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      1 /*
      2  * Copyright 2016 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef FIFO_FIFO_CONTROLLER_INDIRECT_H
     18 #define FIFO_FIFO_CONTROLLER_INDIRECT_H
     19 
     20 #include <stdint.h>
     21 #include <atomic>
     22 
     23 #include "FifoControllerBase.h"
     24 
     25 namespace android {
     26 
     27 /**
     28  * A FifoControllerBase with counters external to the class.
     29  *
     30  * The actual copunters may be stored in separate regions of shared memory
     31  * with different access rights.
     32  */
     33 class FifoControllerIndirect : public FifoControllerBase {
     34 
     35 public:
     36     FifoControllerIndirect(fifo_frames_t capacity,
     37                            fifo_frames_t threshold,
     38                            fifo_counter_t * readCounterAddress,
     39                            fifo_counter_t * writeCounterAddress)
     40         : FifoControllerBase(capacity, threshold)
     41         , mReadCounterAddress((std::atomic<fifo_counter_t> *) readCounterAddress)
     42         , mWriteCounterAddress((std::atomic<fifo_counter_t> *) writeCounterAddress)
     43     {
     44         setReadCounter(0);
     45         setWriteCounter(0);
     46     }
     47     virtual ~FifoControllerIndirect() {};
     48 
     49     // TODO review use of memory barriers, probably incorrect
     50     virtual fifo_counter_t getReadCounter() override {
     51         return mReadCounterAddress->load(std::memory_order_acquire);
     52     }
     53 
     54     virtual void setReadCounter(fifo_counter_t count) override {
     55         mReadCounterAddress->store(count, std::memory_order_release);
     56     }
     57 
     58     virtual fifo_counter_t getWriteCounter() override {
     59         return mWriteCounterAddress->load(std::memory_order_acquire);
     60     }
     61 
     62     virtual void setWriteCounter(fifo_counter_t count) override {
     63         mWriteCounterAddress->store(count, std::memory_order_release);
     64     }
     65 
     66 private:
     67     std::atomic<fifo_counter_t> * mReadCounterAddress;
     68     std::atomic<fifo_counter_t> * mWriteCounterAddress;
     69 };
     70 
     71 }  // android
     72 
     73 #endif //FIFO_FIFO_CONTROLLER_INDIRECT_H
     74