Push HWC cache slot generation down into CompositionEngine

Stop caching buffers inside SurfaceFlinger and remove the tight coupling
between SurfaceFlinger's ClientCache and the Hardware Composer cache.
This allows a better seperation of responsibility, where buffer cache
management is not split between HwcSlotGenerator and HwcBufferCache, but
is instead solely handled by HwcBufferCache.

Note that FramebufferSurface and VirtualDisplaySurface no longer use
HwcBufferCache, but instead use their own cache slot management that
is solely based on BufferQueue slot numbers.

Also do minor refactoring in FramebufferSurface to simplify code.

Bug: 258196272
Test: started and stopped multiple YouTube videos on adt4 and verified
no change in graphic buffer usage
Test: atest HwcBufferCacheTest
Test: atest OutputPrepareTest

Change-Id: Ica7955ab4bc70e3c70207390e36dff73a2fc4949

1 files changed, 6 insertions, 2 deletions

diff --git a/services/surfaceflinger/ClientCache.cpp b/services/surfaceflinger/ClientCache.cpp
index 2bd8f324e1..09e41ffede 100644
--- a/services/surfaceflinger/ClientCache.cpp
+++ b/services/surfaceflinger/ClientCache.cpp
@@ -118,7 +118,8 @@ ClientCache::add(const client_cache_t& cacheId, const sp<GraphicBuffer>& buffer)
                                                                  Usage::READABLE));
 }
 
-void ClientCache::erase(const client_cache_t& cacheId) {
+sp<GraphicBuffer> ClientCache::erase(const client_cache_t& cacheId) {
+    sp<GraphicBuffer> buffer;
     auto& [processToken, id] = cacheId;
     std::vector<sp<ErasedRecipient>> pendingErase;
     {
@@ -126,9 +127,11 @@ void ClientCache::erase(const client_cache_t& cacheId) {
         ClientCacheBuffer* buf = nullptr;
         if (!getBuffer(cacheId, &buf)) {
             ALOGE("failed to erase buffer, could not retrieve buffer");
-            return;
+            return nullptr;
         }
 
+        buffer = buf->buffer->getBuffer();
+
         for (auto& recipient : buf->recipients) {
             sp<ErasedRecipient> erasedRecipient = recipient.promote();
             if (erasedRecipient) {
@@ -142,6 +145,7 @@ void ClientCache::erase(const client_cache_t& cacheId) {
     for (auto& recipient : pendingErase) {
         recipient->bufferErased(cacheId);
     }
+    return buffer;
 }
 
 std::shared_ptr<renderengine::ExternalTexture> ClientCache::get(const client_cache_t& cacheId) {