fix #351 fix #302 fix #312 Replace QueuedChannel with a backoff based retryer

changelog/@unreleased/pr-432.v2.yml

@@ -0,0 +1,5 @@
+type: improvement
+improvement:
+  description: Replace QueuedChannel with a backoff based retryer
+  links:
+  - https://github.com/palantir/dialogue/pull/432

dialogue-core/src/main/java/com/palantir/dialogue/core/LimitedChannelListener.java → dialogue-core/src/main/java/com/palantir/dialogue/core/BackoffStrategy.java

@@ -13,17 +13,14 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package com.palantir.dialogue.core;
 
-@FunctionalInterface
-interface LimitedChannelListener {
+import java.time.Duration;
+
+/** Defines a strategy for waiting in between successive retries of an operation that is subject to failure. */
+interface BackoffStrategy {
 
-    /**
-     * Invoked when requests may succeed. There is no guarantee that requests will be accepted.
-     * This is only necessary if edge-triggering is not sufficient. For example if permits are based
-     * on the number of active requests, when existing requests complete this is triggered automatically.
-     * LimitedChannel implementations <i>should</i> invoke {@link #onChannelReady()} when another
-     * event (scheduled timeout) allows requests to proceed.
-     */
-    void onChannelReady();
+    /** Returns the next suggested backoff duration. */
+    Duration backoffDuration(int failures);
 }

dialogue-core/src/main/java/com/palantir/dialogue/core/BlacklistingChannel.java

@@ -18,24 +18,17 @@
 
 import com.github.benmanes.caffeine.cache.Ticker;
 import com.google.common.annotations.VisibleForTesting;
-import com.google.common.base.Suppliers;
 import com.google.common.util.concurrent.FutureCallback;
 import com.google.common.util.concurrent.ListenableFuture;
-import com.google.common.util.concurrent.ThreadFactoryBuilder;
 import com.palantir.dialogue.Endpoint;
 import com.palantir.dialogue.Request;
 import com.palantir.dialogue.Response;
 import com.palantir.logsafe.SafeArg;
 import com.palantir.logsafe.UnsafeArg;
 import java.time.Duration;
 import java.util.Optional;
-import java.util.concurrent.Executors;
-import java.util.concurrent.ScheduledExecutorService;
-import java.util.concurrent.ScheduledFuture;
-import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
-import java.util.function.Supplier;
 import javax.annotation.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -53,45 +46,21 @@ final class BlacklistingChannel implements LimitedChannel {
 
     private static final Logger log = LoggerFactory.getLogger(BlacklistingChannel.class);
     private static final int NUM_PROBATION_REQUESTS = 5;
-    /*
-     * Shared single thread executor is reused between all blacklisting channels. If it becomes oversaturated
-     * we may wait longer than expected before resuming requests to blacklisted channels, but this is an
-     * edge case where things are already operating in a degraded state.
-     */
-    private static final Supplier<ScheduledExecutorService> sharedScheduler = Suppliers.memoize(
-            () -> Executors.newSingleThreadScheduledExecutor(new ThreadFactoryBuilder()
-                    .setNameFormat("dialogue-BlacklistingChannel-scheduler-%d")
-                    .setDaemon(false)
-                    .build()));
 
     private final LimitedChannel delegate;
     private final Duration duration;
     private final Ticker ticker;
-    private final LimitedChannelListener listener;
-    private final ScheduledExecutorService scheduler;
     private final AtomicReference<BlacklistState> channelBlacklistState;
 
-    BlacklistingChannel(LimitedChannel delegate, Duration duration, LimitedChannelListener listener) {
-        this(delegate, duration, listener, Ticker.systemTicker(), sharedScheduler.get());
+    BlacklistingChannel(LimitedChannel delegate, Duration duration) {
+        this(delegate, duration, Ticker.systemTicker());
     }
 
     @VisibleForTesting
-    BlacklistingChannel(LimitedChannel delegate, Duration duration, LimitedChannelListener listener, Ticker ticker) {
-        this(delegate, duration, listener, ticker, sharedScheduler.get());
-    }
-
-    @VisibleForTesting
-    BlacklistingChannel(
-            LimitedChannel delegate,
-            Duration duration,
-            LimitedChannelListener listener,
-            Ticker ticker,
-            ScheduledExecutorService scheduler) {
+    BlacklistingChannel(LimitedChannel delegate, Duration duration, Ticker ticker) {
         this.delegate = delegate;
         this.duration = duration;
         this.ticker = ticker;
-        this.listener = listener;
-        this.scheduler = scheduler;
         this.channelBlacklistState = new AtomicReference<>();
     }
 
@@ -112,15 +81,12 @@ public String toString() {
 
     private final class BlacklistState {
         private final AtomicReference<Probation> probation = new AtomicReference<>();
-        private final ScheduledFuture<?> scheduledFuture;
         private final long blacklistUntilNanos;
         private final int probationPermits;
 
         BlacklistState(Duration duration, int probationPermits) {
             this.blacklistUntilNanos = ticker.read() + duration.toNanos();
             this.probationPermits = probationPermits;
-            this.scheduledFuture =
-                    scheduler.schedule(this::maybeBeginProbation, duration.toNanos(), TimeUnit.NANOSECONDS);
         }
 
         Optional<ListenableFuture<Response>> maybeExecute(Endpoint endpoint, Request request) {
@@ -148,8 +114,6 @@ Optional<Probation> maybeBeginProbation() {
                     if (log.isDebugEnabled()) {
                         log.debug("Channel {} is entering probation", UnsafeArg.of("channel", delegate));
                     }
-                    listener.onChannelReady();
-                    scheduledFuture.cancel(false);
                 }
                 return Optional.ofNullable(probation.get());
             }
@@ -161,7 +125,7 @@ void markSuccess() {
             if (maybeProbation != null && maybeProbation.checkIfProbationIsComplete()) {
                 log.debug("Clearing probation state");
                 if (channelBlacklistState.compareAndSet(this, null)) {
-                    listener.onChannelReady();
+                    log.debug("Channel is no longer blacklisted");
                 } else {
                     log.debug("Blacklist state has already been updated");
                 }

dialogue-core/src/main/java/com/palantir/dialogue/core/LimitedChannelAdapter.java → dialogue-core/src/main/java/com/palantir/dialogue/core/ChannelToLimitedChannelAdapter.java

@@ -24,11 +24,11 @@
 import java.util.Optional;
 
 /** Adapter from {@link Channel} to {@link LimitedChannel} which always returns a {@link Optional#isPresent() value}. */
-final class LimitedChannelAdapter implements LimitedChannel {
+final class ChannelToLimitedChannelAdapter implements LimitedChannel {
 
     private final Channel delegate;
 
-    LimitedChannelAdapter(Channel delegate) {
+    ChannelToLimitedChannelAdapter(Channel delegate) {
         this.delegate = Preconditions.checkNotNull(delegate, "Channel");
     }
 
@@ -39,6 +39,6 @@ public Optional<ListenableFuture<Response>> maybeExecute(Endpoint endpoint, Requ
 
     @Override
     public String toString() {
-        return "LimitedChannelAdapter{delegate=" + delegate + '}';
+        return "ChannelToLimitedChannelAdapter{delegate=" + delegate + '}';
     }
 }

dialogue-core/src/main/java/com/palantir/dialogue/core/Channels.java

@@ -26,7 +26,6 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.function.Function;
-import javax.annotation.Nullable;
 
 public final class Channels {
 
@@ -39,26 +38,24 @@ public static Channel create(Collection<? extends Channel> channels, ClientConfi
         Preconditions.checkArgument(config.userAgent().isPresent(), "config.userAgent() must be specified");
 
         DialogueClientMetrics clientMetrics = DialogueClientMetrics.of(config.taggedMetricRegistry());
-        // n.b. This becomes cleaner once we support reloadable channels, the queue can be created first, and
-        // each limited channel can be created later and passed a method reference to the queued channel.
-        DeferredLimitedChannelListener queueListener = new DeferredLimitedChannelListener();
         List<LimitedChannel> limitedChannels = channels.stream()
                 // Instrument inner-most channel with metrics so that we measure only the over-the-wire-time
                 .map(channel -> new InstrumentedChannel(channel, clientMetrics))
                 // TracedChannel must wrap TracedRequestChannel to ensure requests have tracing headers.
                 .map(TracedRequestChannel::new)
                 .map(channel -> new TracedChannel(channel, "Dialogue-http-request"))
-                .map(LimitedChannelAdapter::new)
+                .map(ChannelToLimitedChannelAdapter::new)
                 .map(concurrencyLimiter(config, clientMetrics))
                 .map(channel -> new FixedLimitedChannel(channel, MAX_REQUESTS_PER_CHANNEL, clientMetrics))
                 .collect(ImmutableList.toImmutableList());
 
         LimitedChannel limited = nodeSelectionStrategy(config, limitedChannels);
-        QueuedChannel queuedChannel = new QueuedChannel(limited, DispatcherMetrics.of(config.taggedMetricRegistry()));
-        queueListener.delegate = queuedChannel::schedule;
-        Channel channel = queuedChannel;
+        Channel channel = new LimitedChannelToChannelAdapter(limited);
         channel = new TracedChannel(channel, "Dialogue-request-attempt");
-        channel = new RetryingChannel(channel, config.maxNumRetries(), config.serverQoS());
+        if (config.maxNumRetries() > 0) {
+            channel =
+                    new RetryingChannel(channel, config.maxNumRetries(), config.backoffSlotSize(), config.serverQoS());
+        }
         channel = new UserAgentChannel(channel, config.userAgent().get());
         channel = new DeprecationWarningChannel(channel, clientMetrics);
         channel = new ContentDecodingChannel(channel);
@@ -97,15 +94,4 @@ private static Function<LimitedChannel, LimitedChannel> concurrencyLimiter(
         throw new SafeIllegalStateException(
                 "Encountered unknown client QoS configuration", SafeArg.of("ClientQoS", clientQoS));
     }
-
-    private static final class DeferredLimitedChannelListener implements LimitedChannelListener {
-        @Nullable
-        private LimitedChannelListener delegate;
-
-        @Override
-        public void onChannelReady() {
-            Preconditions.checkNotNull(delegate, "Delegate listener has not been initialized")
-                    .onChannelReady();
-        }
-    }
 }

dialogue-core/src/main/java/com/palantir/dialogue/core/ExponentialBackoffStrategy.java

@@ -0,0 +1,40 @@
+/*
+ * (c) Copyright 2020 Palantir Technologies Inc. All rights reserved.
+ *
+ * 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.palantir.dialogue.core;
+
+import java.time.Duration;
+import java.util.function.DoubleSupplier;
+
+final class ExponentialBackoffStrategy implements BackoffStrategy {
+
+    private final Duration backoffSlotSize;
+    private final DoubleSupplier random;
+
+    ExponentialBackoffStrategy(Duration backoffSlotSize, DoubleSupplier random) {
+        this.backoffSlotSize = backoffSlotSize;
+        this.random = random;
+    }
+
+    @Override
+    public Duration backoffDuration(int failures) {
+        if (failures == 0) {
+            return Duration.ZERO;
+        }
+        int upperBound = (int) Math.pow(2, failures - 1);
+        return Duration.ofNanos(Math.round(backoffSlotSize.toNanos() * random.getAsDouble() * upperBound));
+    }
+}

dialogue-core/src/main/java/com/palantir/dialogue/core/LimitedChannel.java

@@ -26,9 +26,6 @@
  * Similar to {@link com.palantir.dialogue.Channel}, but may not actually execute the call (eg: when the channel is
  * overloaded). Semantics match {@link com.palantir.dialogue.Channel} aside from returning an
  * {@link Optional optional response}.
- * Limited channels must limit exclusively based on the state of the {@link com.palantir.dialogue.Channel}, not
- * the {@link Endpoint} or {@link Request} arguments, otherwise the caller (generally a {@link QueuedChannel})
- * may prevent <i>all</i> requests from proceeding.
  */
 interface LimitedChannel {
     Optional<ListenableFuture<Response>> maybeExecute(Endpoint endpoint, Request request);

dialogue-core/src/main/java/com/palantir/dialogue/core/LimitedChannelToChannelAdapter.java

@@ -0,0 +1,51 @@
+/*
+ * (c) Copyright 2020 Palantir Technologies Inc. All rights reserved.
+ *
+ * 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.palantir.dialogue.core;
+
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
+import com.palantir.dialogue.Channel;
+import com.palantir.dialogue.Endpoint;
+import com.palantir.dialogue.Request;
+import com.palantir.dialogue.Response;
+import com.palantir.logsafe.Preconditions;
+import com.palantir.logsafe.exceptions.SafeRuntimeException;
+import java.util.function.Supplier;
+
+/** Adapter from {@link LimitedChannel} to {@link Channel} which produces a failed future when results are limited. */
+final class LimitedChannelToChannelAdapter implements Channel {
+
+    // Avoid method reference allocations
+    @SuppressWarnings("UnnecessaryLambda")
+    private static final Supplier<ListenableFuture<Response>> limitedResultSupplier =
+            () -> Futures.immediateFailedFuture(new SafeRuntimeException("Failed to make a request"));
+
+    private final LimitedChannel delegate;
+
+    LimitedChannelToChannelAdapter(LimitedChannel delegate) {
+        this.delegate = Preconditions.checkNotNull(delegate, "LimitedChannel");
+    }
+
+    @Override
+    public ListenableFuture<Response> execute(Endpoint endpoint, Request request) {
+        return delegate.maybeExecute(endpoint, request).orElseGet(limitedResultSupplier);
+    }
+
+    @Override
+    public String toString() {
+        return "LimitedChannelToChannelAdapter{delegate=" + delegate + '}';
+    }
+}