ImageReader: Add discardFreeBuffers method

am: 2e2aaf6e04

Change-Id: I142f1b011a045aa0f5af7c33eb76b059eb67e30d

media/java/android/media/ImageReader.java

@@ -520,6 +520,31 @@ public class ImageReader implements AutoCloseable {
         }
     }
 
+    /**
+     * Discard any free buffers owned by this ImageReader.
+     *
+     * <p>
+     * Generally, the ImageReader caches buffers for reuse once they have been
+     * allocated, for best performance. However, sometimes it may be important to
+     * release all the cached, unused buffers to save on memory.
+     * </p>
+     * <p>
+     * Calling this method will discard all free cached buffers. This does not include any buffers
+     * associated with Images acquired from the ImageReader, any filled buffers waiting to be
+     * acquired, and any buffers currently in use by the source rendering buffers into the
+     * ImageReader's Surface.
+     * <p>
+     * The ImageReader continues to be usable after this call, but may need to reallocate buffers
+     * when more buffers are needed for rendering.
+     * </p>
+     * @hide
+     */
+    public void discardFreeBuffers() {
+        synchronized (mCloseLock) {
+            nativeDiscardFreeBuffers();
+        }
+    }
+
     @Override
     protected void finalize() throws Throwable {
         try {
@@ -872,6 +897,7 @@ public class ImageReader implements AutoCloseable {
     private synchronized native void nativeReleaseImage(Image i);
     private synchronized native Surface nativeGetSurface();
     private synchronized native int nativeDetachImage(Image i);
+    private synchronized native void nativeDiscardFreeBuffers();
 
     /**
      * @return A return code {@code ACQUIRE_*}

media/jni/android_media_ImageReader.cpp

@@ -611,6 +611,23 @@ static jint ImageReader_detachImage(JNIEnv* env, jobject thiz, jobject image) {
     return OK;
 }
 
+static void ImageReader_discardFreeBuffers(JNIEnv* env, jobject thiz) {
+    ALOGV("%s:", __FUNCTION__);
+    JNIImageReaderContext* ctx = ImageReader_getContext(env, thiz);
+    if (ctx == NULL) {
+        jniThrowException(env, "java/lang/IllegalStateException", "ImageReader was already closed");
+        return;
+    }
+
+    BufferItemConsumer* bufferConsumer = ctx->getBufferConsumer();
+    status_t res = bufferConsumer->discardFreeBuffers();
+    if (res != OK) {
+        ALOGE("Buffer discard failed: %s (%d)", strerror(-res), res);
+        jniThrowRuntimeException(env,
+                "nativeDicardFreebuffers failed");
+    }
+}
+
 static jobject ImageReader_getSurface(JNIEnv* env, jobject thiz)
 {
     ALOGV("%s: ", __FUNCTION__);
@@ -773,6 +790,7 @@ static const JNINativeMethod gImageReaderMethods[] = {
     {"nativeImageSetup",       "(Landroid/media/Image;)I",   (void*)ImageReader_imageSetup },
     {"nativeGetSurface",       "()Landroid/view/Surface;",   (void*)ImageReader_getSurface },
     {"nativeDetachImage",      "(Landroid/media/Image;)I",   (void*)ImageReader_detachImage },
+    {"nativeDiscardFreeBuffers", "()V",                      (void*)ImageReader_discardFreeBuffers }
 };
 
 static const JNINativeMethod gImageMethods[] = {