Export ServerInformation to extensions and plugins

Plugins can take this value by injection and learn the current
server state during their own LifecycleListener. This enables a
plugin to determine if it is loading as part of server startup, or
because it was dynamically installed or reloaded by an administrator.

Change-Id: Iac57e039ed9f9f3ecaf2f384c5a3c6a66223f5e1

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/systemstatus/ServerInformation.java

@@ -0,0 +1,42 @@
+// Copyright (C) 2012 The Android Open Source Project
+//
+// 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.
+
+package com.google.gerrit.extensions.systemstatus;
+
+/** Exports current server information to an extension. */
+public interface ServerInformation {
+  /** Current state of the server. */
+  public enum State {
+    /**
+     * The server is starting up, and network connections are not yet being
+     * accepted. Plugins or extensions starting during this time are starting
+     * for the first time in this process.
+     */
+    STARTUP,
+
+    /**
+     * The server is running and handling requests. Plugins starting during this
+     * state may be reloading, or being installed into a running system.
+     */
+    RUNNING,
+
+    /**
+     * The server is attempting a graceful halt of operations and will exit (or
+     * be killed by the operating system) soon.
+     */
+    SHUTDOWN;
+  }
+
+  State getState();
+}