content: Add DeletedDiscardableSharedMemory IPC.

content/common/host_discardable_shared_memory_manager.h

Index: content/common/host_discardable_shared_memory_manager.h
diff --git a/content/common/host_discardable_shared_memory_manager.h b/content/common/host_discardable_shared_memory_manager.h
index 624dd2fdf164895db32e4427645d28a7b9e3f209..093667a430db597d940bead73dbc8cacf78f3d0c 100644
--- a/content/common/host_discardable_shared_memory_manager.h
+++ b/content/common/host_discardable_shared_memory_manager.h
@@ -7,10 +7,11 @@
 
 #include <vector>
 
+#include "base/containers/hash_tables.h"
 #include "base/memory/discardable_memory_shmem_allocator.h"
 #include "base/memory/discardable_shared_memory.h"
-#include "base/memory/linked_ptr.h"
 #include "base/memory/memory_pressure_listener.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/shared_memory.h"
 #include "base/memory/weak_ptr.h"
 #include "base/process/process_handle.h"
@@ -18,6 +19,7 @@
 #include "content/common/content_export.h"
 
 namespace content {
+typedef int32 DiscardableSharedMemoryId;

[Avi (use Gerrit), 2015/03/16 16:58:21]

First, int32_t, per the deprecation notice in base/basictypes.h. Second, why not
make this a class member:?

[reveman, 2015/03/16 18:30:55]

int32 -> int32_t, Done.

The reason I didn't make it a class member is because it's shared between
ChildDiscardableSharedMemoryManager and this Host class. I think it would be
more correct to move this into it's own header
(content/common/discardable_shared_memory_id.h) and keep the
DiscardableSharedMemoryId name but that felt overkill for a simple typedef.
Another option is to just get rid of it and instead use 'int32_t' everywhere.
Let me know what you think is best.

 
 // Implementation of DiscardableMemoryShmemAllocator that allocates and
 // manages discardable memory segments for the browser process and child
@@ -41,9 +43,15 @@ class CONTENT_EXPORT HostDiscardableSharedMemoryManager
   void AllocateLockedDiscardableSharedMemoryForChild(
       base::ProcessHandle process_handle,
       size_t size,
+      DiscardableSharedMemoryId id,
       base::SharedMemoryHandle* shared_memory_handle);
 
   // Call this to notify the manager that child process associated with
+  // |process_handle| has deleted discardable memory segment with |id|.
+  void ChildDeletedDiscardableSharedMemory(DiscardableSharedMemoryId id,
+                                           base::ProcessHandle process_handle);
+
+  // Call this to notify the manager that child process associated with
   // |process_handle| has been removed. The manager will use this to release
   // memory segments allocated for child process to the OS.
   void ProcessRemoved(base::ProcessHandle process_handle);
@@ -55,26 +63,37 @@ class CONTENT_EXPORT HostDiscardableSharedMemoryManager
   // Reduce memory usage if above current memory limit.
   void EnforceMemoryPolicy();
 
+  // Returns bytes of allocated discardable memory.
+  size_t GetBytesAllocated();
+
  private:
-  struct MemorySegment {
-    MemorySegment(linked_ptr<base::DiscardableSharedMemory> memory,
-                  base::ProcessHandle process_handle);
+  class MemorySegment : public base::RefCountedThreadSafe<MemorySegment> {
+   public:
+    MemorySegment(scoped_ptr<base::DiscardableSharedMemory> memory);
+
+    base::DiscardableSharedMemory* memory() const { return memory_.get(); }
+
+   private:
+    friend class base::RefCountedThreadSafe<MemorySegment>;
+
     ~MemorySegment();
 
-    linked_ptr<base::DiscardableSharedMemory> memory;
-    base::ProcessHandle process_handle;
+    scoped_ptr<base::DiscardableSharedMemory> memory_;
+
+    DISALLOW_COPY_AND_ASSIGN(MemorySegment);
   };
 
-  static bool CompareMemoryUsageTime(const MemorySegment& a,
-                                     const MemorySegment& b) {
+  static bool CompareMemoryUsageTime(const scoped_refptr<MemorySegment>& a,
+                                     const scoped_refptr<MemorySegment>& b) {
     // In this system, LRU memory segment is evicted first.
-    return a.memory->last_known_usage() > b.memory->last_known_usage();
+    return a->memory()->last_known_usage() > b->memory()->last_known_usage();
   }
 
   void OnMemoryPressure(
       base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level);
   void ReduceMemoryUsageUntilWithinMemoryLimit();
   void ReduceMemoryUsageUntilWithinLimit(size_t limit);
+  void ReleaseMemory(base::DiscardableSharedMemory* memory);
   void BytesAllocatedChanged(size_t new_bytes_allocated) const;
 
   // Virtual for tests.
@@ -82,9 +101,13 @@ class CONTENT_EXPORT HostDiscardableSharedMemoryManager
   virtual void ScheduleEnforceMemoryPolicy();
 
   base::Lock lock_;
+  typedef base::hash_map<DiscardableSharedMemoryId,
+                         scoped_refptr<MemorySegment>> MemorySegmentMap;
+  typedef base::hash_map<base::ProcessHandle, MemorySegmentMap> ProcessMap;
+  ProcessMap processes_;
   // Note: The elements in |segments_| are arranged in such a way that they form
   // a heap. The LRU memory segment always first.
-  typedef std::vector<MemorySegment> MemorySegmentVector;
+  typedef std::vector<scoped_refptr<MemorySegment>> MemorySegmentVector;
   MemorySegmentVector segments_;
   size_t memory_limit_;
   size_t bytes_allocated_;