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/*
* Copyright (C) 2012 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef SINGLE_STATE_QUEUE_H
#define SINGLE_STATE_QUEUE_H
// Non-blocking single element state queue, or
// Non-blocking single-reader / single-writer multi-word atomic load / store
#include <stdint.h>
namespace android {
template<typename T> class SingleStateQueue {
public:
class Mutator;
class Observer;
struct Shared {
// needs to be part of a union so don't define constructor or destructor
friend class Mutator;
friend class Observer;
private:
void init() { mAck = 0; mSequence = 0; }
volatile int32_t mAck;
#if 0
int mPad[7];
// cache line boundary
#endif
volatile int32_t mSequence;
T mValue;
};
class Mutator {
public:
Mutator(Shared *shared);
/*virtual*/ ~Mutator() { }
// push new value onto state queue, overwriting previous value;
// returns a sequence number which can be used with ack()
int32_t push(const T& value);
// return true if most recent push has been observed
bool ack();
// return true if a push with specified sequence number or later has been observed
bool ack(int32_t sequence);
private:
int32_t mSequence;
Shared * const mShared;
};
class Observer {
public:
Observer(Shared *shared);
/*virtual*/ ~Observer() { }
// return true if value has changed
bool poll(T& value);
private:
int32_t mSequence;
int mSeed; // for PRNG
Shared * const mShared;
};
#if 0
SingleStateQueue(void /*Shared*/ *shared);
/*virtual*/ ~SingleStateQueue() { }
static size_t size() { return sizeof(Shared); }
#endif
};
} // namespace android
#endif // SINGLE_STATE_QUEUE_H
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