1 // Copyright (c) 2012 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 "base/message_loop/message_pump_win.h" 6 7 #include <math.h> 8 9 #include "base/debug/trace_event.h" 10 #include "base/message_loop/message_loop.h" 11 #include "base/metrics/histogram.h" 12 #include "base/process/memory.h" 13 #include "base/strings/stringprintf.h" 14 #include "base/win/wrapped_window_proc.h" 15 16 namespace base { 17 18 namespace { 19 20 enum MessageLoopProblems { 21 MESSAGE_POST_ERROR, 22 COMPLETION_POST_ERROR, 23 SET_TIMER_ERROR, 24 MESSAGE_LOOP_PROBLEM_MAX, 25 }; 26 27 } // namespace 28 29 static const wchar_t kWndClassFormat[] = L"Chrome_MessagePumpWindow_%p"; 30 31 // Message sent to get an additional time slice for pumping (processing) another 32 // task (a series of such messages creates a continuous task pump). 33 static const int kMsgHaveWork = WM_USER + 1; 34 35 //----------------------------------------------------------------------------- 36 // MessagePumpWin public: 37 38 void MessagePumpWin::RunWithDispatcher( 39 Delegate* delegate, MessagePumpDispatcher* dispatcher) { 40 RunState s; 41 s.delegate = delegate; 42 s.dispatcher = dispatcher; 43 s.should_quit = false; 44 s.run_depth = state_ ? state_->run_depth + 1 : 1; 45 46 RunState* previous_state = state_; 47 state_ = &s; 48 49 DoRunLoop(); 50 51 state_ = previous_state; 52 } 53 54 void MessagePumpWin::Quit() { 55 DCHECK(state_); 56 state_->should_quit = true; 57 } 58 59 //----------------------------------------------------------------------------- 60 // MessagePumpWin protected: 61 62 int MessagePumpWin::GetCurrentDelay() const { 63 if (delayed_work_time_.is_null()) 64 return -1; 65 66 // Be careful here. TimeDelta has a precision of microseconds, but we want a 67 // value in milliseconds. If there are 5.5ms left, should the delay be 5 or 68 // 6? It should be 6 to avoid executing delayed work too early. 69 double timeout = 70 ceil((delayed_work_time_ - TimeTicks::Now()).InMillisecondsF()); 71 72 // If this value is negative, then we need to run delayed work soon. 73 int delay = static_cast<int>(timeout); 74 if (delay < 0) 75 delay = 0; 76 77 return delay; 78 } 79 80 //----------------------------------------------------------------------------- 81 // MessagePumpForUI public: 82 83 MessagePumpForUI::MessagePumpForUI() 84 : atom_(0) { 85 InitMessageWnd(); 86 } 87 88 MessagePumpForUI::~MessagePumpForUI() { 89 DestroyWindow(message_hwnd_); 90 UnregisterClass(MAKEINTATOM(atom_), 91 GetModuleFromAddress(&WndProcThunk)); 92 } 93 94 void MessagePumpForUI::ScheduleWork() { 95 if (InterlockedExchange(&have_work_, 1)) 96 return; // Someone else continued the pumping. 97 98 // Make sure the MessagePump does some work for us. 99 BOOL ret = PostMessage(message_hwnd_, kMsgHaveWork, 100 reinterpret_cast<WPARAM>(this), 0); 101 if (ret) 102 return; // There was room in the Window Message queue. 103 104 // We have failed to insert a have-work message, so there is a chance that we 105 // will starve tasks/timers while sitting in a nested message loop. Nested 106 // loops only look at Windows Message queues, and don't look at *our* task 107 // queues, etc., so we might not get a time slice in such. :-( 108 // We could abort here, but the fear is that this failure mode is plausibly 109 // common (queue is full, of about 2000 messages), so we'll do a near-graceful 110 // recovery. Nested loops are pretty transient (we think), so this will 111 // probably be recoverable. 112 InterlockedExchange(&have_work_, 0); // Clarify that we didn't really insert. 113 UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem", MESSAGE_POST_ERROR, 114 MESSAGE_LOOP_PROBLEM_MAX); 115 } 116 117 void MessagePumpForUI::ScheduleDelayedWork(const TimeTicks& delayed_work_time) { 118 // 119 // We would *like* to provide high resolution timers. Windows timers using 120 // SetTimer() have a 10ms granularity. We have to use WM_TIMER as a wakeup 121 // mechanism because the application can enter modal windows loops where it 122 // is not running our MessageLoop; the only way to have our timers fire in 123 // these cases is to post messages there. 124 // 125 // To provide sub-10ms timers, we process timers directly from our run loop. 126 // For the common case, timers will be processed there as the run loop does 127 // its normal work. However, we *also* set the system timer so that WM_TIMER 128 // events fire. This mops up the case of timers not being able to work in 129 // modal message loops. It is possible for the SetTimer to pop and have no 130 // pending timers, because they could have already been processed by the 131 // run loop itself. 132 // 133 // We use a single SetTimer corresponding to the timer that will expire 134 // soonest. As new timers are created and destroyed, we update SetTimer. 135 // Getting a spurrious SetTimer event firing is benign, as we'll just be 136 // processing an empty timer queue. 137 // 138 delayed_work_time_ = delayed_work_time; 139 140 int delay_msec = GetCurrentDelay(); 141 DCHECK_GE(delay_msec, 0); 142 if (delay_msec < USER_TIMER_MINIMUM) 143 delay_msec = USER_TIMER_MINIMUM; 144 145 // Create a WM_TIMER event that will wake us up to check for any pending 146 // timers (in case we are running within a nested, external sub-pump). 147 BOOL ret = SetTimer(message_hwnd_, reinterpret_cast<UINT_PTR>(this), 148 delay_msec, NULL); 149 if (ret) 150 return; 151 // If we can't set timers, we are in big trouble... but cross our fingers for 152 // now. 153 // TODO(jar): If we don't see this error, use a CHECK() here instead. 154 UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem", SET_TIMER_ERROR, 155 MESSAGE_LOOP_PROBLEM_MAX); 156 } 157 158 //----------------------------------------------------------------------------- 159 // MessagePumpForUI private: 160 161 // static 162 LRESULT CALLBACK MessagePumpForUI::WndProcThunk( 163 HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam) { 164 switch (message) { 165 case kMsgHaveWork: 166 reinterpret_cast<MessagePumpForUI*>(wparam)->HandleWorkMessage(); 167 break; 168 case WM_TIMER: 169 reinterpret_cast<MessagePumpForUI*>(wparam)->HandleTimerMessage(); 170 break; 171 } 172 return DefWindowProc(hwnd, message, wparam, lparam); 173 } 174 175 void MessagePumpForUI::DoRunLoop() { 176 // IF this was just a simple PeekMessage() loop (servicing all possible work 177 // queues), then Windows would try to achieve the following order according 178 // to MSDN documentation about PeekMessage with no filter): 179 // * Sent messages 180 // * Posted messages 181 // * Sent messages (again) 182 // * WM_PAINT messages 183 // * WM_TIMER messages 184 // 185 // Summary: none of the above classes is starved, and sent messages has twice 186 // the chance of being processed (i.e., reduced service time). 187 188 for (;;) { 189 // If we do any work, we may create more messages etc., and more work may 190 // possibly be waiting in another task group. When we (for example) 191 // ProcessNextWindowsMessage(), there is a good chance there are still more 192 // messages waiting. On the other hand, when any of these methods return 193 // having done no work, then it is pretty unlikely that calling them again 194 // quickly will find any work to do. Finally, if they all say they had no 195 // work, then it is a good time to consider sleeping (waiting) for more 196 // work. 197 198 bool more_work_is_plausible = ProcessNextWindowsMessage(); 199 if (state_->should_quit) 200 break; 201 202 more_work_is_plausible |= state_->delegate->DoWork(); 203 if (state_->should_quit) 204 break; 205 206 more_work_is_plausible |= 207 state_->delegate->DoDelayedWork(&delayed_work_time_); 208 // If we did not process any delayed work, then we can assume that our 209 // existing WM_TIMER if any will fire when delayed work should run. We 210 // don't want to disturb that timer if it is already in flight. However, 211 // if we did do all remaining delayed work, then lets kill the WM_TIMER. 212 if (more_work_is_plausible && delayed_work_time_.is_null()) 213 KillTimer(message_hwnd_, reinterpret_cast<UINT_PTR>(this)); 214 if (state_->should_quit) 215 break; 216 217 if (more_work_is_plausible) 218 continue; 219 220 more_work_is_plausible = state_->delegate->DoIdleWork(); 221 if (state_->should_quit) 222 break; 223 224 if (more_work_is_plausible) 225 continue; 226 227 WaitForWork(); // Wait (sleep) until we have work to do again. 228 } 229 } 230 231 void MessagePumpForUI::InitMessageWnd() { 232 // Generate a unique window class name. 233 string16 class_name = StringPrintf(kWndClassFormat, this); 234 235 HINSTANCE instance = GetModuleFromAddress(&WndProcThunk); 236 WNDCLASSEX wc = {0}; 237 wc.cbSize = sizeof(wc); 238 wc.lpfnWndProc = base::win::WrappedWindowProc<WndProcThunk>; 239 wc.hInstance = instance; 240 wc.lpszClassName = class_name.c_str(); 241 atom_ = RegisterClassEx(&wc); 242 DCHECK(atom_); 243 244 message_hwnd_ = CreateWindow(MAKEINTATOM(atom_), 0, 0, 0, 0, 0, 0, 245 HWND_MESSAGE, 0, instance, 0); 246 DCHECK(message_hwnd_); 247 } 248 249 void MessagePumpForUI::WaitForWork() { 250 // Wait until a message is available, up to the time needed by the timer 251 // manager to fire the next set of timers. 252 int delay = GetCurrentDelay(); 253 if (delay < 0) // Negative value means no timers waiting. 254 delay = INFINITE; 255 256 DWORD result; 257 result = MsgWaitForMultipleObjectsEx(0, NULL, delay, QS_ALLINPUT, 258 MWMO_INPUTAVAILABLE); 259 260 if (WAIT_OBJECT_0 == result) { 261 // A WM_* message is available. 262 // If a parent child relationship exists between windows across threads 263 // then their thread inputs are implicitly attached. 264 // This causes the MsgWaitForMultipleObjectsEx API to return indicating 265 // that messages are ready for processing (Specifically, mouse messages 266 // intended for the child window may appear if the child window has 267 // capture). 268 // The subsequent PeekMessages call may fail to return any messages thus 269 // causing us to enter a tight loop at times. 270 // The WaitMessage call below is a workaround to give the child window 271 // some time to process its input messages. 272 MSG msg = {0}; 273 DWORD queue_status = GetQueueStatus(QS_MOUSE); 274 if (HIWORD(queue_status) & QS_MOUSE && 275 !PeekMessage(&msg, NULL, WM_MOUSEFIRST, WM_MOUSELAST, PM_NOREMOVE)) { 276 WaitMessage(); 277 } 278 return; 279 } 280 281 DCHECK_NE(WAIT_FAILED, result) << GetLastError(); 282 } 283 284 void MessagePumpForUI::HandleWorkMessage() { 285 // If we are being called outside of the context of Run, then don't try to do 286 // any work. This could correspond to a MessageBox call or something of that 287 // sort. 288 if (!state_) { 289 // Since we handled a kMsgHaveWork message, we must still update this flag. 290 InterlockedExchange(&have_work_, 0); 291 return; 292 } 293 294 // Let whatever would have run had we not been putting messages in the queue 295 // run now. This is an attempt to make our dummy message not starve other 296 // messages that may be in the Windows message queue. 297 ProcessPumpReplacementMessage(); 298 299 // Now give the delegate a chance to do some work. He'll let us know if he 300 // needs to do more work. 301 if (state_->delegate->DoWork()) 302 ScheduleWork(); 303 } 304 305 void MessagePumpForUI::HandleTimerMessage() { 306 KillTimer(message_hwnd_, reinterpret_cast<UINT_PTR>(this)); 307 308 // If we are being called outside of the context of Run, then don't do 309 // anything. This could correspond to a MessageBox call or something of 310 // that sort. 311 if (!state_) 312 return; 313 314 state_->delegate->DoDelayedWork(&delayed_work_time_); 315 if (!delayed_work_time_.is_null()) { 316 // A bit gratuitous to set delayed_work_time_ again, but oh well. 317 ScheduleDelayedWork(delayed_work_time_); 318 } 319 } 320 321 bool MessagePumpForUI::ProcessNextWindowsMessage() { 322 // If there are sent messages in the queue then PeekMessage internally 323 // dispatches the message and returns false. We return true in this 324 // case to ensure that the message loop peeks again instead of calling 325 // MsgWaitForMultipleObjectsEx again. 326 bool sent_messages_in_queue = false; 327 DWORD queue_status = GetQueueStatus(QS_SENDMESSAGE); 328 if (HIWORD(queue_status) & QS_SENDMESSAGE) 329 sent_messages_in_queue = true; 330 331 MSG msg; 332 if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE) != FALSE) 333 return ProcessMessageHelper(msg); 334 335 return sent_messages_in_queue; 336 } 337 338 bool MessagePumpForUI::ProcessMessageHelper(const MSG& msg) { 339 TRACE_EVENT1("base", "MessagePumpForUI::ProcessMessageHelper", 340 "message", msg.message); 341 if (WM_QUIT == msg.message) { 342 // Repost the QUIT message so that it will be retrieved by the primary 343 // GetMessage() loop. 344 state_->should_quit = true; 345 PostQuitMessage(static_cast<int>(msg.wParam)); 346 return false; 347 } 348 349 // While running our main message pump, we discard kMsgHaveWork messages. 350 if (msg.message == kMsgHaveWork && msg.hwnd == message_hwnd_) 351 return ProcessPumpReplacementMessage(); 352 353 if (CallMsgFilter(const_cast<MSG*>(&msg), kMessageFilterCode)) 354 return true; 355 356 uint32_t action = MessagePumpDispatcher::POST_DISPATCH_PERFORM_DEFAULT; 357 if (state_->dispatcher) 358 action = state_->dispatcher->Dispatch(msg); 359 if (action & MessagePumpDispatcher::POST_DISPATCH_QUIT_LOOP) 360 state_->should_quit = true; 361 if (action & MessagePumpDispatcher::POST_DISPATCH_PERFORM_DEFAULT) { 362 TranslateMessage(&msg); 363 DispatchMessage(&msg); 364 } 365 366 return true; 367 } 368 369 bool MessagePumpForUI::ProcessPumpReplacementMessage() { 370 // When we encounter a kMsgHaveWork message, this method is called to peek 371 // and process a replacement message, such as a WM_PAINT or WM_TIMER. The 372 // goal is to make the kMsgHaveWork as non-intrusive as possible, even though 373 // a continuous stream of such messages are posted. This method carefully 374 // peeks a message while there is no chance for a kMsgHaveWork to be pending, 375 // then resets the have_work_ flag (allowing a replacement kMsgHaveWork to 376 // possibly be posted), and finally dispatches that peeked replacement. Note 377 // that the re-post of kMsgHaveWork may be asynchronous to this thread!! 378 379 bool have_message = false; 380 MSG msg; 381 // We should not process all window messages if we are in the context of an 382 // OS modal loop, i.e. in the context of a windows API call like MessageBox. 383 // This is to ensure that these messages are peeked out by the OS modal loop. 384 if (MessageLoop::current()->os_modal_loop()) { 385 // We only peek out WM_PAINT and WM_TIMER here for reasons mentioned above. 386 have_message = PeekMessage(&msg, NULL, WM_PAINT, WM_PAINT, PM_REMOVE) || 387 PeekMessage(&msg, NULL, WM_TIMER, WM_TIMER, PM_REMOVE); 388 } else { 389 have_message = PeekMessage(&msg, NULL, 0, 0, PM_REMOVE) != FALSE; 390 } 391 392 DCHECK(!have_message || kMsgHaveWork != msg.message || 393 msg.hwnd != message_hwnd_); 394 395 // Since we discarded a kMsgHaveWork message, we must update the flag. 396 int old_have_work = InterlockedExchange(&have_work_, 0); 397 DCHECK(old_have_work); 398 399 // We don't need a special time slice if we didn't have_message to process. 400 if (!have_message) 401 return false; 402 403 // Guarantee we'll get another time slice in the case where we go into native 404 // windows code. This ScheduleWork() may hurt performance a tiny bit when 405 // tasks appear very infrequently, but when the event queue is busy, the 406 // kMsgHaveWork events get (percentage wise) rarer and rarer. 407 ScheduleWork(); 408 return ProcessMessageHelper(msg); 409 } 410 411 //----------------------------------------------------------------------------- 412 // MessagePumpForIO public: 413 414 MessagePumpForIO::MessagePumpForIO() { 415 port_.Set(CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, NULL, 1)); 416 DCHECK(port_.IsValid()); 417 } 418 419 void MessagePumpForIO::ScheduleWork() { 420 if (InterlockedExchange(&have_work_, 1)) 421 return; // Someone else continued the pumping. 422 423 // Make sure the MessagePump does some work for us. 424 BOOL ret = PostQueuedCompletionStatus(port_.Get(), 0, 425 reinterpret_cast<ULONG_PTR>(this), 426 reinterpret_cast<OVERLAPPED*>(this)); 427 if (ret) 428 return; // Post worked perfectly. 429 430 // See comment in MessagePumpForUI::ScheduleWork() for this error recovery. 431 InterlockedExchange(&have_work_, 0); // Clarify that we didn't succeed. 432 UMA_HISTOGRAM_ENUMERATION("Chrome.MessageLoopProblem", COMPLETION_POST_ERROR, 433 MESSAGE_LOOP_PROBLEM_MAX); 434 } 435 436 void MessagePumpForIO::ScheduleDelayedWork(const TimeTicks& delayed_work_time) { 437 // We know that we can't be blocked right now since this method can only be 438 // called on the same thread as Run, so we only need to update our record of 439 // how long to sleep when we do sleep. 440 delayed_work_time_ = delayed_work_time; 441 } 442 443 void MessagePumpForIO::RegisterIOHandler(HANDLE file_handle, 444 IOHandler* handler) { 445 ULONG_PTR key = HandlerToKey(handler, true); 446 HANDLE port = CreateIoCompletionPort(file_handle, port_.Get(), key, 1); 447 DPCHECK(port); 448 } 449 450 bool MessagePumpForIO::RegisterJobObject(HANDLE job_handle, 451 IOHandler* handler) { 452 // Job object notifications use the OVERLAPPED pointer to carry the message 453 // data. Mark the completion key correspondingly, so we will not try to 454 // convert OVERLAPPED* to IOContext*. 455 ULONG_PTR key = HandlerToKey(handler, false); 456 JOBOBJECT_ASSOCIATE_COMPLETION_PORT info; 457 info.CompletionKey = reinterpret_cast<void*>(key); 458 info.CompletionPort = port_.Get(); 459 return SetInformationJobObject(job_handle, 460 JobObjectAssociateCompletionPortInformation, 461 &info, 462 sizeof(info)) != FALSE; 463 } 464 465 //----------------------------------------------------------------------------- 466 // MessagePumpForIO private: 467 468 void MessagePumpForIO::DoRunLoop() { 469 for (;;) { 470 // If we do any work, we may create more messages etc., and more work may 471 // possibly be waiting in another task group. When we (for example) 472 // WaitForIOCompletion(), there is a good chance there are still more 473 // messages waiting. On the other hand, when any of these methods return 474 // having done no work, then it is pretty unlikely that calling them 475 // again quickly will find any work to do. Finally, if they all say they 476 // had no work, then it is a good time to consider sleeping (waiting) for 477 // more work. 478 479 bool more_work_is_plausible = state_->delegate->DoWork(); 480 if (state_->should_quit) 481 break; 482 483 more_work_is_plausible |= WaitForIOCompletion(0, NULL); 484 if (state_->should_quit) 485 break; 486 487 more_work_is_plausible |= 488 state_->delegate->DoDelayedWork(&delayed_work_time_); 489 if (state_->should_quit) 490 break; 491 492 if (more_work_is_plausible) 493 continue; 494 495 more_work_is_plausible = state_->delegate->DoIdleWork(); 496 if (state_->should_quit) 497 break; 498 499 if (more_work_is_plausible) 500 continue; 501 502 WaitForWork(); // Wait (sleep) until we have work to do again. 503 } 504 } 505 506 // Wait until IO completes, up to the time needed by the timer manager to fire 507 // the next set of timers. 508 void MessagePumpForIO::WaitForWork() { 509 // We do not support nested IO message loops. This is to avoid messy 510 // recursion problems. 511 DCHECK_EQ(1, state_->run_depth) << "Cannot nest an IO message loop!"; 512 513 int timeout = GetCurrentDelay(); 514 if (timeout < 0) // Negative value means no timers waiting. 515 timeout = INFINITE; 516 517 WaitForIOCompletion(timeout, NULL); 518 } 519 520 bool MessagePumpForIO::WaitForIOCompletion(DWORD timeout, IOHandler* filter) { 521 IOItem item; 522 if (completed_io_.empty() || !MatchCompletedIOItem(filter, &item)) { 523 // We have to ask the system for another IO completion. 524 if (!GetIOItem(timeout, &item)) 525 return false; 526 527 if (ProcessInternalIOItem(item)) 528 return true; 529 } 530 531 // If |item.has_valid_io_context| is false then |item.context| does not point 532 // to a context structure, and so should not be dereferenced, although it may 533 // still hold valid non-pointer data. 534 if (!item.has_valid_io_context || item.context->handler) { 535 if (filter && item.handler != filter) { 536 // Save this item for later 537 completed_io_.push_back(item); 538 } else { 539 DCHECK(!item.has_valid_io_context || 540 (item.context->handler == item.handler)); 541 WillProcessIOEvent(); 542 item.handler->OnIOCompleted(item.context, item.bytes_transfered, 543 item.error); 544 DidProcessIOEvent(); 545 } 546 } else { 547 // The handler must be gone by now, just cleanup the mess. 548 delete item.context; 549 } 550 return true; 551 } 552 553 // Asks the OS for another IO completion result. 554 bool MessagePumpForIO::GetIOItem(DWORD timeout, IOItem* item) { 555 memset(item, 0, sizeof(*item)); 556 ULONG_PTR key = NULL; 557 OVERLAPPED* overlapped = NULL; 558 if (!GetQueuedCompletionStatus(port_.Get(), &item->bytes_transfered, &key, 559 &overlapped, timeout)) { 560 if (!overlapped) 561 return false; // Nothing in the queue. 562 item->error = GetLastError(); 563 item->bytes_transfered = 0; 564 } 565 566 item->handler = KeyToHandler(key, &item->has_valid_io_context); 567 item->context = reinterpret_cast<IOContext*>(overlapped); 568 return true; 569 } 570 571 bool MessagePumpForIO::ProcessInternalIOItem(const IOItem& item) { 572 if (this == reinterpret_cast<MessagePumpForIO*>(item.context) && 573 this == reinterpret_cast<MessagePumpForIO*>(item.handler)) { 574 // This is our internal completion. 575 DCHECK(!item.bytes_transfered); 576 InterlockedExchange(&have_work_, 0); 577 return true; 578 } 579 return false; 580 } 581 582 // Returns a completion item that was previously received. 583 bool MessagePumpForIO::MatchCompletedIOItem(IOHandler* filter, IOItem* item) { 584 DCHECK(!completed_io_.empty()); 585 for (std::list<IOItem>::iterator it = completed_io_.begin(); 586 it != completed_io_.end(); ++it) { 587 if (!filter || it->handler == filter) { 588 *item = *it; 589 completed_io_.erase(it); 590 return true; 591 } 592 } 593 return false; 594 } 595 596 void MessagePumpForIO::AddIOObserver(IOObserver *obs) { 597 io_observers_.AddObserver(obs); 598 } 599 600 void MessagePumpForIO::RemoveIOObserver(IOObserver *obs) { 601 io_observers_.RemoveObserver(obs); 602 } 603 604 void MessagePumpForIO::WillProcessIOEvent() { 605 FOR_EACH_OBSERVER(IOObserver, io_observers_, WillProcessIOEvent()); 606 } 607 608 void MessagePumpForIO::DidProcessIOEvent() { 609 FOR_EACH_OBSERVER(IOObserver, io_observers_, DidProcessIOEvent()); 610 } 611 612 // static 613 ULONG_PTR MessagePumpForIO::HandlerToKey(IOHandler* handler, 614 bool has_valid_io_context) { 615 ULONG_PTR key = reinterpret_cast<ULONG_PTR>(handler); 616 617 // |IOHandler| is at least pointer-size aligned, so the lowest two bits are 618 // always cleared. We use the lowest bit to distinguish completion keys with 619 // and without the associated |IOContext|. 620 DCHECK((key & 1) == 0); 621 622 // Mark the completion key as context-less. 623 if (!has_valid_io_context) 624 key = key | 1; 625 return key; 626 } 627 628 // static 629 MessagePumpForIO::IOHandler* MessagePumpForIO::KeyToHandler( 630 ULONG_PTR key, 631 bool* has_valid_io_context) { 632 *has_valid_io_context = ((key & 1) == 0); 633 return reinterpret_cast<IOHandler*>(key & ~static_cast<ULONG_PTR>(1)); 634 } 635 636 } // namespace base 637