Added a SensorEventQueue, a circular buffer meant for reading with one thread

and polling a subhal with another. The writing thread gets access to pointers
in the internal buffer. This design avoids a memcpy on write when the multihal
fetches subhal events using poll().

Unit-tests include multithreaded reading and writing lots of events, in
random-sized chunks.

This is not used by the multihal yet. That will be a different CL.

Change-Id: I58418d69eebebeb96befb08ba3aed080f0f08551

1 files changed, 110 insertions, 0 deletions

diff --git a/modules/sensors/SensorEventQueue.cpp b/modules/sensors/SensorEventQueue.cpp
new file mode 100644
index 0000000..c139944
--- /dev/null
+++ b/modules/sensors/SensorEventQueue.cpp
@@ -0,0 +1,110 @@
+/*
+ * Copyright (C) 2013 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.
+ */
+
+#include <hardware/sensors.h>
+#include <algorithm>
+#include <pthread.h>
+
+#include <linux/input.h>
+#include <cutils/atomic.h>
+#include <cutils/log.h>
+
+#include "SensorEventQueue.h"
+
+SensorEventQueue::SensorEventQueue(int capacity) {
+    mCapacity = capacity;
+    mStart = 0;
+    mSize = 0;
+    mData = new sensors_event_t[mCapacity];
+    pthread_cond_init(&mDataAvailableCondition, NULL);
+    pthread_cond_init(&mSpaceAvailableCondition, NULL);
+    pthread_mutex_init(&mMutex, NULL);
+}
+
+SensorEventQueue::~SensorEventQueue() {
+    delete[] mData;
+    mData = NULL;
+    pthread_cond_destroy(&mDataAvailableCondition);
+    pthread_cond_destroy(&mSpaceAvailableCondition);
+    pthread_mutex_destroy(&mMutex);
+}
+
+void SensorEventQueue::lock() {
+    pthread_mutex_lock(&mMutex);
+}
+
+void SensorEventQueue::unlock() {
+    pthread_mutex_unlock(&mMutex);
+}
+
+void SensorEventQueue::waitForSpaceAndLock() {
+    lock();
+    while (mSize >= mCapacity) {
+        pthread_cond_wait(&mSpaceAvailableCondition, &mMutex);
+    }
+}
+
+void SensorEventQueue::waitForDataAndLock() {
+    lock();
+    while (mSize <= 0) {
+        pthread_cond_wait(&mDataAvailableCondition, &mMutex);
+    }
+}
+
+int SensorEventQueue::getWritableRegion(int requestedLength, sensors_event_t** out) {
+    if (mSize >= mCapacity || requestedLength <= 0) {
+        *out = NULL;
+        return 0;
+    }
+    // Start writing after the last readable record.
+    int firstWritable = (mStart + mSize) % mCapacity;
+
+    int lastWritable = firstWritable + requestedLength - 1;
+
+    // Don't go past the end of the data array.
+    if (lastWritable > mCapacity - 1) {
+        lastWritable = mCapacity - 1;
+    }
+    // Don't go into the readable region.
+    if (firstWritable < mStart && lastWritable >= mStart) {
+        lastWritable = mStart - 1;
+    }
+    *out = &mData[firstWritable];
+    return lastWritable - firstWritable + 1;
+}
+
+void SensorEventQueue::markAsWritten(int count) {
+    mSize += count;
+    if (mSize) {
+        pthread_cond_broadcast(&mDataAvailableCondition);
+    }
+}
+
+int SensorEventQueue::getSize() {
+    return mSize;
+}
+
+sensors_event_t* SensorEventQueue::peek() {
+    if (mSize <= 0) return NULL;
+    return &mData[mStart];
+}
+
+void SensorEventQueue::dequeue() {
+    if (mSize <= 0) return;
+    mSize--;
+    mStart = (mStart + 1) % mCapacity;
+    pthread_cond_broadcast(&mSpaceAvailableCondition);
+}