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.
+
+#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 {
+
+// This is the client library that constructs a logger to talk to the Mojo
+// logging service (see ../interfaces/log.mojo).  It exposes a MojoLogger
+// interface for logging, which you may supply to your |mojo::Environment|.
+//
+// LogClient is only allowed to be instantiated once, and remain so for the
+// duration of its use.  The constructor will initialize some internal state and
+// take ownership of the supplied |log_service|.  If the pipe to the supplied
+// |log_service| fails, LogClient will fallback to the supplied
+// |fallback_logger|.
+//
+// This class is thread-safe.
+//
+// Example on how to replace the Environment's default logger with LogClient:
+//   LogPtr log_service;
+//   // .. bind log_service to proxy ..
+//   LogClient logclient(std::move(log_service),
+//                       Environment::GetDefaultLogger());
+//   Environment::SetDefaultLogger(LogClient::GetLogger());
+//   // At this point, |MOJO_LOG(..) <<| will start talking to the logging
+//      service.
+class LogClient {
+ public:
+  LogClient(LogPtr log_service, const MojoLogger* fallback_logger);
+  ~LogClient();
+
+  // You can retrieve the logger before any LogClient instance is created, but
+  // any uses of the logger may assert-fail.
+  static const MojoLogger* GetLogger();
+};
+
+}  // namespace log
+}  // namespace mojo
+
+#endif  // MOJO_SERVICES_LOG_CPP_LOG_CLIENT_H_