Allow multiple logging::LogMessage{Handler,Listener}s

base/test/mock_log.cc

Index: base/test/mock_log.cc
diff --git a/base/test/mock_log.cc b/base/test/mock_log.cc
index a09000d8ed7f9e3080ff06a64cb060c76fa591f6..7e0531cfc4c37bce3597848dc5afe6ca9be7f280 100644
--- a/base/test/mock_log.cc
+++ b/base/test/mock_log.cc
@@ -2,14 +2,26 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "base/memory/ptr_util.h"
 #include "base/test/mock_log.h"
 
 namespace base {
 namespace test {
 
-// static
-MockLog* MockLog::g_instance_ = nullptr;
-Lock MockLog::g_lock;
+class MockLogMessageListener : logging::LogMessageListener {
+ public:
+  MockLogMessageListener(MockLog* mock_log) : mock_log_(mock_log) {}
+  void OnMessage(int severity,
+                 const char* file,
+                 int line,
+                 size_t message_start,
+                 const std::string& str) override {
+    return mock_log_->Log(severity, file, line, message_start, str);
+  }
+
+ private:
+  MockLog* mock_log_;
+};
 
 MockLog::MockLog() : is_capturing_logs_(false) {
 }
@@ -21,47 +33,23 @@ MockLog::~MockLog() {
 }
 
 void MockLog::StartCapturingLogs() {
-  AutoLock scoped_lock(g_lock);
-
   // We don't use CHECK(), which can generate a new LOG message, and
   // thus can confuse MockLog objects or other registered
   // LogSinks.
   RAW_CHECK(!is_capturing_logs_);
-  RAW_CHECK(!g_instance_);
 
   is_capturing_logs_ = true;
-  g_instance_ = this;
-  previous_handler_ = logging::GetLogMessageHandler();
-  logging::SetLogMessageHandler(LogMessageHandler);
+  listener_ = base::MakeUnique<MockLogMessageListener>(this);
 }
 
 void MockLog::StopCapturingLogs() {
-  AutoLock scoped_lock(g_lock);
-
   // We don't use CHECK(), which can generate a new LOG message, and
   // thus can confuse MockLog objects or other registered
   // LogSinks.
   RAW_CHECK(is_capturing_logs_);
-  RAW_CHECK(g_instance_ == this);
 
   is_capturing_logs_ = false;
-  logging::SetLogMessageHandler(previous_handler_);
-  g_instance_ = nullptr;
-}
-
-// static
-bool MockLog::LogMessageHandler(int severity,
-                                const char* file,
-                                int line,
-                                size_t message_start,
-                                const std::string& str) {
-  // gMock guarantees thread-safety for calling a mocked method
-  // (https://github.com/google/googlemock/blob/master/googlemock/docs/CookBook.md#using-google-mock-and-threads)
-  // but we also need to make sure that Start/StopCapturingLogs are synchronized
-  // with LogMessageHandler.
-  AutoLock scoped_lock(g_lock);
-
-  return g_instance_->Log(severity, file, line, message_start, str);
+  listener_.reset();
 }
 
 }  // namespace test