Make SSLClientSessionCacheOpenSSL thread-safe.

Although the network stack is single-threaded, it *should* be legal to spin up
a parallel instance of everything on another thread. Until
https://crbug.com/458365 is resolved, the session cache is one of the few
global mutable objects in the network stack, apart from test code. Thus it
needs to be locked.

BUG=476713

Review URL: https://codereview.chromium.org/1079943006

Cr-Commit-Position: refs/heads/master@{#325459}

net/ssl/ssl_client_session_cache_openssl.cc

@@ -6,7 +6,6 @@
 
 #include <utility>
 
-#include "base/logging.h"
 #include "base/time/clock.h"
 #include "base/time/default_clock.h"
 
@@ -20,11 +19,6 @@ SSLClientSessionCacheOpenSSL::SSLClientSessionCacheOpenSSL(const Config& config)
 }
 
 SSLClientSessionCacheOpenSSL::~SSLClientSessionCacheOpenSSL() {
-  // TODO(davidben): The session cache is currently a singleton, so it is
-  // destroyed on a different thread than the one it's created on. When
-  // https://crbug.com/458365 is fixed, this will no longer be an issue.
-  thread_checker_.DetachFromThread();
-
   Flush();
 }
 
@@ -34,7 +28,7 @@ size_t SSLClientSessionCacheOpenSSL::size() const {
 
 SSL_SESSION* SSLClientSessionCacheOpenSSL::Lookup(
     const std::string& cache_key) {
-  DCHECK(thread_checker_.CalledOnValidThread());
+  base::AutoLock lock(lock_);
 
   // Expire stale sessions.
   lookups_since_flush_++;
@@ -55,7 +49,7 @@ SSL_SESSION* SSLClientSessionCacheOpenSSL::Lookup(
 
 void SSLClientSessionCacheOpenSSL::Insert(const std::string& cache_key,
                                           SSL_SESSION* session) {
-  DCHECK(thread_checker_.CalledOnValidThread());
+  base::AutoLock lock(lock_);
 
   // Make a new entry.
   CacheEntry* entry = new CacheEntry;
@@ -67,15 +61,13 @@ void SSLClientSessionCacheOpenSSL::Insert(const std::string& cache_key,
 }
 
 void SSLClientSessionCacheOpenSSL::Flush() {
-  DCHECK(thread_checker_.CalledOnValidThread());
+  base::AutoLock lock(lock_);
 
   cache_.Clear();
 }
 
 void SSLClientSessionCacheOpenSSL::SetClockForTesting(
     scoped_ptr<base::Clock> clock) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
   clock_ = clock.Pass();
 }
 

net/ssl/ssl_client_session_cache_openssl.h

@@ -12,6 +12,7 @@
 #include "base/containers/mru_cache.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/synchronization/lock.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/time.h"
 #include "net/base/net_export.h"
@@ -82,7 +83,10 @@ class NET_EXPORT SSLClientSessionCacheOpenSSL {
   CacheEntryMap cache_;
   size_t lookups_since_flush_;
 
-  base::ThreadChecker thread_checker_;
+  // 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_;
 
   DISALLOW_COPY_AND_ASSIGN(SSLClientSessionCacheOpenSSL);
 };