[grid] Use a memoized config in most commands

This will allow us to configure the application once and share
implementations of classes between components without needing to rely
on nasty statics or traditionally implemented singletons.

java/server/src/org/openqa/selenium/grid/TemplateGridCommand.java

@@ -29,6 +29,7 @@
 import org.openqa.selenium.grid.config.ConfigFlags;
 import org.openqa.selenium.grid.config.EnvConfig;
 import org.openqa.selenium.grid.config.HasRoles;
+import org.openqa.selenium.grid.config.MemoizedConfig;
 import org.openqa.selenium.grid.log.LoggingOptions;
 import org.openqa.selenium.grid.server.HelpFlags;
 
@@ -81,7 +82,7 @@ public final Executable configure(PrintStream out, PrintStream err, String... ar
       allConfigs.add(configFlags.readConfigFiles());
       allConfigs.add(getDefaultConfig());
 
-      Config config = new CompoundConfig(allConfigs.toArray(new Config[0]));
+      Config config = new MemoizedConfig(new CompoundConfig(allConfigs.toArray(new Config[0])));
 
       if (configFlags.dumpConfig(config, out)) {
         return;

java/server/src/org/openqa/selenium/grid/config/MemoizedConfig.java

@@ -0,0 +1,140 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC 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.openqa.selenium.grid.config;
+
+import org.openqa.selenium.internal.Require;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicReference;
+
+public class MemoizedConfig implements Config {
+
+  private final Config delegate;
+
+  private final Map<Key, Optional<Boolean>> seenBools = new ConcurrentHashMap<>();
+  private final Map<Key, Object> seenClasses = new ConcurrentHashMap<>();
+  private final Map<Key, Optional<Integer>> seenInts = new ConcurrentHashMap<>();
+  private final Map<Key, Optional<String>> seenStrings = new ConcurrentHashMap<>();
+  private final Map<Key, Optional<List<String>>> seenOptions = new ConcurrentHashMap<>();
+
+  public MemoizedConfig(Config delegate) {
+    this.delegate = Require.nonNull("Delegate config", delegate);
+  }
+
+  @Override
+  public Set<String> getSectionNames() {
+    return delegate.getSectionNames();
+  }
+
+  @Override
+  public Set<String> getOptions(String section) {
+    Require.nonNull("Section name", section);
+    return delegate.getOptions(section);
+  }
+
+  @Override
+  public Optional<List<String>> getAll(String section, String option) {
+    Require.nonNull("Section name", section);
+    Require.nonNull("Option", option);
+
+    return seenOptions.computeIfAbsent(new Key(section, option), ignored -> delegate.getAll(section, option));
+  }
+
+  @Override
+  public Optional<String> get(String section, String option) {
+    Require.nonNull("Section name", section);
+    Require.nonNull("Option", option);
+
+    return seenStrings.computeIfAbsent(new Key(section, option), ignored -> delegate.get(section, option));
+  }
+
+  @Override
+  public Optional<Integer> getInt(String section, String option) {
+    Require.nonNull("Section name", section);
+    Require.nonNull("Option", option);
+
+    return seenInts.computeIfAbsent(new Key(section, option), ignored -> delegate.getInt(section, option));
+  }
+
+  @Override
+  public Optional<Boolean> getBool(String section, String option) {
+    Require.nonNull("Section name", section);
+    Require.nonNull("Option", option);
+
+    return seenBools.computeIfAbsent(new Key(section, option), ignored -> delegate.getBool(section, option));
+  }
+
+  @Override
+  public <X> X getClass(String section, String option, Class<X> typeOfX, String defaultClassName) {
+    Require.nonNull("Section name", section);
+    Require.nonNull("Option", option);
+    Require.nonNull("Type to load", typeOfX);
+    Require.nonNull("Default class name", defaultClassName);
+
+    AtomicReference<Exception> thrown = new AtomicReference<>();
+    Object value = seenClasses.computeIfAbsent(
+      new Key(section, option, typeOfX.toGenericString(), defaultClassName),
+      ignored -> {
+        try {
+          return delegate.getClass(section, option, typeOfX, defaultClassName);
+        } catch (Exception e) {
+          thrown.set(e);
+          return null;
+        }
+      });
+
+    if (value != null) {
+      return typeOfX.cast(value);
+    }
+
+    Exception exception = thrown.get();
+    if (exception instanceof RuntimeException) {
+      throw (RuntimeException) exception;
+    }
+    throw new ConfigException(exception);
+  }
+
+  private static class Key {
+    private final String[] segments;
+
+    public Key(String... segments) {
+      this.segments = segments;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+      if (!(o instanceof Key)) {
+        return false;
+      }
+      Key that = (Key) o;
+
+      return Arrays.equals(this.segments, that.segments);
+    }
+
+
+    @Override
+    public int hashCode() {
+      return Arrays.hashCode(segments);
+    }
+  }
+}