From 8507586903fa803abf535853a169913f2cf2e555 Mon Sep 17 00:00:00 2001
From: Andy McFadden <fadden@android.com>
Date: Fri, 18 Oct 2013 15:50:24 -0700
Subject: [PATCH] Wait for buffers to drain

When a BufferQueue producer disconnects and reconnects, we retain
the previously-queued buffers but empty the slots.  This allows
the number of queued buffers to grow without limit.  The low-memory
killer does not approve.

Bug 11069934

Change-Id: Ia2eaa954c7a3904b54209a3701dba01689e204d8
---
 libs/gui/BufferQueue.cpp | 45 ++++++++++++++++++++++++++--------------
 1 file changed, 29 insertions(+), 16 deletions(-)

diff --git a/libs/gui/BufferQueue.cpp b/libs/gui/BufferQueue.cpp
index c165a6820..2aecb6778 100644
--- a/libs/gui/BufferQueue.cpp
+++ b/libs/gui/BufferQueue.cpp
@@ -644,6 +644,7 @@ status_t BufferQueue::connect(const sp<IBinder>& token,
             producerControlledByApp ? "true" : "false");
     Mutex::Autolock lock(mMutex);
 
+retry:
     if (mAbandoned) {
         ST_LOGE("connect: BufferQueue has been abandoned!");
         return NO_INIT;
@@ -654,29 +655,41 @@ status_t BufferQueue::connect(const sp<IBinder>& token,
         return NO_INIT;
     }
 
+    if (mConnectedApi != NO_CONNECTED_API) {
+        ST_LOGE("connect: already connected (cur=%d, req=%d)",
+                mConnectedApi, api);
+        return -EINVAL;
+    }
+
+    // If we disconnect and reconnect quickly, we can be in a state where our slots are
+    // empty but we have many buffers in the queue.  This can cause us to run out of
+    // memory if we outrun the consumer.  Wait here if it looks like we have too many
+    // buffers queued up.
+    int maxBufferCount = getMaxBufferCountLocked(false);    // worst-case, i.e. largest value
+    if (mQueue.size() > (size_t) maxBufferCount) {
+        // TODO: make this bound tighter?
+        ST_LOGV("queue size is %d, waiting", mQueue.size());
+        mDequeueCondition.wait(mMutex);
+        goto retry;
+    }
+
     int err = NO_ERROR;
     switch (api) {
         case NATIVE_WINDOW_API_EGL:
         case NATIVE_WINDOW_API_CPU:
         case NATIVE_WINDOW_API_MEDIA:
         case NATIVE_WINDOW_API_CAMERA:
-            if (mConnectedApi != NO_CONNECTED_API) {
-                ST_LOGE("connect: already connected (cur=%d, req=%d)",
-                        mConnectedApi, api);
-                err = -EINVAL;
-            } else {
-                mConnectedApi = api;
-                output->inflate(mDefaultWidth, mDefaultHeight, mTransformHint, mQueue.size());
+            mConnectedApi = api;
+            output->inflate(mDefaultWidth, mDefaultHeight, mTransformHint, mQueue.size());
 
-                // set-up a death notification so that we can disconnect
-                // automatically when/if the remote producer dies.
-                if (token != NULL && token->remoteBinder() != NULL) {
-                    status_t err = token->linkToDeath(static_cast<IBinder::DeathRecipient*>(this));
-                    if (err == NO_ERROR) {
-                        mConnectedProducerToken = token;
-                    } else {
-                        ALOGE("linkToDeath failed: %s (%d)", strerror(-err), err);
-                    }
+            // set-up a death notification so that we can disconnect
+            // automatically when/if the remote producer dies.
+            if (token != NULL && token->remoteBinder() != NULL) {
+                status_t err = token->linkToDeath(static_cast<IBinder::DeathRecipient*>(this));
+                if (err == NO_ERROR) {
+                    mConnectedProducerToken = token;
+                } else {
+                    ALOGE("linkToDeath failed: %s (%d)", strerror(-err), err);
                 }
             }
             break;