[GitHub] [cassandra] maedhroz commented on a change in pull request #1045: CASSANDRA-16663 Request-Based Native Transport Rate-Limiting

[GitBox <gi...@apache.org>]

maedhroz commented on a change in pull request #1045:
URL: https://github.com/apache/cassandra/pull/1045#discussion_r676792522



##########
File path: src/java/org/apache/cassandra/utils/NoWaitRateLimiter.java
##########
@@ -0,0 +1,261 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.cassandra.utils;
+
+import java.util.concurrent.TimeUnit;
+
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.NotThreadSafe;
+import javax.annotation.concurrent.ThreadSafe;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
+import com.google.common.base.Stopwatch;
+import com.google.common.base.Ticker;
+import com.google.common.math.LongMath;
+
+@ThreadSafe
+@SuppressWarnings("UnstableApiUsage")
+public class NoWaitRateLimiter
+{
+    @GuardedBy("this")
+    private Stopwatch stopwatch;
+
+    @GuardedBy("this")
+    private SmoothRateLimiter delegate;
+
+    private NoWaitRateLimiter(SmoothRateLimiter delegate, Ticker ticker)
+    {
+        this.delegate = delegate;
+        this.stopwatch = Stopwatch.createStarted(ticker);
+    }
+    
+    public static NoWaitRateLimiter create(double permitsPerSecond)
+    {
+        return create(permitsPerSecond, Ticker.systemTicker());
+    }
+
+    public static NoWaitRateLimiter create(double permitsPerSecond, Ticker ticker)
+    {
+        return create(permitsPerSecond, 1.0D, ticker);
+    }
+
+    public static NoWaitRateLimiter create(double permitsPerSecond, double burstSeconds)
+    {
+        return create(permitsPerSecond, burstSeconds, Ticker.systemTicker());
+    }
+
+    public static NoWaitRateLimiter create(double permitsPerSecond, double burstSeconds, Ticker ticker)
+    {
+        SmoothRateLimiter delegate = new SmoothRateLimiter(burstSeconds);
+        NoWaitRateLimiter limiter = new NoWaitRateLimiter(delegate, ticker);
+        limiter.setRate(permitsPerSecond);
+        return limiter;
+    }
+    
+    @VisibleForTesting
+    public synchronized void reset(double permitsPerSecond, double burstSeconds, Ticker ticker)
+    {
+        this.stopwatch = Stopwatch.createStarted(ticker);
+        this.delegate = new SmoothRateLimiter(burstSeconds);
+        setRate(permitsPerSecond);
+    }
+
+    public final void setRate(double permitsPerSecond) 
+    {
+        Preconditions.checkArgument(permitsPerSecond > 0.0D && !Double.isNaN(permitsPerSecond), "rate must be positive");
+        
+        synchronized (this) 
+        {
+            delegate.doSetRate(permitsPerSecond, stopwatch.elapsed(TimeUnit.MICROSECONDS));
+        }
+    }
+
+    public synchronized double getRate() 
+    {
+        return delegate.getRate();
+    }
+
+    /**
+     * Forces the acquisition of a single permit.
+     * 
+     * @return microseconds until the acquired permit is available, and zero if it already is
+     */
+    public synchronized long reserveAndGetWaitLength() 
+    {
+        long nowMicros = this.stopwatch.elapsed(TimeUnit.MICROSECONDS);
+        long momentAvailable = delegate.reserveEarliestAvailable(1, nowMicros);
+        return Math.max(momentAvailable - nowMicros, 0L);
+    }
+
+    public synchronized boolean tryAcquire()
+    {
+        long nowMicros = this.stopwatch.elapsed(TimeUnit.MICROSECONDS);
+
+        if (!delegate.canAcquire(nowMicros)) 
+        {
+            return false;
+        }
+
+        delegate.reserveEarliestAvailable(1, nowMicros);
+            
+        return true;
+    }
+
+    public synchronized boolean canAcquire() 
+    {
+        long nowMicros = this.stopwatch.elapsed(TimeUnit.MICROSECONDS);
+        return delegate.canAcquire(nowMicros);
+    }
+
+    public synchronized long waitTimeMicros()
+    {
+        long nowMicros = this.stopwatch.elapsed(TimeUnit.MICROSECONDS);
+        return delegate.waitTimeMicros(nowMicros);
+    }
+
+    @VisibleForTesting
+    public synchronized long getNextFreeTicketMicros()
+    {
+        return delegate.nextFreeTicketMicros;
+    }
+
+    public synchronized double getStoredPermits()
+    {
+        return delegate.getStoredPermits();
+    }
+    
+    @Override
+    public String toString()
+    {
+        return String.format("Maximum requests/second is %.2f. %.2f stored permits available.", 
+                             getRate(), getStoredPermits());
+    }
+
+    @NotThreadSafe
+    private static class SmoothRateLimiter
+    {
+        private double storedPermits;

Review comment:
       For reviewers, carrying the concept of stored permits into this was partially a consequence of copy/paste from the Guava `SmoothBursty` rate limiter in the initial prototype. It's possible that we really don't need this burst capability at all, especially in a first cut of this.
   
   ...and of course, before this commits/merges, we should probably determine whether any licensing matter needs to decorate `SmoothRateLimiter`, although the Guava rate limiter is Apache 2.0 licensed.
   
   CC @belliottsmith 




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