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

modules/sensors/tests/SensorEventQueue_test.cpp

@@ -0,0 +1,173 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <hardware/sensors.h>
+#include <pthread.h>
+#include "SensorEventQueue.cpp"
+
+// Unit tests for the SensorEventQueue.
+
+// Run it like this:
+//
+// make sensorstests -j32 && \
+// out/host/linux-x86/obj/EXECUTABLES/sensorstests_intermediates/sensorstests
+
+bool checkWritableBufferSize(SensorEventQueue* queue, int requested, int expected) {
+    sensors_event_t* buffer;
+    int actual = queue->getWritableRegion(requested, &buffer);
+    if (actual != expected) {
+        printf("Expected buffer size was %d; actual was %d\n", expected, actual);
+        return false;
+    }
+    return true;
+}
+
+bool checkSize(SensorEventQueue* queue, int expected) {
+    int actual = queue->getSize();
+    if (actual != expected) {
+        printf("Expected queue size was %d; actual was %d", expected, actual);
+        return false;
+    }
+    return true;
+}
+
+bool testSimpleWriteSizeCounts() {
+    printf("TEST testSimpleWriteSizeCounts\n");
+    SensorEventQueue* queue = new SensorEventQueue(10);
+    if (!checkSize(queue, 0)) return false;
+    if (!checkWritableBufferSize(queue, 11, 10)) return false;
+    if (!checkWritableBufferSize(queue, 10, 10)) return false;
+    if (!checkWritableBufferSize(queue, 9, 9)) return false;
+
+    queue->markAsWritten(7);
+    if (!checkSize(queue, 7)) return false;
+    if (!checkWritableBufferSize(queue, 4, 3)) return false;
+    if (!checkWritableBufferSize(queue, 3, 3)) return false;
+    if (!checkWritableBufferSize(queue, 2, 2)) return false;
+
+    queue->markAsWritten(3);
+    if (!checkSize(queue, 10)) return false;
+    if (!checkWritableBufferSize(queue, 1, 0)) return false;
+
+    printf("passed\n");
+    return true;
+}
+
+bool testWrappingWriteSizeCounts() {
+    printf("TEST testWrappingWriteSizeCounts\n");
+    SensorEventQueue* queue = new SensorEventQueue(10);
+    queue->markAsWritten(9);
+    if (!checkSize(queue, 9)) return false;
+
+    // dequeue from the front
+    queue->dequeue();
+    queue->dequeue();
+    if (!checkSize(queue, 7)) return false;
+    if (!checkWritableBufferSize(queue, 100, 1)) return false;
+
+    // Write all the way to the end.
+    queue->markAsWritten(1);
+    if (!checkSize(queue, 8)) return false;
+    // Now the two free spots in the front are available.
+    if (!checkWritableBufferSize(queue, 100, 2)) return false;
+
+    // Fill the queue again
+    queue->markAsWritten(2);
+    if (!checkSize(queue, 10)) return false;
+
+    printf("passed\n");
+    return true;
+}
+
+static const int TTOQ_EVENT_COUNT = 10000;
+
+struct TaskContext {
+  bool success;
+  SensorEventQueue* queue;
+};
+
+void* writerTask(void* ptr) {
+    printf("writerTask starts\n");
+    TaskContext* ctx = (TaskContext*)ptr;
+    SensorEventQueue* queue = ctx->queue;
+    int totalWrites = 0;
+    sensors_event_t* buffer;
+    while (totalWrites < TTOQ_EVENT_COUNT) {
+        queue->waitForSpaceAndLock();
+        int writableSize = queue->getWritableRegion(rand() % 10 + 1, &buffer);
+        queue->unlock();
+        for (int i = 0; i < writableSize; i++) {
+            // serialize the events
+            buffer[i].timestamp = totalWrites++;
+        }
+        queue->lock();
+        queue->markAsWritten(writableSize);
+        queue->unlock();
+    }
+    printf("writerTask ends normally\n");
+    return NULL;
+}
+
+void* readerTask(void* ptr) {
+    printf("readerTask starts\n");
+    TaskContext* ctx = (TaskContext*)ptr;
+    SensorEventQueue* queue = ctx->queue;
+    int totalReads = 0;
+    while (totalReads < TTOQ_EVENT_COUNT) {
+        queue->waitForDataAndLock();
+        int maxReads = rand() % 20 + 1;
+        int reads = 0;
+        while (queue->getSize() && reads < maxReads) {
+            sensors_event_t* event = queue->peek();
+            if (totalReads != event->timestamp) {
+                printf("FAILURE: readerTask expected timestamp %d; actual was %d\n",
+                        totalReads, (int)(event->timestamp));
+                ctx->success = false;
+                return NULL;
+            }
+            queue->dequeue();
+            totalReads++;
+            reads++;
+        }
+        queue->unlock();
+    }
+    printf("readerTask ends normally\n");
+    return NULL;
+}
+
+
+// Create a short queue, and write and read a ton of data through it.
+// Write serial timestamps into the events, and expect to read them in the right order.
+bool testTwoThreadsOneQueue() {
+    printf("TEST testTwoThreadsOneQueue\n");
+    SensorEventQueue* queue = new SensorEventQueue(100);
+
+    TaskContext readerCtx;
+    readerCtx.success = true;
+    readerCtx.queue = queue;
+
+    TaskContext writerCtx;
+    writerCtx.success = true;
+    writerCtx.queue = queue;
+
+    pthread_t writer, reader;
+    pthread_create(&reader, NULL, readerTask, &readerCtx);
+    pthread_create(&writer, NULL, writerTask, &writerCtx);
+
+    pthread_join(writer, NULL);
+    pthread_join(reader, NULL);
+
+    printf("testTwoThreadsOneQueue done\n");
+    return readerCtx.success && writerCtx.success;
+}
+
+
+int main(int argc, char **argv) {
+    if (testSimpleWriteSizeCounts() &&
+            testWrappingWriteSizeCounts() &&
+            testTwoThreadsOneQueue()) {
+        printf("ALL PASSED\n");
+    } else {
+        printf("SOMETHING FAILED\n");
+    }
+    return EXIT_SUCCESS;
+}