114 lines
3.2 KiB
C++
114 lines
3.2 KiB
C++
// Copyright (C) 2014 The Android Open Source Project
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "emugl/common/condition_variable.h"
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#include "emugl/common/lazy_instance.h"
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#include "emugl/common/mutex.h"
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#include "emugl/common/pod_vector.h"
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// Technical note: this is loosely based on the Chromium implementation
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// of ConditionVariable. This version works on Windows XP and above and
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// doesn't try to use Vista's CONDITION_VARIABLE types.
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namespace emugl {
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namespace {
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// Helper class which implements a free list of event handles.
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class WaitEventStorage {
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public:
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WaitEventStorage() : mFreeHandles(), mLock() {}
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~WaitEventStorage() {
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for (size_t n = 0; n < mFreeHandles.size(); ++n) {
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CloseHandle(mFreeHandles[n]);
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}
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}
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HANDLE alloc() {
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HANDLE handle;
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mLock.lock();
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size_t size = mFreeHandles.size();
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if (size > 0) {
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handle = mFreeHandles[size - 1U];
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mFreeHandles.remove(size - 1U);
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} else {
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handle = CreateEvent(NULL, TRUE, FALSE, NULL);
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}
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mLock.unlock();
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return handle;
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}
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void free(HANDLE h) {
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mLock.lock();
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ResetEvent(h);
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mFreeHandles.push_back(h);
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mLock.unlock();
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}
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private:
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PodVector<HANDLE> mFreeHandles;
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Mutex mLock;
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};
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LazyInstance<WaitEventStorage> sWaitEvents = LAZY_INSTANCE_INIT;
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} // namespace
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ConditionVariable::ConditionVariable() : mWaiters(), mLock() {}
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ConditionVariable::~ConditionVariable() {
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mLock.lock();
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for (size_t n = 0; n < mWaiters.size(); ++n) {
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CloseHandle(mWaiters[n]);
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}
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mWaiters.resize(0U);
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mLock.unlock();
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}
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void ConditionVariable::wait(Mutex* userLock) {
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// Grab new waiter event handle.
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mLock.lock();
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HANDLE handle = sWaitEvents->alloc();
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mWaiters.push_back(handle);
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mLock.unlock();
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// Unlock user lock then wait for event.
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userLock->unlock();
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WaitForSingleObject(handle, INFINITE);
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// NOTE: The handle has been removed from mWaiters here,
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// see signal() below. Close/recycle the event.
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sWaitEvents->free(handle);
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userLock->lock();
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}
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void ConditionVariable::signal() {
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mLock.lock();
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size_t size = mWaiters.size();
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if (size > 0U) {
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// NOTE: This wakes up the thread that went to sleep most
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// recently (LIFO) for performance reason. For better
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// fairness, using (FIFO) would be appropriate.
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HANDLE handle = mWaiters[size - 1U];
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mWaiters.remove(size - 1U);
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SetEvent(handle);
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// NOTE: The handle will be closed/recycled by the waiter.
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} else {
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// Nothing to signal.
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}
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mLock.unlock();
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}
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} // namespace emugl
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