 174
 175  private:
 176   enum RequestType {
 177     REQUEST_START,
 178     REQUEST_STOP,
 179   };
 180
 181   // See description of |requests_| for details.
 182   struct RequestData {
 183     RequestData() : type(REQUEST_START), stop_id(0), stop_event(NULL) {}
 184
 185     RequestType type;
 186     WatchData start_data;
 187     WatcherID stop_id;
 188     base::WaitableEvent* stop_event;
 189   };
 190
 191   typedef std::vector<RequestData> Requests;
 192
 193   friend struct DefaultSingletonTraits<WatcherThreadManager>;
 194
 195   WatcherThreadManager();
 196
 197   // Schedules a request on the background thread. See |requests_| for details.
 198   void AddRequest(const RequestData& data);
 199
 200   // Processes requests added to |requests_|. This is invoked on the backend
 201   // thread.
 202   void ProcessRequestsOnBackendThread();
 203
 204   base::Thread thread_;
 205
 206   base::AtomicSequenceNumber watcher_id_generator_;
 207
 208   WatcherBackend backend_;
 209
 210   // Protects |requests_|.
 211   base::Lock lock_;
 212
 213   // Start/Stop result in adding a RequestData to |requests_| (protected by
 214   // |lock_|). When the background thread wakes up it processes the requests.
 215   Requests requests_;
 216
 217   DISALLOW_COPY_AND_ASSIGN(WatcherThreadManager);
 218 };
 219
 220 WatcherThreadManager::~WatcherThreadManager() {
 221   thread_.Stop();
 222 }
 223
 224 WatcherThreadManager* WatcherThreadManager::GetInstance() {
 225   return Singleton<WatcherThreadManager>::get();
 226 }
 227
 228 WatcherID WatcherThreadManager::StartWatching(
 229     const Handle& handle,
 230     MojoHandleSignals handle_signals,
 231     base::TimeTicks deadline,
 232     const base::Callback<void(MojoResult)>& callback) {
 233   RequestData request_data;
 234   request_data.type = REQUEST_START;
 235   request_data.start_data.id = watcher_id_generator_.GetNext();
 236   request_data.start_data.handle = handle;
 237   request_data.start_data.callback = callback;
 238   request_data.start_data.handle_signals = handle_signals;
 239   request_data.start_data.deadline = deadline;
 240   request_data.start_data.task_runner = base::ThreadTaskRunnerHandle::Get();
 241   AddRequest(request_data);
 242   return request_data.start_data.id;
 243 }
 244
 245 void WatcherThreadManager::StopWatching(WatcherID watcher_id) {
 246   // Handle the case of StartWatching() followed by StopWatching() before
 247   // |thread_| woke up.
 248   {
 249     base::AutoLock auto_lock(lock_);
 250     for (Requests::iterator i = requests_.begin(); i != requests_.end(); ++i) {
 251       if (i->type == REQUEST_START && i->start_data.id == watcher_id) {
 252         // Watcher ids are not reused, so if we find it we can stop.
 253         requests_.erase(i);
 254         return;
 255       }
 256     }
 257   }
 258
 259   base::ThreadRestrictions::ScopedAllowWait allow_wait;
 260   base::WaitableEvent event(true, false);
 261   RequestData request_data;
 262   request_data.type = REQUEST_STOP;
 263   request_data.stop_id = watcher_id;
 264   request_data.stop_event = &event;
 265   AddRequest(request_data);
 266
 267   // We need to block until the handle is actually removed.
 268   event.Wait();
 269 }
 270
 271 void WatcherThreadManager::AddRequest(const RequestData& data) {
 272   {
 273     base::AutoLock auto_lock(lock_);
 274     const bool was_empty = requests_.empty();
 275     requests_.push_back(data);
 276     if (!was_empty)
 277       return;
 278   }
 279   // We own |thread_|, so it's safe to use Unretained() here.
 280   thread_.task_runner()->PostTask(
 281       FROM_HERE,
 282       base::Bind(&WatcherThreadManager::ProcessRequestsOnBackendThread,
 283                  base::Unretained(this)));
 284 }
 285
 286 void WatcherThreadManager::ProcessRequestsOnBackendThread() {
 287   DCHECK_EQ(thread_.message_loop(), base::MessageLoop::current());
 288
 289   Requests requests;
 290   {
 291     base::AutoLock auto_lock(lock_);
 292     requests_.swap(requests);
 293   }
 294   for (size_t i = 0; i < requests.size(); ++i) {
 295     if (requests[i].type == REQUEST_START) {
 296       backend_.StartWatching(requests[i].start_data);
 297     } else {
 298       backend_.StopWatching(requests[i].stop_id);
 299       requests[i].stop_event->Signal();
 300     }
 301   }
 302 }
 303
 304 WatcherThreadManager::WatcherThreadManager()
 305     : thread_(kWatcherThreadName) {
 306   base::Thread::Options thread_options;
 307   thread_options.message_pump_factory = base::Bind(&MessagePumpMojo::Create);
 308   thread_.StartWithOptions(thread_options);
 309 }
 310
 311 // HandleWatcher::StateBase and subclasses -------------------------------------
 312
 313 // The base class of HandleWatcher's state. Owns the user's callback and
 314 // monitors the current thread's MessageLoop to know when to force the callback
 315 // to run (with an error) even though the pipe hasn't been signaled yet.
 316 class HandleWatcher::StateBase : public base::MessageLoop::DestructionObserver {
 317  public:
 318   StateBase(HandleWatcher* watcher,
 319             const base::Callback<void(MojoResult)>& callback)
 320       : watcher_(watcher),
 321         callback_(callback),
 322         got_ready_(false) {
 323     base::MessageLoop::current()->AddDestructionObserver(this);
 324   }
 325
 326   ~StateBase() override {
 327     base::MessageLoop::current()->RemoveDestructionObserver(this);
 328   }
 329
 330  protected:
 331   void NotifyHandleReady(MojoResult result) {
 332     got_ready_ = true;
 333     NotifyAndDestroy(result);
 334   }
 335
 336   bool got_ready() const { return got_ready_; }
 337
 338  private:
 339   void WillDestroyCurrentMessageLoop() override {
 340     // The current thread is exiting. Simulate a watch error.
 341     NotifyAndDestroy(MOJO_RESULT_ABORTED);
 342   }
 343
 344   void NotifyAndDestroy(MojoResult result) {
 345     base::Callback<void(MojoResult)> callback = callback_;
 346     watcher_->Stop();  // Destroys |this|.
 347
 348     callback.Run(result);
 349   }
 350
 351   HandleWatcher* watcher_;
 352   base::Callback<void(MojoResult)> callback_;
 353
 354   // Have we been notified that the handle is ready?
 355   bool got_ready_;
 356
 357   DISALLOW_COPY_AND_ASSIGN(StateBase);
 358 };
 359
 360 // If the thread on which HandleWatcher is used runs MessagePumpMojo,
 361 // SameThreadWatchingState is used to directly watch the handle on the same
 362 // thread.
 363 class HandleWatcher::SameThreadWatchingState : public StateBase,
 364                                                public MessagePumpMojoHandler {
 365  public:
 366   SameThreadWatchingState(HandleWatcher* watcher,
 367                           const Handle& handle,
 368                           MojoHandleSignals handle_signals,
 369                           MojoDeadline deadline,
 370                           const base::Callback<void(MojoResult)>& callback)
 371       : StateBase(watcher, callback),
 372         handle_(handle) {
 373     DCHECK(MessagePumpMojo::IsCurrent());
 374
 375     MessagePumpMojo::current()->AddHandler(
 376         this, handle, handle_signals, MojoDeadlineToTimeTicks(deadline));
 377   }
 378
 379   ~SameThreadWatchingState() override {
 380     if (!got_ready())
 381       MessagePumpMojo::current()->RemoveHandler(handle_);
 382   }
 383
 384  private:
 385   // MessagePumpMojoHandler overrides:
 386   void OnHandleReady(const Handle& handle) override {
 387     StopWatchingAndNotifyReady(handle, MOJO_RESULT_OK);
 388   }
 389
 390   void OnHandleError(const Handle& handle, MojoResult result) override {
 391     StopWatchingAndNotifyReady(handle, result);
 392   }
 393
 394   void StopWatchingAndNotifyReady(const Handle& handle, MojoResult result) {
 395     DCHECK_EQ(handle.value(), handle_.value());
 396     MessagePumpMojo::current()->RemoveHandler(handle_);
 397     NotifyHandleReady(result);
 398   }
 399
 400   Handle handle_;
 401
 402   DISALLOW_COPY_AND_ASSIGN(SameThreadWatchingState);
 403 };
 404
 405 // If the thread on which HandleWatcher is used runs a message pump different
 406 // from MessagePumpMojo, SecondaryThreadWatchingState is used to watch the
 407 // handle on the handle watcher thread.
 408 class HandleWatcher::SecondaryThreadWatchingState : public StateBase {
 409  public:
 410   SecondaryThreadWatchingState(HandleWatcher* watcher,
 411                                const Handle& handle,
 412                                MojoHandleSignals handle_signals,
 413                                MojoDeadline deadline,
 414                                const base::Callback<void(MojoResult)>& callback)
 415       : StateBase(watcher, callback),
 416         weak_factory_(this) {
 417     watcher_id_ = WatcherThreadManager::GetInstance()->StartWatching(
 418         handle,
 419         handle_signals,
 420         MojoDeadlineToTimeTicks(deadline),
 421         base::Bind(&SecondaryThreadWatchingState::NotifyHandleReady,
 422                    weak_factory_.GetWeakPtr()));
 423   }
 424
 425   ~SecondaryThreadWatchingState() override {
 426     // If we've been notified the handle is ready (|got_ready()| is true) then
 427     // the watch has been implicitly removed by
 428     // WatcherThreadManager/MessagePumpMojo and we don't have to call
 429     // StopWatching(). To do so would needlessly entail posting a task and
 430     // blocking until the background thread services it.
 431     if (!got_ready())
 432       WatcherThreadManager::GetInstance()->StopWatching(watcher_id_);
 433   }
 434
 435  private:
 436   WatcherID watcher_id_;
 437
 438   // Used to weakly bind |this| to the WatcherThreadManager.
 439   base::WeakPtrFactory<SecondaryThreadWatchingState> weak_factory_;
 440
 441   DISALLOW_COPY_AND_ASSIGN(SecondaryThreadWatchingState);
 442 };
 443
 444 // HandleWatcher ---------------------------------------------------------------
 445
 446 HandleWatcher::HandleWatcher() {
 447 }
 448
 449 HandleWatcher::~HandleWatcher() {
 450 }
 451
 452 void HandleWatcher::Start(const Handle& handle,
 453                           MojoHandleSignals handle_signals,
 454                           MojoDeadline deadline,
 455                           const base::Callback<void(MojoResult)>& callback) {
 456   DCHECK(handle.is_valid());
 457   DCHECK_NE(MOJO_HANDLE_SIGNAL_NONE, handle_signals);
 458
 459   // Need to clear the state before creating a new one.
 460   state_.reset();
 461   if (MessagePumpMojo::IsCurrent()) {
 462     state_.reset(new SameThreadWatchingState(
 463         this, handle, handle_signals, deadline, callback));
 464   } else {
 465     state_.reset(new SecondaryThreadWatchingState(
 466         this, handle, handle_signals, deadline, callback));
 467   }
 468 }
 469
 470 void HandleWatcher::Stop() {
 471   state_.reset();
 472 }
 473
 474 }  // namespace common
 475 }  // namespace mojo