Mojo Log service and a thread-safe client library.

mojo/services/log/cpp/log_client.h

Index: mojo/services/log/cpp/log_client.h
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+// 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.
+
+// This is a client library that constructs a MojoLogger that can talk to a
+// Mojo logging service (see ../interfaces/log.mojo). It provides a |MojoLogger|
+// implementation which can be used as the default environment logger.
+//
+// Example application that uses this log client to talk to the log service:
+//
+//  class MyDelegate : public mojo::ApplicationDelegate {
+//   public:
+//    void Initialize(mojo::ApplicationImpl* app) override {
+//      LogPtr log;
+//      app->ConnectToService("mojo:log", &log);
+//      mojo::log::InitializeLogger(std::move(log),
+//                                  ApplicationRunner::GetDefaultLogger());
+//      mojo::ApplicationRunner::SetDefaultLogger(mojo::log::GetLogger());
+//    }
+//
+//    void Quit() {
+//      mojo::log::DestroyLogger();
+//    }
+//  };
+//
+//  MojoResult MojoMain(MojoHandle app_request) {
+//    mojo::ApplicationRunner runner(new MyDelegate);
+//    return runner.Run(app_request);
+//  }
+
+#ifndef MOJO_SERVICES_LOG_CPP_LOG_CLIENT_H_
+#define MOJO_SERVICES_LOG_CPP_LOG_CLIENT_H_
+
+#include "mojo/public/c/environment/logger.h"
+#include "mojo/services/log/interfaces/log.mojom.h"
+
+namespace mojo {
+namespace log {
+
+// Constructs a MojoLogger (which can be retrieved with |GetLogger()|) that
+// talks to the provided log service. |fallback_logger| must be non-null and
+// will be used if the provided |log_service| fails. The constructed MojoLogger
+// may also call into |fallback_logger|'s [Set|Get]MinimumLogLevel functions to
+// keep the minimum levels consistent.
+void InitializeLogger(LogPtr log_service, const MojoLogger* fallback_logger);
+
+// Must be called after |InitializeLogger()| and before |DestroyLogger()|. The
+// returned MojoLogger is thread-safe.
+const MojoLogger* GetLogger();
+
+void DestroyLogger();
+
+}  // namespace log
+}  // namespace mojo
+
+#endif  // MOJO_SERVICES_LOG_CPP_LOG_CLIENT_H_