steveloughran commented on code in PR #6789: URL: https://github.com/apache/hadoop/pull/6789#discussion_r1666949043
########## hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/FlagSet.java: ########## @@ -0,0 +1,278 @@ +/* + * 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.hadoop.fs.impl; + +import java.util.Arrays; +import java.util.EnumSet; +import java.util.List; +import java.util.Map; +import java.util.Objects; +import java.util.Set; +import java.util.concurrent.atomic.AtomicBoolean; +import java.util.stream.Collectors; +import javax.annotation.Nullable; + +import org.apache.hadoop.conf.Configuration; +import org.apache.hadoop.fs.StreamCapabilities; +import org.apache.hadoop.util.ConfigurationHelper; +import org.apache.hadoop.util.Preconditions; + +import static org.apache.hadoop.util.ConfigurationHelper.mapEnumNamesToValues; + +/** + * A set of flags, constructed from a configuration option or from a string, + * with the semantics of + * {@link ConfigurationHelper#parseEnumSet(String, String, Class, boolean)} + * and implementing {@link StreamCapabilities}. + * <p> + * Thread safety: there is no synchronization on a mutable {@code FlagSet}. + * Once declared immutable, flags cannot be changed, so they + * becomes implicitly thread-safe. + */ +public final class FlagSet<E extends Enum<E>> implements StreamCapabilities { + + /** + * Set of flags. + */ + private final Set<E> flags; + + /** + * Is the set immutable? + */ + private final AtomicBoolean immutable = new AtomicBoolean(false); + + /** + * Mapping of prefixed flag names to enum values. + */ + private final Map<String, E> namesToValues; + + /** + * Create a FlagSet. + * @param enumClass class of enum + * @param prefix prefix (with trailing ".") for path capabilities probe + * @param flags flags. A copy of these are made. + */ + private FlagSet(final Class<E> enumClass, + final String prefix, + @Nullable final EnumSet<E> flags) { + + this.flags = flags != null + ? EnumSet.copyOf(flags) + : EnumSet.noneOf(enumClass); + this.namesToValues = mapEnumNamesToValues(prefix, enumClass); + } + + /** + * Get a copy of the flags. + * <p> + * This is immutable. + * @return the flags. + */ + public EnumSet<E> flags() { + return EnumSet.copyOf(flags); + } + + /** + * Probe for the FlagSet being empty. + * @return true if there are no flags set. + */ + public boolean isEmpty() { + return flags.isEmpty(); + } + + /** + * Is a flag enabled? + * @param flag flag to check + * @return true if it is in the set of enabled flags. + */ + public boolean enabled(final E flag) { + return flags.contains(flag); + } + + /** + * Check for mutability before any mutating operation. + * @throws IllegalStateException if the set is still mutable + */ + private void checkMutable() { + Preconditions.checkState(!immutable.get(), + "FlagSet is immutable"); + } + + /** + * Enable a flag. + * @param flag flag to enable. + */ + public void enable(final E flag) { + checkMutable(); + flags.add(flag); + } + + /** + * Disable a flag. + * @param flag flag to disable + */ + public void disable(final E flag) { + checkMutable(); + flags.remove(flag); + } + + /** + * Set a flag to the chosen value. + * @param flag flag + * @param state true to enable, false to disable. + */ + public void set(final E flag, boolean state) { + if (state) { + enable(flag); + } else { + disable(flag); + } + } + + /** + * Is a flag enabled? + * @param capability string to query the stream support for. + * @return true if the capability maps to an enum value and + * that value is set. + */ + @Override + public boolean hasCapability(final String capability) { + final E e = namesToValues.get(capability); + return e != null && enabled(e); + } + + /** + * Make immutable; no-op if already set. + */ + public void makeImmutable() { + immutable.set(true); + } + + @Override + public String toString() { + return "{" + + (flags.stream() + .map(e -> e.name()) + .collect(Collectors.joining(", "))) + + '}'; Review Comment: aren't curly braces the ones for set representations? also: https://xkcd.com/2954/ -- This is an automated message from the Apache Git Service. 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