From 0e7f4292c78ef32643fdb10134e91e84067515fc Mon Sep 17 00:00:00 2001
From: Mathias Agopian <mathias@google.com>
Date: Thu, 26 Aug 2010 17:42:27 -0700
Subject: [PATCH] fix a race in SF buffer management

also remove some unused code.

Change-Id: Iae2c3309b7a08055f3e13a5b866c5c084993e352
---
 .../surfaceflinger/SharedBufferStack.h        |  6 ++++-
 .../SharedBufferStack.cpp                     | 24 +++++++++----------
 2 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/include/private/surfaceflinger/SharedBufferStack.h b/include/private/surfaceflinger/SharedBufferStack.h
index d016dfa96..d68966791 100644
--- a/include/private/surfaceflinger/SharedBufferStack.h
+++ b/include/private/surfaceflinger/SharedBufferStack.h
@@ -151,7 +151,6 @@ public:
     ~SharedBufferBase();
     status_t getStatus() const;
     int32_t getIdentity() const;
-    size_t getFrontBuffer() const;
     String8 dump(char const* prefix) const;
 
 protected:
@@ -226,6 +225,11 @@ private:
         inline ssize_t operator()();
     };
 
+    struct DequeueUpdate : public UpdateBase {
+        inline DequeueUpdate(SharedBufferBase* sbb);
+        inline ssize_t operator()();
+    };
+
     struct UndoDequeueUpdate : public UpdateBase {
         inline UndoDequeueUpdate(SharedBufferBase* sbb);
         inline ssize_t operator()();
diff --git a/libs/surfaceflinger_client/SharedBufferStack.cpp b/libs/surfaceflinger_client/SharedBufferStack.cpp
index 4ad9f861c..38b2faec8 100644
--- a/libs/surfaceflinger_client/SharedBufferStack.cpp
+++ b/libs/surfaceflinger_client/SharedBufferStack.cpp
@@ -191,12 +191,6 @@ int32_t SharedBufferBase::getIdentity() const
     return stack.identity;
 }
 
-size_t SharedBufferBase::getFrontBuffer() const
-{
-    SharedBufferStack& stack( *mSharedStack );
-    return size_t( stack.head );
-}
-
 String8 SharedBufferBase::dump(char const* prefix) const
 {
     const size_t SIZE = 1024;
@@ -281,6 +275,16 @@ ssize_t SharedBufferClient::QueueUpdate::operator()() {
     return NO_ERROR;
 }
 
+SharedBufferClient::DequeueUpdate::DequeueUpdate(SharedBufferBase* sbb)
+    : UpdateBase(sbb) {
+}
+ssize_t SharedBufferClient::DequeueUpdate::operator()() {
+    if (android_atomic_dec(&stack.available) == 0) {
+        LOGW("dequeue probably called from multiple threads!");
+    }
+    return NO_ERROR;
+}
+
 SharedBufferClient::UndoDequeueUpdate::UndoDequeueUpdate(SharedBufferBase* sbb)
     : UpdateBase(sbb) {    
 }
@@ -388,12 +392,8 @@ ssize_t SharedBufferClient::dequeue()
     if (err != NO_ERROR)
         return ssize_t(err);
 
-    // NOTE: 'stack.available' is part of the conditions, however
-    // decrementing it, never changes any conditions, so we don't need
-    // to do this as part of an update.
-    if (android_atomic_dec(&stack.available) == 0) {
-        LOGW("dequeue probably called from multiple threads!");
-    }
+    DequeueUpdate update(this);
+    updateCondition( update );
 
     undoDequeueTail = tail;
     int dequeued = stack.index[tail];