feat: add local token cache for cluster

sentinel-cluster/sentinel-cluster-client-default/src/main/java/com/alibaba/csp/sentinel/cluster/client/DefaultClusterTokenClient.java

@@ -16,7 +16,13 @@
 package com.alibaba.csp.sentinel.cluster.client;
 
 import java.util.Collection;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
 
 import com.alibaba.csp.sentinel.cluster.ClusterConstants;
 import com.alibaba.csp.sentinel.cluster.ClusterErrorMessages;
@@ -35,6 +41,7 @@
 import com.alibaba.csp.sentinel.cluster.response.data.FlowTokenResponseData;
 import com.alibaba.csp.sentinel.log.RecordLog;
 import com.alibaba.csp.sentinel.util.StringUtil;
+import com.alibaba.csp.sentinel.concurrent.NamedThreadFactory;
 
 /**
  * Default implementation of {@link ClusterTokenClient}.
@@ -43,11 +50,30 @@
  * @since 1.4.0
  */
 public class DefaultClusterTokenClient implements ClusterTokenClient {
+    public class CachedTokenData {
+        AtomicInteger count;
+        AtomicInteger lastStatus;
+        AtomicLong lastWaitUntilMs;
+        AtomicInteger lastWaitPrefetchCnt;
+        AtomicInteger lastRemaining;
+        public CachedTokenData() {
+            count = new AtomicInteger(0);
+            lastStatus = new AtomicInteger(TokenResultStatus.OK);
+            lastWaitUntilMs = new AtomicLong(0);
+            lastWaitPrefetchCnt = new AtomicInteger(0);
+            lastRemaining = new AtomicInteger(0);
+        }
+    }
 
     private ClusterTransportClient transportClient;
     private TokenServerDescriptor serverDescriptor;
 
     private final AtomicBoolean shouldStart = new AtomicBoolean(false);
+    private int checkInterval = 2;
+    ConcurrentHashMap<Long, CachedTokenData> localPrefetchedTokens = new ConcurrentHashMap<>();
+    @SuppressWarnings("PMD.ThreadPoolCreationRule")
+    private final ScheduledExecutorService prefetchScheduler = Executors.newScheduledThreadPool(2,
+        new NamedThreadFactory("sentinel-cluster-prefetch-scheduler", true));
 
     public DefaultClusterTokenClient() {
         ClusterClientConfigManager.addServerChangeObserver(new ServerChangeObserver() {
@@ -146,6 +172,141 @@ public TokenServerDescriptor currentServer() {
         return serverDescriptor;
     }
 
+    public void setInterval(int val) {
+        checkInterval = val;
+    }
+
+    public void resetCache() {
+        localPrefetchedTokens.clear();
+    }
+
+    public int currentRuleCached(Long flowId) {
+        CachedTokenData d = localPrefetchedTokens.get(flowId);
+        if (d == null) {
+            return 0;
+        }
+        return d.count.get();
+    }
+
+    private void preFetch(Long flowId, CachedTokenData value, int prefetchCnt) {
+        long waitUntil = value.lastWaitUntilMs.get();
+        if (waitUntil > 0 && System.currentTimeMillis() < waitUntil) {
+            return;
+        }
+        if (waitUntil > 0) {
+            value.count.addAndGet(value.lastWaitPrefetchCnt.get());
+            value.lastStatus.set(TokenResultStatus.OK);
+            value.lastWaitUntilMs.set(0);
+            value.lastWaitPrefetchCnt.set(0);
+        }
+        int current = value.count.get();
+        if (current >= prefetchCnt / 2) {
+            return;
+        }
+        if (current < -1 * prefetchCnt) {
+            // avoid too much prefetch
+            current = -1 * prefetchCnt;
+        }
+        prefetchCnt = prefetchCnt - current;
+        TokenResult fetched = requestToken(flowId, prefetchCnt, true);
+        value.lastWaitUntilMs.set(0);
+        value.lastStatus.set(fetched.getStatus());
+        value.lastRemaining.set(fetched.getRemaining());
+        if (fetched.getStatus() == TokenResultStatus.OK) {
+            value.count.addAndGet(prefetchCnt);
+        } else if (fetched.getStatus() == TokenResultStatus.SHOULD_WAIT) {
+            value.lastWaitUntilMs.set(System.currentTimeMillis() + fetched.getWaitInMs());
+            value.lastWaitPrefetchCnt.set(prefetchCnt);
+        }
+    }
+
+    private TokenResult tryLocalCachedToken(CachedTokenData data, int acquireCount, int prefetchCnt) {
+        int count = data.count.get();
+        TokenResult ret = new TokenResult(data.lastStatus.get());
+        ret.setFromCached(true);
+        ret.setRemaining(data.lastRemaining.get());
+        if (count >= acquireCount) {
+            // here we allow the concurrency which may cause decrease to negative count, it
+            // is just skipped some requests
+            // and it will be refilled by the bg prefetch in next round.
+            data.count.addAndGet(-1 * acquireCount);
+            ret.setStatus(TokenResultStatus.OK);
+            return ret;
+        }
+        if (acquireCount > prefetchCnt) {
+            return null;
+        }
+        if (ret.getStatus() == TokenResultStatus.SHOULD_WAIT) {
+            int newN = data.count.addAndGet(-1 * acquireCount);
+            if (newN + data.lastWaitPrefetchCnt.get() < -1 * prefetchCnt) {
+                data.count.addAndGet(acquireCount);
+                if (acquireCount <= prefetchCnt / 2) {
+                    // since last status is still waiting, we should not block directly, make it failover to local
+                    ret.setStatus(TokenResultStatus.FAIL);
+                    return ret;
+                }
+                // for the large acquireCount, we can try remote again, since large request will
+                // much slower which will have less pressure to remote
+                return null;
+            }
+            int waitMs = (int) (data.lastWaitUntilMs.get() - System.currentTimeMillis());
+            if (waitMs > 0) {
+                ret.setWaitInMs(waitMs);
+            }
+            return ret;
+        } else if (ret.getStatus() == TokenResultStatus.OK) {
+            // last ok, but the cached count is not enough, we can preuse it to avoid remote
+            // request too often,
+            // otherwise just try remote request
+            int newN = data.count.addAndGet(-1 * acquireCount);
+            if (newN < -1 * prefetchCnt * 2) {
+                // preuse failed since not enough, added it back
+                data.count.addAndGet(acquireCount);
+                if (acquireCount <= prefetchCnt / 2) {
+                    // since last is still ok, we should not block directly, make it failover to local
+                    ret.setStatus(TokenResultStatus.FAIL);
+                    return ret;
+                }
+                // for the large acquireCount, we can try remote again, since large request will much slower which will have less pressure to remote
+                return null;
+            }
+            // preuse ok
+            return ret;
+        } else {
+            // should fail directly
+            return ret;
+        }
+    }
+
+    @Override
+    public TokenResult requestTokenWithCache(Long flowId, int acquireCount, int prefetchCnt) {
+        if (notValidRequest(flowId, acquireCount)) {
+            return badRequest();
+        }
+        // try local prefetched first
+        CachedTokenData data = localPrefetchedTokens.get(flowId);
+        if (data != null) {
+            TokenResult ret = tryLocalCachedToken(data, acquireCount, prefetchCnt);
+            if (ret != null) {
+                return ret;
+            }
+        } else {
+            localPrefetchedTokens.computeIfAbsent(flowId, k -> {
+                CachedTokenData v = new CachedTokenData();
+                prefetchScheduler.scheduleAtFixedRate(() -> {
+                    try {
+                        preFetch(flowId, v, prefetchCnt);
+                    } catch (Throwable e) {
+                        RecordLog.info("[DefaultClusterTokenClient] prefetch failed for flowId {}", flowId, e);
+                    }
+                }, 0, checkInterval, TimeUnit.MILLISECONDS);
+                return v;
+            });
+        }
+        // fallback to remote request
+        return requestToken(flowId, acquireCount, true);
+    }
+
     @Override
     public TokenResult requestToken(Long flowId, int acquireCount, boolean prioritized) {
         if (notValidRequest(flowId, acquireCount)) {