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https://issues.apache.org/jira/browse/HADOOP-19161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17864988#comment-17864988
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ASF GitHub Bot commented on HADOOP-19161:
-----------------------------------------
steveloughran commented on code in PR #6789:
URL: https://github.com/apache/hadoop/pull/6789#discussion_r1673756812
##########
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);
Review Comment:
you can dynamically update things as you go along (which is being done to
push that fs.s3a.create.performance flag in), then flip to being immutable
after which it is safe to pass across threads. I had thought about keeping it
permanently mutable and doing synchronized() on all changes, but felt this way
was more lightweight
> S3A: option "fs.s3a.performance.flags" to take list of performance flags
> ------------------------------------------------------------------------
>
> Key: HADOOP-19161
> URL: https://issues.apache.org/jira/browse/HADOOP-19161
> Project: Hadoop Common
> Issue Type: Improvement
> Components: fs/s3
> Affects Versions: 3.4.1
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Priority: Major
> Labels: pull-request-available
>
> HADOOP-19072 shows we want to add more optimisations than that of
> HADOOP-18930.
> * Extending the new optimisations to the existing option is brittle
> * Adding explicit options for each feature gets complext fast.
> Proposed
> * A new class S3APerformanceFlags keeps all the flags
> * it build this from a string[] of values, which can be extracted from
> getConf(),
> * and it can also support a "*" option to mean "everything"
> * this class can also be handed off to hasPathCapability() and do the right
> thing.
> Proposed optimisations
> * create file (we will hook up HADOOP-18930)
> * mkdir (HADOOP-19072)
> * delete (probe for parent path)
> * rename (probe for source path)
> We could think of more, with different names, later.
> The goal is make it possible to strip out every HTTP request we do for
> safety/posix compliance, so applications have the option of turning off what
> they don't need.
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