b154c42c39
The existing code worked in practice, but wasn't quite correct in
theory and relied on implementation details of other code. It's still
somewhat unusual and subtle, but now is correct-in-theory (I believe)
and a little better documented.
Bug: 16044767
Change-Id: I22b01d6640f0b7beca7cbfc74981795a3218b064
(cherry picked from commit c61576794e)
66 lines
1.7 KiB
C++
66 lines
1.7 KiB
C++
/*
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* Copyright (C) 2007 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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*/
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#ifndef ANDROID_BARRIER_H
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#define ANDROID_BARRIER_H
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#include <stdint.h>
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#include <sys/types.h>
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#include <utils/threads.h>
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namespace android {
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class Barrier
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{
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public:
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inline Barrier() : state(CLOSED) { }
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inline ~Barrier() { }
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// Release any threads waiting at the Barrier.
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// Provides release semantics: preceding loads and stores will be visible
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// to other threads before they wake up.
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void open() {
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Mutex::Autolock _l(lock);
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state = OPENED;
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cv.broadcast();
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}
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// Reset the Barrier, so wait() will block until open() has been called.
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void close() {
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Mutex::Autolock _l(lock);
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state = CLOSED;
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}
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// Wait until the Barrier is OPEN.
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// Provides acquire semantics: no subsequent loads or stores will occur
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// until wait() returns.
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void wait() const {
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Mutex::Autolock _l(lock);
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while (state == CLOSED) {
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cv.wait(lock);
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}
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}
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private:
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enum { OPENED, CLOSED };
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mutable Mutex lock;
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mutable Condition cv;
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volatile int state;
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};
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}; // namespace android
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#endif // ANDROID_BARRIER_H
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