Add cluster state manager to manage cluster mode

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

sentinel-core/src/main/java/com/alibaba/csp/sentinel/cluster/ClusterStateManager.java

@@ -0,0 +1,185 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * 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.alibaba.csp.sentinel.cluster;
+
+import com.alibaba.csp.sentinel.cluster.client.ClusterTokenClient;
+import com.alibaba.csp.sentinel.cluster.client.TokenClientProvider;
+import com.alibaba.csp.sentinel.cluster.server.EmbeddedClusterTokenServer;
+import com.alibaba.csp.sentinel.cluster.server.EmbeddedClusterTokenServerProvider;
+import com.alibaba.csp.sentinel.init.InitExecutor;
+import com.alibaba.csp.sentinel.log.RecordLog;
+import com.alibaba.csp.sentinel.property.DynamicSentinelProperty;
+import com.alibaba.csp.sentinel.property.PropertyListener;
+import com.alibaba.csp.sentinel.property.SentinelProperty;
+import com.alibaba.csp.sentinel.util.TimeUtil;
+
+/**
+ * <p>Global tate manager for Sentinel cluster. This enables switching between cluster client and server.</p>
+ *
+ * @author Eric Zhao
+ * @since 1.4.0
+ */
+public final class ClusterStateManager {
+
+    public static final int CLUSTER_CLIENT = 0;
+    public static final int CLUSTER_SERVER = 1;
+
+    private static volatile int mode = -1;
+    private static volatile long lastModified = -1;
+
+    private static volatile SentinelProperty<Integer> stateProperty = new DynamicSentinelProperty<Integer>();
+    private static final PropertyListener<Integer> PROPERTY_LISTENER = new ClusterStatePropertyListener();
+
+    static {
+        InitExecutor.doInit();
+        stateProperty.addListener(PROPERTY_LISTENER);
+    }
+
+    public static void registerProperty(SentinelProperty<Integer> property) {
+        synchronized (PROPERTY_LISTENER) {
+            RecordLog.info("[ClusterStateManager] Registering new property to cluster state manager");
+            stateProperty.removeListener(PROPERTY_LISTENER);
+            property.addListener(PROPERTY_LISTENER);
+            stateProperty = property;
+        }
+    }
+
+    public static int getMode() {
+        return mode;
+    }
+
+    public static boolean isClient() {
+        return mode == CLUSTER_CLIENT;
+    }
+
+    public static boolean isServer() {
+        return mode == CLUSTER_SERVER;
+    }
+
+    /**
+     * <p>
+     * Set current mode to client mode. If Sentinel currently works in server mode,
+     * it will be turned off. Then the cluster client will be started.
+     * </p>
+     */
+    public static void setToClient() {
+        if (mode == CLUSTER_CLIENT) {
+            return;
+        }
+        mode = CLUSTER_CLIENT;
+        sleepIfNeeded();
+        lastModified = TimeUtil.currentTimeMillis();
+        try {
+            EmbeddedClusterTokenServer server = EmbeddedClusterTokenServerProvider.getServer();
+            if (server != null) {
+                server.stop();
+            }
+            ClusterTokenClient tokenClient = TokenClientProvider.getClient();
+            if (tokenClient != null) {
+                tokenClient.start();
+                RecordLog.info("[ClusterStateManager] Changing cluster mode to client");
+            } else {
+                RecordLog.warn("[ClusterStateManager] Cannot change to client (no client SPI found)");
+            }
+        } catch (Exception ex) {
+            RecordLog.warn("[ClusterStateManager] Error when changing cluster mode to client", ex);
+        }
+    }
+
+    /**
+     * <p>
+     * Set current mode to server mode. If Sentinel currently works in client mode,
+     * it will be turned off. Then the cluster server will be started.
+     * </p>
+     */
+    public static void setToServer() {
+        if (mode == CLUSTER_SERVER) {
+            return;
+        }
+        mode = CLUSTER_SERVER;
+        sleepIfNeeded();
+        lastModified = TimeUtil.currentTimeMillis();
+        try {
+            ClusterTokenClient tokenClient = TokenClientProvider.getClient();
+            if (tokenClient != null) {
+                tokenClient.stop();
+            }
+            EmbeddedClusterTokenServer server = EmbeddedClusterTokenServerProvider.getServer();
+            if (server != null) {
+                server.start();
+                RecordLog.info("[ClusterStateManager] Changing cluster mode to server");
+            } else {
+                RecordLog.warn("[ClusterStateManager] Cannot change to server (no server SPI found)");
+            }
+        } catch (Exception ex) {
+            RecordLog.warn("[ClusterStateManager] Error when changing cluster mode to server", ex);
+        }
+    }
+
+    /**
+     * The interval between two change operations should be greater than {@code MIN_INTERVAL} (by default 10s).
+     * Or we need to wait for a while.
+     */
+    private static void sleepIfNeeded() {
+        if (lastModified <= 0) {
+            return;
+        }
+        long now = TimeUtil.currentTimeMillis();
+        long durationPast = now - lastModified;
+        long estimated = durationPast - MIN_INTERVAL;
+        if (estimated < 0) {
+            try {
+                Thread.sleep(-estimated);
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+        }
+    }
+
+    public static long getLastModified() {
+        return lastModified;
+    }
+
+    private static class ClusterStatePropertyListener implements PropertyListener<Integer> {
+        @Override
+        public void configLoad(Integer value) {
+            applyState(value);
+        }
+
+        @Override
+        public void configUpdate(Integer value) {
+            applyState(value);
+        }
+
+        private synchronized void applyState(Integer state) {
+            if (state == null || state < 0) {
+                return;
+            }
+            switch (state) {
+                case CLUSTER_CLIENT:
+                    setToClient();
+                    break;
+                case CLUSTER_SERVER:
+                    setToServer();
+                    break;
+                default:
+                    RecordLog.warn("[ClusterStateManager] Ignoring unknown cluster state: " + state);
+            }
+        }
+    }
+
+    private static final int MIN_INTERVAL = 10 * 1000;
+}