76 lines
2.9 KiB
C++
76 lines
2.9 KiB
C++
/*
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* Copyright (C) 2013 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 SENSOREVENTQUEUE_H_
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#define SENSOREVENTQUEUE_H_
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#include <hardware/sensors.h>
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#include <pthread.h>
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/*
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* Fixed-size circular queue, with an API developed around the sensor HAL poll() method.
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* Poll() takes a pointer to a buffer, which is written by poll() before it returns.
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* This class can provide a pointer to a spot in its internal buffer for poll() to
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* write to, instead of using an intermediate buffer and a memcpy.
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*
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* Thread safety:
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* Reading can be done safely after grabbing the mutex lock, while poll() writing in a separate
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* thread without a mutex lock. But there can only be one writer at a time.
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*/
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class SensorEventQueue {
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int mCapacity;
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int mStart; // start of readable region
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int mSize; // number of readable items
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sensors_event_t* mData;
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pthread_cond_t mSpaceAvailableCondition;
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public:
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SensorEventQueue(int capacity);
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~SensorEventQueue();
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// Returns length of region, between zero and min(capacity, requestedLength). If there is any
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// writable space, it will return a region of at least one. Because it must return
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// a pointer to a contiguous region, it may return smaller regions as we approach the end of
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// the data array.
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// Only call while holding the lock.
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// The region is not marked internally in any way. Subsequent calls may return overlapping
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// regions. This class expects there to be exactly one writer at a time.
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int getWritableRegion(int requestedLength, sensors_event_t** out);
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// After writing to the region returned by getWritableRegion(), call this to indicate how
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// many records were actually written.
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// This increases size() by count.
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// Only call while holding the lock.
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void markAsWritten(int count);
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// Gets the number of readable records.
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// Only call while holding the lock.
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int getSize();
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// Returns pointer to the first readable record, or NULL if size() is zero.
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// Only call this while holding the lock.
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sensors_event_t* peek();
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// This will decrease the size by one, freeing up the oldest readable event's slot for writing.
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// Only call while holding the lock.
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void dequeue();
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// Blocks until space is available. No-op if there is already space.
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// Returns true if it had to wait.
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bool waitForSpace(pthread_mutex_t* mutex);
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};
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#endif // SENSOREVENTQUEUE_H_
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