fix a memory leak and memory corruption in RefBase

we would leak a weakref_impl if a RefBase was never incWeak()'ed.
there was also a dangling pointer that would cause memory corruption
and double-delete when a custom destroyer was used to delay the
execution of ~RefBase.

it turns out that the custom destroyer feature caused most of the
problems, so it's now gone. The only client was SurfaceFlinger
who now handles things on its own.

RefBase is essentially back its "gingerbread" state, but the
code was slightly cleaned-up.

Bug: 5151207, 5084978
Change-Id: Id6ef1d707f96d96366f75068f77b30e0ce2722a5

1 files changed, 39 insertions, 44 deletions

diff --git a/libs/utils/RefBase.cpp b/libs/utils/RefBase.cpp
index 8db2009..37d061c 100644
--- a/libs/utils/RefBase.cpp
+++ b/libs/utils/RefBase.cpp
@@ -49,11 +49,6 @@ namespace android {
 
 // ---------------------------------------------------------------------------
 
-RefBase::Destroyer::~Destroyer() {
-}
-
-// ---------------------------------------------------------------------------
-
 class RefBase::weakref_impl : public RefBase::weakref_type
 {
 public:
@@ -61,7 +56,6 @@ public:
     volatile int32_t    mWeak;
     RefBase* const      mBase;
     volatile int32_t    mFlags;
-    Destroyer*          mDestroyer;
 
 #if !DEBUG_REFS
 
@@ -70,7 +64,6 @@ public:
         , mWeak(0)
         , mBase(base)
         , mFlags(0)
-        , mDestroyer(0)
     {
     }
 
@@ -113,7 +106,7 @@ public:
                 LOGD("\t%c ID %p (ref %d):", inc, refs->id, refs->ref);
 #if DEBUG_REFS_CALLSTACK_ENABLED
                 refs->stack.dump();
-#endif;
+#endif
                 refs = refs->next;
             }
         }
@@ -131,7 +124,7 @@ public:
                 LOGD("\t%c ID %p (ref %d):", inc, refs->id, refs->ref);
 #if DEBUG_REFS_CALLSTACK_ENABLED
                 refs->stack.dump();
-#endif;
+#endif
                 refs = refs->next;
             }
         }
@@ -193,7 +186,7 @@ public:
         String8 text;
 
         {
-            Mutex::Autolock _l(const_cast<weakref_impl*>(this)->mMutex);
+            Mutex::Autolock _l(mMutex);
             char buf[128];
             sprintf(buf, "Strong references on RefBase %p (weakref_type %p):\n", mBase, this);
             text.append(buf);
@@ -318,7 +311,7 @@ private:
         }
     }
 
-    Mutex mMutex;
+    mutable Mutex mMutex;
     ref_entry* mStrongRefs;
     ref_entry* mWeakRefs;
 
@@ -348,7 +341,7 @@ void RefBase::incStrong(const void* id) const
     }
 
     android_atomic_add(-INITIAL_STRONG_VALUE, &refs->mStrong);
-    const_cast<RefBase*>(this)->onFirstRef();
+    refs->mBase->onFirstRef();
 }
 
 void RefBase::decStrong(const void* id) const
@@ -361,13 +354,9 @@ void RefBase::decStrong(const void* id) const
 #endif
     LOG_ASSERT(c >= 1, "decStrong() called on %p too many times", refs);
     if (c == 1) {
-        const_cast<RefBase*>(this)->onLastStrongRef(id);
-        if ((refs->mFlags&OBJECT_LIFETIME_WEAK) != OBJECT_LIFETIME_WEAK) {
-            if (refs->mDestroyer) {
-                refs->mDestroyer->destroy(this);
-            } else {
-                delete this;
-            }
+        refs->mBase->onLastStrongRef(id);
+        if ((refs->mFlags&OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_STRONG) {
+            delete this;
         }
     }
     refs->decWeak(id);
@@ -391,7 +380,7 @@ void RefBase::forceIncStrong(const void* id) const
         android_atomic_add(-INITIAL_STRONG_VALUE, &refs->mStrong);
         // fall through...
     case 0:
-        const_cast<RefBase*>(this)->onFirstRef();
+        refs->mBase->onFirstRef();
     }
 }
 
@@ -400,10 +389,6 @@ int32_t RefBase::getStrongCount() const
     return mRefs->mStrong;
 }
 
-void RefBase::setDestroyer(RefBase::Destroyer* destroyer) {
-    mRefs->mDestroyer = destroyer;
-}
-
 RefBase* RefBase::weakref_type::refBase() const
 {
     return static_cast<const weakref_impl*>(this)->mBase;
@@ -417,6 +402,7 @@ void RefBase::weakref_type::incWeak(const void* id)
     LOG_ASSERT(c >= 0, "incWeak called on %p after last weak ref", this);
 }
 
+
 void RefBase::weakref_type::decWeak(const void* id)
 {
     weakref_impl* const impl = static_cast<weakref_impl*>(this);
@@ -424,30 +410,27 @@ void RefBase::weakref_type::decWeak(const void* id)
     const int32_t c = android_atomic_dec(&impl->mWeak);
     LOG_ASSERT(c >= 1, "decWeak called on %p too many times", this);
     if (c != 1) return;
-    
-    if ((impl->mFlags&OBJECT_LIFETIME_WEAK) != OBJECT_LIFETIME_WEAK) {
+
+    if ((impl->mFlags&OBJECT_LIFETIME_WEAK) == OBJECT_LIFETIME_STRONG) {
+        // This is the regular lifetime case. The object is destroyed
+        // when the last strong reference goes away. Since weakref_impl
+        // outlive the object, it is not destroyed in the dtor, and
+        // we'll have to do it here.
         if (impl->mStrong == INITIAL_STRONG_VALUE) {
-            if (impl->mBase) {
-                if (impl->mDestroyer) {
-                    impl->mDestroyer->destroy(impl->mBase);
-                } else {
-                    delete impl->mBase;
-                }
-            }
+            // Special case: we never had a strong reference, so we need to
+            // destroy the object now.
+            delete impl->mBase;
         } else {
             // LOGV("Freeing refs %p of old RefBase %p\n", this, impl->mBase);
             delete impl;
         }
     } else {
+        // less common case: lifetime is OBJECT_LIFETIME_{WEAK|FOREVER}
         impl->mBase->onLastWeakRef(id);
-        if ((impl->mFlags&OBJECT_LIFETIME_FOREVER) != OBJECT_LIFETIME_FOREVER) {
-            if (impl->mBase) {
-                if (impl->mDestroyer) {
-                    impl->mDestroyer->destroy(impl->mBase);
-                } else {
-                    delete impl->mBase;
-                }
-            }
+        if ((impl->mFlags&OBJECT_LIFETIME_MASK) == OBJECT_LIFETIME_WEAK) {
+            // this is the OBJECT_LIFETIME_WEAK case. The last weak-reference
+            // is gone, we can destroy the object.
+            delete impl->mBase;
         }
     }
 }
@@ -569,11 +552,23 @@ RefBase::RefBase()
 
 RefBase::~RefBase()
 {
-    if ((mRefs->mFlags & OBJECT_LIFETIME_WEAK) == OBJECT_LIFETIME_WEAK) {
-        if (mRefs->mWeak == 0) {
-            delete mRefs;
+    if (mRefs->mStrong == INITIAL_STRONG_VALUE) {
+        // we never acquired a strong (and/or weak) reference on this object.
+        delete mRefs;
+    } else {
+        // life-time of this object is extended to WEAK or FOREVER, in
+        // which case weakref_impl doesn't out-live the object and we
+        // can free it now.
+        if ((mRefs->mFlags & OBJECT_LIFETIME_MASK) != OBJECT_LIFETIME_STRONG) {
+            // It's possible that the weak count is not 0 if the object
+            // re-acquired a weak reference in its destructor
+            if (mRefs->mWeak == 0) {
+                delete mRefs;
+            }
         }
     }
+    // for debugging purposes, clear this.
+    const_cast<weakref_impl*&>(mRefs) = NULL;
 }
 
 void RefBase::extendObjectLifetime(int32_t mode)