Use cache with weak keys in ChannelToEndpointChannel (#2367)

changelog/@unreleased/pr-2367.v2.yml

@@ -0,0 +1,5 @@
+type: feature
+feature:
+  description: Dialogue produces timer metrics for all endpoints.
+  links:
+  - https://github.com/palantir/dialogue/pull/2367

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

@@ -16,54 +16,25 @@
 
 package com.palantir.dialogue.core;
 
+import com.github.benmanes.caffeine.cache.Caffeine;
+import com.github.benmanes.caffeine.cache.LoadingCache;
 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 java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Function;
 
 final class ChannelToEndpointChannel implements Channel {
 
-    private final Function<Endpoint, Channel> adapter;
-    private final Map<Object, Channel> cache;
+    private final LoadingCache<Endpoint, Channel> cache;
 
-    ChannelToEndpointChannel(Function<Endpoint, Channel> adapter) {
-        this.adapter = adapter;
-        this.cache = new ConcurrentHashMap<>();
+    ChannelToEndpointChannel(Function<Endpoint, Channel> loader) {
+        this.cache = Caffeine.newBuilder().weakKeys().maximumSize(10_000).build(loader::apply);
     }
 
     @Override
     public ListenableFuture<Response> execute(Endpoint endpoint, Request request) {
-        return channelFor(endpoint).execute(endpoint, request);
-    }
-
-    private Channel channelFor(Endpoint endpoint) {
-        return cache.computeIfAbsent(key(endpoint), _key -> adapter.apply(endpoint));
-    }
-
-    /**
-     * Constant {@link Endpoint endpoints} may be safely used as cache keys, as opposed to dynamically created
-     * {@link Endpoint} objects which would result in a memory leak.
-     */
-    static boolean isConstant(Endpoint endpoint) {
-        // The conjure generator creates endpoints as enum values, which can safely be cached because they aren't
-        // dynamically created.
-        return endpoint instanceof Enum;
-    }
-
-    /**
-     * Creates a cache key for the given endpoint. Some consumers (CJR feign shim) may not use endpoint enums, so we
-     * cannot safely hold references to potentially short-lived objects. In such cases we use a string value based on
-     * the service-name endpoint-name tuple.
-     */
-    private static Object key(Endpoint endpoint) {
-        return isConstant(endpoint) ? endpoint : stringKey(endpoint);
-    }
-
-    private static String stringKey(Endpoint endpoint) {
-        return endpoint.serviceName() + '.' + endpoint.endpointName();
+        return cache.get(endpoint).execute(endpoint, request);
     }
 }

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

@@ -219,21 +219,25 @@ private static ImmutableList<LimitedChannel> createHostChannels(Config cf, List<
                                 .build());
                 channel = RetryOtherValidatingChannel.create(cf, channel);
                 channel = HostMetricsChannel.create(cf, channel, targetUri.uri());
-                Channel tracingChannel =
+                channel =
                         new TraceEnrichingChannel(channel, DialogueTracing.tracingTags(cf, uriIndexForInstrumentation));
-                channel = cf.isConcurrencyLimitingEnabled()
-                        ? new ChannelToEndpointChannel(endpoint -> {
-                            if (endpoint.tags().contains("dialogue-disable-endpoint-concurrency-limiting")) {
-                                return tracingChannel;
-                            }
-                            LimitedChannel limited = ConcurrencyLimitedChannel.createForEndpoint(
-                                    tracingChannel, cf.channelName(), uriIndexForInstrumentation, endpoint);
-                            return QueuedChannel.create(cf, endpoint, limited);
-                        })
-                        : tracingChannel;
-                LimitedChannel limitedChannel = cf.isConcurrencyLimitingEnabled()
-                        ? ConcurrencyLimitedChannel.createForHost(cf, channel, uriIndexForInstrumentation)
-                        : new ChannelToLimitedChannelAdapter(channel);
+
+                LimitedChannel limitedChannel;
+                if (cf.isConcurrencyLimitingEnabled()) {
+                    Channel unlimited = channel;
+                    channel = new ChannelToEndpointChannel(endpoint -> {
+                        if (endpoint.tags().contains("dialogue-disable-endpoint-concurrency-limiting")) {
+                            return unlimited;
+                        }
+                        LimitedChannel limited = ConcurrencyLimitedChannel.createForEndpoint(
+                                unlimited, cf.channelName(), uriIndexForInstrumentation, endpoint);
+                        return QueuedChannel.create(cf, endpoint, limited);
+                    });
+                    limitedChannel = ConcurrencyLimitedChannel.createForHost(cf, channel, uriIndexForInstrumentation);
+                } else {
+                    limitedChannel = new ChannelToLimitedChannelAdapter(channel);
+                }
+
                 perUriChannels.add(limitedChannel);
             }
             return perUriChannels.build();
@@ -253,11 +257,7 @@ private static EndpointChannelFactory createEndpointChannelFactory(Channel multi
                 channel = new RangeAcceptsIdentityEncodingChannel(channel);
                 channel = ContentEncodingChannel.of(channel, endpoint);
                 channel = TracedChannel.create(cf, channel, endpoint);
-                if (ChannelToEndpointChannel.isConstant(endpoint)) {
-                    // Avoid producing metrics for non-constant endpoints which may produce
-                    // high cardinality.
-                    channel = TimingEndpointChannel.create(cf, channel, endpoint);
-                }
+                channel = TimingEndpointChannel.create(cf, channel, endpoint);
                 channel = new RequestBodyValidationChannel(channel);
                 channel = new InterruptionChannel(channel);
                 return new NeverThrowEndpointChannel(channel); // this must come last as a defensive backstop