Cache Backend Proxy to intercept all cache events from the IO thread.

net/disk_cache/tracing_cache_backend.h

Index: net/disk_cache/tracing_cache_backend.h
diff --git a/net/disk_cache/tracing_cache_backend.h b/net/disk_cache/tracing_cache_backend.h
new file mode 100644
index 0000000000000000000000000000000000000000..4bbb0e152cea870481460cf8bd4060bbdec35cc9
--- /dev/null
+++ b/net/disk_cache/tracing_cache_backend.h
@@ -0,0 +1,99 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_DISK_CACHE_TRACING_CACHE_BACKEND_H_
+#define NET_DISK_CACHE_TRACING_CACHE_BACKEND_H_
+
+#include "base/memory/weak_ptr.h"
+#include "net/disk_cache/disk_cache.h"
+#include "net/disk_cache/stats.h"
+
+namespace disk_cache {
+
+class EntryProxy;
+
+// The TracingCacheBackend implements the Cache Backend interface. It intercepts
+// all backend operations from the IO thread and records the time from the start
+// of the operation until the result is delivered.
+class NET_EXPORT TracingCacheBackend : public Backend,
+    public base::SupportsWeakPtr<TracingCacheBackend> {
+ public:
+  explicit TracingCacheBackend(Backend* backend);
+
+  virtual net::CacheType GetCacheType() const OVERRIDE;
+  virtual int32 GetEntryCount() const OVERRIDE;
+  virtual int OpenEntry(const std::string& key, Entry** entry,
+                        const CompletionCallback& callback) OVERRIDE;
+  virtual int CreateEntry(const std::string& key, Entry** entry,
+                          const CompletionCallback& callback) OVERRIDE;
+  virtual int DoomEntry(const std::string& key,
+                        const CompletionCallback& callback) OVERRIDE;
+  virtual int DoomAllEntries(const CompletionCallback& callback) OVERRIDE;
+  virtual int DoomEntriesBetween(base::Time initial_time,
+                                 base::Time end_time,
+                                 const CompletionCallback& callback) OVERRIDE;
+  virtual int DoomEntriesSince(base::Time initial_time,
+                               const CompletionCallback& callback) OVERRIDE;
+  virtual int OpenNextEntry(void** iter, Entry** next_entry,
+                            const CompletionCallback& callback) OVERRIDE;
+  virtual void EndEnumeration(void** iter) OVERRIDE;
+  virtual void GetStats(StatsItems* stats) OVERRIDE;
+  virtual void OnExternalCacheHit(const std::string& key) OVERRIDE;
+
+ private:
+  friend class EntryProxy;
+  enum Operation {
+    OP_NONE = 0,
+    OP_INIT,
+    OP_OPEN,
+    OP_CREATE,
+    OP_DOOM,
+    OP_DOOM_ALL,
+    OP_DOOM_BETWEEN,
+    OP_DOOM_SINCE,
+    OP_OPEN_NEXT,
+    OP_OPEN_PREV,

[rvargas (doing something else), 2013/04/09 18:54:01]

what's this? :)

[pasko-google - do not use, 2013/04/10 17:06:38]

seems like an outdated operation not invoked for the current backend 

+    OP_END_ENUMERATION,
+    OP_ON_EXTERNAL_CACHE_HIT,
+    OP_CLOSE_ENTRY,
+    OP_DOOM_ENTRY,
+    OP_FLUSH_QUEUE,

[rvargas (doing something else), 2013/04/09 18:54:01]

ditto (etc). This is a good place to only have what you intend to track.

[pasko-google - do not use, 2013/04/10 17:06:38]

I do not like putting the decision about the set of supported operations in this
CL because it is not hooked in the code, hence the intentions are not 100%
clear.

So I am now leaving here only the values that are needed for this specific CL
and will extend later as more tracing arrives.

+    OP_RUN_TASK,
+    OP_MAX_BACKEND,
+    OP_READ,
+    OP_WRITE,
+    OP_READ_SPARSE,
+    OP_WRITE_SPARSE,
+    OP_GET_RANGE,
+    OP_CANCEL_IO,
+    OP_IS_READY
+  };
+
+  virtual ~TracingCacheBackend();
+
+  EntryProxy* FindOrCreateEntryProxy(Entry* entry);
+
+  void OnDeleteEntry(Entry* e);
+
+  void RecordEvent(int64 start_time, Operation op, std::string key,
+                   Entry* entry, int rv);
+
+  void BackendOpComplete(int64 start_time, Operation op, std::string key,
+                         Entry** entry, const CompletionCallback& callback,
+                         int rv);
+
+  net::CompletionCallback BindCompletion(Operation op, int64 start_time,
+                                         const std::string& key, Entry **entry,
+                                         const net::CompletionCallback& cb);
+
+  scoped_ptr<Backend> backend_;
+  typedef std::map<Entry*, EntryProxy*> EntryToProxyMap;
+  EntryToProxyMap open_entries_;
+
+  DISALLOW_COPY_AND_ASSIGN(TracingCacheBackend);
+};
+
+}  // namespace disk_cache
+
+#endif  // NET_DISK_CACHE_TRACING_CACHE_BACKEND_H_