[Not for review] Discardable memory emulation

base/memory/discardable_memory.h

Index: base/memory/discardable_memory.h
diff --git a/base/memory/discardable_memory.h b/base/memory/discardable_memory.h
index d6e91b979d5a46fdd50e6ef07ab4f52a904bc042..4d3fbec3654b0ccd7e3a0381572b32b17cab1c9e 100644
--- a/base/memory/discardable_memory.h
+++ b/base/memory/discardable_memory.h
@@ -17,6 +17,11 @@ enum LockDiscardableMemoryStatus {
   DISCARDABLE_MEMORY_SUCCESS = 1
 };
 
+#if !defined(OS_ANDROID) && !defined(OS_MACOSX)

[nduca, 2013/05/29 13:57:00]

so, on windows 8, we have discardable memory but pre-8 we dont. How does the
provider fit in in that case?

maybe we can put everything behind a provider interface somehow?

[Ian Vollick, 2013/06/06 00:21:47]

I *think* this is done, but please let me know if my approach isn't what you
were hoping for.

+// Used to emulate discardable memory on unsupported platforms.
+class DiscardableMemoryProvider;
+#endif
+
 // Platform abstraction for discardable memory. DiscardableMemory is used to
 // cache large objects without worrying about blowing out memory, both on mobile
 // devices where there is no swap, and desktop devices where unused free memory
@@ -54,6 +59,11 @@ class BASE_EXPORT DiscardableMemory {
   // Check whether the system supports discardable memory.
   static bool Supported();
 
+#if !defined(OS_ANDROID) && !defined(OS_MACOSX)
+  // Installs a provider to emulate discardable memory on unsupported platforms.
+  static void SetProvider(DiscardableMemoryProvider* provider);
+#endif
+
   // Initialize the DiscardableMemory object. On success, this function returns
   // true and the memory is locked. This should only be called once.
   // This call could fail because of platform-specific limitations and the user
@@ -103,16 +113,31 @@ class BASE_EXPORT DiscardableMemory {
   void ReleaseFileDescriptor();
 #endif  // OS_ANDROID
 
+#if defined(OS_ANDROID) || defined(OS_MACOSX)

[jonathan.backer, 2013/05/29 14:02:54]

Maybe a #define DISCARDABLE_MEMORY_SUPPORTED defined(OS_ANDROID) ||
defined(OS_MACOSX)?

[Ian Vollick, 2013/06/06 00:21:47]

Done.

   void* memory_;
   size_t size_;
   bool is_locked_;
 #if defined(OS_ANDROID)
   int fd_;
 #endif  // OS_ANDROID
+#endif  // OS_ANDROID || OS_MACOSX
 
   DISALLOW_COPY_AND_ASSIGN(DiscardableMemory);
 };
 
+#if !defined(OS_ANDROID) && !defined(OS_MACOSX)
+class BASE_EXPORT DiscardableMemoryProvider {
+ public:
+  virtual bool Register(const DiscardableMemory*, size_t size) = 0;
+  virtual void Unregister(const DiscardableMemory*) = 0;
+  virtual LockDiscardableMemoryStatus Lock(const DiscardableMemory*) = 0;
+  virtual void Unlock(const DiscardableMemory*) = 0;
+  virtual void* Memory(const DiscardableMemory*) const = 0;
+  virtual bool PurgeForTestingSupported() const = 0;
+  virtual void PurgeForTesting() = 0;
+};
+#endif
+
 }  // namespace base
 
 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_H_