15821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Copyright (c) 2011 The Chromium Authors. All rights reserved. 25821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Use of this source code is governed by a BSD-style license that can be 35821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// found in the LICENSE file. 45821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 55821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/lazy_instance.h" 65821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 75821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/at_exit.h" 85821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/atomicops.h" 95821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/basictypes.h" 105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/threading/platform_thread.h" 115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/third_party/dynamic_annotations/dynamic_annotations.h" 125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)namespace base { 145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)namespace internal { 155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// TODO(joth): This function could be shared with Singleton, in place of its 175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// WaitForInstance() call. 185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)bool NeedsLazyInstance(subtle::AtomicWord* state) { 195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Try to create the instance, if we're the first, will go from 0 to 205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // kLazyInstanceStateCreating, otherwise we've already been beaten here. 215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // The memory access has no memory ordering as state 0 and 225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // kLazyInstanceStateCreating have no associated data (memory barriers are 235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // all about ordering of memory accesses to *associated* data). 245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (subtle::NoBarrier_CompareAndSwap(state, 0, 255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) kLazyInstanceStateCreating) == 0) 265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Caller must create instance 275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return true; 285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // It's either in the process of being created, or already created. Spin. 305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // The load has acquire memory ordering as a thread which sees 315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // state_ == STATE_CREATED needs to acquire visibility over 325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // the associated data (buf_). Pairing Release_Store is in 335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // CompleteLazyInstance(). 345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) while (subtle::Acquire_Load(state) == kLazyInstanceStateCreating) { 355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) PlatformThread::YieldCurrentThread(); 365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Someone else created the instance. 385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return false; 395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} 405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)void CompleteLazyInstance(subtle::AtomicWord* state, 425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) subtle::AtomicWord new_instance, 435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void* lazy_instance, 445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) void (*dtor)(void*)) { 455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // See the comment to the corresponding HAPPENS_AFTER in Pointer(). 465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) ANNOTATE_HAPPENS_BEFORE(state); 475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Instance is created, go from CREATING to CREATED. 495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Releases visibility over private_buf_ to readers. Pairing Acquire_Load's 505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // are in NeedsInstance() and Pointer(). 515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) subtle::Release_Store(state, new_instance); 525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 535821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Make sure that the lazily instantiated object will get destroyed at exit. 545821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (dtor) 555821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) AtExitManager::RegisterCallback(dtor, lazy_instance); 565821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} 575821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 585821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} // namespace internal 595821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} // namespace base 60