Use a lock to deal with concurrent access to the m_evictedBackings

cc/prioritized_resource_manager.h

Index: cc/prioritized_resource_manager.h
diff --git a/cc/prioritized_resource_manager.h b/cc/prioritized_resource_manager.h
index 0256f90bf839f3f7fb874be34b99a6698ba3f7ad..d413fc0ac3f064bc17286fb12d727e600088b295 100644
--- a/cc/prioritized_resource_manager.h
+++ b/cc/prioritized_resource_manager.h
@@ -11,6 +11,7 @@
 #include "base/basictypes.h"
 #include "base/hash_tables.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/synchronization/lock.h"
 #include "cc/cc_export.h"
 #include "cc/proxy.h"
 #include "cc/prioritized_resource.h"
@@ -82,16 +83,16 @@ public:
     // be called on the impl thread while the main thread is running. Returns true if resources are
     // indeed evicted as a result of this call.
     bool reduceMemoryOnImplThread(size_t limitBytes, int priorityCutoff, ResourceProvider*);
+
     // Returns true if there exist any textures that are linked to backings that have had their
     // resources evicted. Only when we commit a tree that has no textures linked to evicted backings
-    // may we allow drawing.
-    bool linkedEvictedBackingsExist() const;
-    // Retrieve the list of all contents textures' backings that have been evicted, to pass to the
-    // main thread to unlink them from their owning textures.
-    void getEvictedBackings(BackingList& evictedBackings);
-    // Unlink the list of contents textures' backings from their owning textures on the main thread
-    // before updating layers.
-    void unlinkEvictedBackings(const BackingList& evictedBackings);
+    // may we allow drawing. After an eviction, this will not become true until
+    // unlinkAndClearEvictedBackings is called.
+    bool linkedEvictedBackingsExist();
+
+    // Unlink the list of contents textures' backings from their owning textures and delete the evicted
+    // backings' structures. This is called just before updating layers.
+    void unlinkAndClearEvictedBackings();

[jamesr, 2012/11/29 22:06:16]

You should document that this can be called from multiple threads

[piman, 2012/11/29 22:24:09]

Wait, this should only be called from the main thread, right?

[ccameron, 2012/11/29 22:25:35]

This one can only be called on the main thread -- I've added a comment to this
effect.

 
     bool requestLate(PrioritizedResource*);
 
@@ -159,7 +160,6 @@ private:
                                      ResourceProvider*);
     PrioritizedResource::Backing* createBacking(gfx::Size, GLenum format, ResourceProvider*);
     void evictFirstBackingResource(ResourceProvider*);
-    void deleteAllEvictedBackings();
     void sortBackings();
 
     void assertInvariants();
@@ -188,7 +188,12 @@ private:
     // are not sorted by priority.
     BackingList m_backings;
     bool m_backingsTailNotSorted;
+
+    // The list of backings that have been evicted, but may still be linked
+    // to textures. This can be accessed concurrently by the main and impl
+    // threads, and may only be accessed while holding m_evictedBackingsLock.
     BackingList m_evictedBackings;
+    base::Lock m_evictedBackingsLock;
 
     TextureVector m_tempTextureVector;