SSLClientSessionCache: Log number of times Lookup is called per Session.

net/ssl/ssl_client_session_cache.h

 // Copyright 2015 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_SSL_SSL_CLIENT_SESSION_CACHE_H_
 #define NET_SSL_SSL_CLIENT_SESSION_CACHE_H_
 
 #include <stddef.h>
 #include <time.h>
 
@@ skipping 31 matching lines @@
 
   explicit SSLClientSessionCache(const Config& config);
   ~SSLClientSessionCache() override;
 
   size_t size() const;
 
   // Returns the session associated with |cache_key| and moves it to the front
   // of the MRU list. Returns nullptr if there is none.
   bssl::UniquePtr<SSL_SESSION> Lookup(const std::string& cache_key);
 
+  // If Lookup returns a non-null pointer, this method must be called once the
+  // TLS handshake done with the session from Lookup has completed. If
+  // |should_log| is true, the number of concurrent lookups will be logged to
+  // UMA once the count has reached 0.
+  void DecrementLookupCount(const std::string& cache_key, bool should_log);
+
   // Inserts |session| into the cache at |cache_key|. If there is an existing
   // one, it is released. Every |expiration_check_count| calls, the cache is
   // checked for stale entries.
   void Insert(const std::string& cache_key, SSL_SESSION* session);
 
   // Removes all entries from the cache.
   void Flush();
 
   void SetClockForTesting(std::unique_ptr<base::Clock> clock);
 
   // Dumps memory allocation stats. |pmd| is the ProcessMemoryDump of the
   // browser process.
   void DumpMemoryStats(base::trace_event::ProcessMemoryDump* pmd);
 
  private:
+  struct Entry {
+   public:
+    Entry();
+    Entry(Entry&&);
+    ~Entry();
+
+    size_t active_lookups;
+    size_t max_lookups;
+    bool should_log;
+    bssl::UniquePtr<SSL_SESSION> session;
+  };
+
   // base::MemoryCoordinatorClient implementation:
   void OnMemoryStateChange(base::MemoryState state) override;
 
   // Returns true if |entry| is expired as of |now|.
   bool IsExpired(SSL_SESSION* session, time_t now);
 
   // Removes all expired sessions from the cache.
   void FlushExpiredSessions();
 
   // Clear cache on low memory notifications callback.
   void OnMemoryPressure(
       base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level);
 
   std::unique_ptr<base::Clock> clock_;
   Config config_;
-  base::HashingMRUCache<std::string, bssl::UniquePtr<SSL_SESSION>> cache_;
+  base::HashingMRUCache<std::string, Entry> cache_;
   size_t lookups_since_flush_;
 
   // TODO(davidben): After https://crbug.com/458365 is fixed, replace this with
   // a ThreadChecker. The session cache should be single-threaded like other
   // classes in net.
   base::Lock lock_;
 
   std::unique_ptr<base::MemoryPressureListener> memory_pressure_listener_;
 
   DISALLOW_COPY_AND_ASSIGN(SSLClientSessionCache);
 };
 
 }  // namespace net
 
 #endif  // NET_SSL_SSL_CLIENT_SESSION_CACHE_H_