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

net/ssl/ssl_client_session_cache.cc

Index: net/ssl/ssl_client_session_cache.cc
diff --git a/net/ssl/ssl_client_session_cache.cc b/net/ssl/ssl_client_session_cache.cc
index 19b9d556a13c9c0c2f9d15f00a835f44254ba2e1..52e7ac26369ac4688e95f1660e74ca64d6b0cba2 100644
--- a/net/ssl/ssl_client_session_cache.cc
+++ b/net/ssl/ssl_client_session_cache.cc
@@ -7,6 +7,7 @@
 #include <utility>
 
 #include "base/memory/memory_coordinator_client_registry.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/stringprintf.h"
 #include "base/time/clock.h"
 #include "base/time/default_clock.h"
@@ -17,6 +18,11 @@
 
 namespace net {
 
+SSLClientSessionCache::Entry::Entry()
+    : active_lookups(0), max_lookups(0), should_log(false) {}
+SSLClientSessionCache::Entry::Entry(Entry&&) = default;
+SSLClientSessionCache::Entry::~Entry() = default;
+
 SSLClientSessionCache::SSLClientSessionCache(const Config& config)
     : clock_(new base::DefaultClock),
       config_(config),
@@ -51,22 +57,53 @@ bssl::UniquePtr<SSL_SESSION> SSLClientSessionCache::Lookup(
   if (iter == cache_.end())
     return nullptr;
 
-  SSL_SESSION* session = iter->second.get();
+  SSL_SESSION* session = iter->second.session.get();
   if (IsExpired(session, clock_->Now().ToTimeT())) {
     cache_.Erase(iter);
     return nullptr;
   }
 
+  iter->second.active_lookups++;
+  if (iter->second.active_lookups > iter->second.max_lookups)
+    iter->second.max_lookups = iter->second.active_lookups;
+
   SSL_SESSION_up_ref(session);
   return bssl::UniquePtr<SSL_SESSION>(session);
 }
 
+void SSLClientSessionCache::DecrementLookupCount(const std::string& cache_key,
+                                                 bool should_log) {
+  base::AutoLock lock(lock_);
+
+  // It's possible that the cached session for this key was deleted after the
+  // Lookup, and also possible that it has been replaced by a new Entry. If
+  // that's the case, don't do anything.
+  auto iter = cache_.Get(cache_key);
+  if (iter == cache_.end() || iter->second.active_lookups == 0)
+    return;
+
+  iter->second.active_lookups--;
+  if (should_log)
+    iter->second.should_log = true;
+
+  if (iter->second.active_lookups == 0) {
+    if (iter->second.should_log) {
+      UMA_HISTOGRAM_EXACT_LINEAR("Net.SSLSessionConcurrentLookupCount",
+                                 iter->second.max_lookups, 20);
+    }
+    iter->second.max_lookups = 0;
+    iter->second.should_log = false;
+  }
+}
+
 void SSLClientSessionCache::Insert(const std::string& cache_key,
                                    SSL_SESSION* session) {
   base::AutoLock lock(lock_);
 
   SSL_SESSION_up_ref(session);
-  cache_.Put(cache_key, bssl::UniquePtr<SSL_SESSION>(session));
+  Entry entry;
+  entry.session = bssl::UniquePtr<SSL_SESSION>(session);
+  cache_.Put(cache_key, std::move(entry));
 }
 
 void SSLClientSessionCache::Flush() {
@@ -101,7 +138,7 @@ void SSLClientSessionCache::DumpMemoryStats(
   int total_serialized_cert_size = 0;
   int total_cert_count = 0;
   for (const auto& pair : cache_) {
-    auto entry = pair.second.get();
+    auto entry = pair.second.session.get();
     auto cert_chain = entry->x509_chain;
     size_t cert_count = sk_X509_num(cert_chain);
     total_cert_count += cert_count;
@@ -128,7 +165,7 @@ void SSLClientSessionCache::FlushExpiredSessions() {
   time_t now = clock_->Now().ToTimeT();
   auto iter = cache_.begin();
   while (iter != cache_.end()) {
-    if (IsExpired(iter->second.get(), now)) {
+    if (IsExpired(iter->second.session.get(), now)) {
       iter = cache_.Erase(iter);
     } else {
       ++iter;