Add ThreadLogMessages and its test

util/thread/thread_log_messages.cc

+// Copyright 2015 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "util/thread/thread_log_messages.h"
+
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/threading/thread_local_storage.h"
+
+namespace crashpad {
+
+namespace {
+
+// While an object of this class exists, it will be set as the log message
+// handler. A thread may register its thread-specific log message list to
+// receive messages produced just on that thread.
+//
+// Only one object of this class may exist in the program at a time. There must
+// not be any log message handler in effect when it is created, and nothing else
+// can be set as a log message handler while an object of this class exists.
+//
+// Practically, the only object of this class that might exist is managed by the
+// g_master lazy instance, which will create it upon first use.
+class ThreadLogMessagesMaster {
+ public:
+  ThreadLogMessagesMaster() {
+    DCHECK(!tls_.initialized());
+    CHECK(tls_.Initialize(nullptr));
+
+    DCHECK(!logging::GetLogMessageHandler());
+    logging::SetLogMessageHandler(LogMessageHandler);
+  }
+
+  ~ThreadLogMessagesMaster() {
+    DCHECK_EQ(logging::GetLogMessageHandler(), LogMessageHandler);
+    logging::SetLogMessageHandler(nullptr);
+
+    tls_.Free();
+  }
+
+  void SetThreadMessageList(std::vector<std::string>* message_list) {
+    DCHECK_EQ(logging::GetLogMessageHandler(), LogMessageHandler);
+    DCHECK_NE(tls_.Get() != nullptr, message_list != nullptr);
+    tls_.Set(message_list);
+  }
+
+ private:
+  static bool LogMessageHandler(logging::LogSeverity severity,
+                                const char* file_path,
+                                int line,
+                                size_t message_start,
+                                const std::string& string) {
+    std::vector<std::string>* log_messages =
+        reinterpret_cast<std::vector<std::string>*>(tls_.Get());
+    if (log_messages) {
+      log_messages->push_back(string);
+    }
+
+    // Don’t consume the message. Allow it to be logged as if nothing was set as
+    // the log message handler.
+    return false;
+  }
+
+  static base::ThreadLocalStorage::StaticSlot tls_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThreadLogMessagesMaster);
+};
+
+// static
+base::ThreadLocalStorage::StaticSlot ThreadLogMessagesMaster::tls_
+    = TLS_INITIALIZER;
+
+base::LazyInstance<ThreadLogMessagesMaster>::Leaky g_master =
+    LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+ThreadLogMessages::ThreadLogMessages()
+    : log_messages_() {
+  g_master.Get().SetThreadMessageList(&log_messages_);
+}
+
+ThreadLogMessages::~ThreadLogMessages() {
+  g_master.Get().SetThreadMessageList(nullptr);
+}
+
+}  // namespace crashpad