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| Fixes #XXXX. | ||
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| (Replace XXXX with the id of the issue fixed in this PR. Remove the above line if there is no corresponding | ||
| issue. Don't reference the issue in the title of this pull-request.) | ||
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| (If you are a committer, follow the PR action item checklist for committers: | ||
| https://github.com/apache/incubator-druid/blob/master/dev/committer-instructions.md#pr-and-issue-action-item-checklist-for-committers.) | ||
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| ### Description | ||
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| Describe the goal of this PR, what problem are you fixing. If there is a corresponding issue (referenced above), it's | ||
| not necessary to repeat the description here, however, you may choose to keep one summary sentence. | ||
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| Describe your patch: what did you change in code? How did you fix the problem? | ||
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| If there are several relatively logically separate changes in this PR, create a mini-section for each of them. For | ||
| example: | ||
| #### Fixed the bug ... | ||
| #### Renamed the class ... | ||
| #### Added a forbidden-apis entry ... | ||
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| In each section, please describe design decisions made, including: | ||
| - Choice of algorithms | ||
| - Behavioral aspects. What configuration values are acceptable? How are corner cases and error conditions handled, such | ||
| as when there are insufficient resources? | ||
| - Class organization and design (how the logic is split between classes, inheritance, composition, design patterns) | ||
| - Method organization and design (how the logic is split between methods, parameters and return types) | ||
| - Naming (class, method, API, configuration, HTTP endpoint, names of emitted metrics) | ||
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| It's good to describe an alternative design (or mention an alternative name) for every design (or naming) decision point | ||
| and compare the alternatives with the designs that you've implemented (or the names you've chosen) to highlight the | ||
| advantages of the chosen designs and names. | ||
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| If there was a discussion of the design of the feature implemented in this PR elsewhere (e. g. a "Proposal" issue, any | ||
| other issue, or a thread in the development mailing list), link to that discussion from this PR description and explain | ||
| what have changed in your final design compared to your original proposal or the consensus version in the end of the | ||
| discussion. If something hasn't changed since the original discussion, you can omit a detailed discussion of those | ||
| aspects of the design here, perhaps apart from brief mentioning for the sake of readability of this PR description. | ||
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| Some of the aspects mentioned above may be omitted for simple and small changes. | ||
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| <hr> | ||
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| This PR has: | ||
| - [ ] been self-reviewed. | ||
| - [ ] using the [concurrency checklist]( | ||
| https://github.com/apache/incubator-druid/blob/master/dev/code-review/concurrency.md) (Remove this item if the PR | ||
| doesn't have any relation to concurrency.) | ||
| - [ ] added documentation for new or modified features or behaviors. | ||
| - [ ] added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links. | ||
| - [ ] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar | ||
| reader. | ||
| - [ ] added unit tests or modified existing tests to cover new code paths. | ||
| - [ ] added integration tests. | ||
| - [ ] been tested in a test Druid cluster. | ||
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| Check the items by putting "x" in the brackets for the done things. Not all of these items apply to every PR. Remove the | ||
| items which are not done or not relevant to the PR. None of the items from the checklist above are strictly necessary, | ||
| but it would be very helpful if you at least self-review the PR. | ||
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| <hr> | ||
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| For reviewers: the key changed/added classes in this PR are `MyFoo`, `OurBar`, and `TheirBaz`. | ||
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| (Add this section in big PRs to ease navigation in them for reviewers.) |
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| <!-- | ||
| ~ 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. | ||
| --> | ||
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| ## Druid's Checklist for Concurrency Code | ||
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| Design | ||
| - [Concurrency is rationalized in the PR description?]( | ||
| https://github.com/code-review-checklists/java-concurrency#rationalize) | ||
| - [Can use patterns to simplify concurrency?](https://github.com/code-review-checklists/java-concurrency#use-patterns) | ||
| - Immutability/Snapshotting | ||
| - Divide and conquer | ||
| - Producer-consumer | ||
| - Instance confinement | ||
| - Thread/Task/Serial thread confinement | ||
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| Documentation | ||
| - [Thread-safety is justified in comments?]( | ||
| https://github.com/code-review-checklists/java-concurrency#justify-document) | ||
| - [Class (method, field) has concurrent access documentation?]( | ||
| https://github.com/code-review-checklists/java-concurrency#justify-document) | ||
| - [Threading model of a subsystem (class) is described?]( | ||
| https://github.com/code-review-checklists/java-concurrency#threading-flow-model) | ||
| - [Concurrent control flow (or data flow) of a subsystem (class) is described?]( | ||
| https://github.com/code-review-checklists/java-concurrency#threading-flow-model) | ||
| - [Class is documented as immutable, thread-safe, or not thread-safe?]( | ||
| https://github.com/code-review-checklists/java-concurrency#immutable-thread-safe) | ||
| - [Applied concurrency patterns are pronounced?]( | ||
| https://github.com/code-review-checklists/java-concurrency#name-patterns) | ||
| - [`@GuardedBy` annotation is used?](https://github.com/code-review-checklists/java-concurrency#guarded-by) | ||
| - [Safety of benign races is explained?]( | ||
| https://github.com/code-review-checklists/java-concurrency#document-benign-race) | ||
| - [Each use of `volatile` is justified?]( | ||
| https://github.com/code-review-checklists/java-concurrency#justify-volatile) | ||
| - [Field that is neither `volatile` nor annotated with `@GuardedBy` has a comment?]( | ||
| https://github.com/code-review-checklists/java-concurrency#plain-field) | ||
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| Excessive thread safety | ||
| - [No "extra" (pseudo) thread safety?](https://github.com/code-review-checklists/java-concurrency#pseudo-safety) | ||
| - [No atomics on which only `get()` and `set()` are called?]( | ||
| https://github.com/code-review-checklists/java-concurrency#redundant-atomics) | ||
| - [Class (method) needs to be thread-safe?]( | ||
| https://github.com/code-review-checklists/java-concurrency#unneeded-thread-safety) | ||
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| Race conditions | ||
| - [No `put()` or `remove()` calls on a `ConcurrentHashMap` after `get()` or `containsKey()`?]( | ||
| https://github.com/code-review-checklists/java-concurrency#chm-race) | ||
| - [No point accesses to a non-thread-safe collection outside of critical sections?]( | ||
| https://github.com/code-review-checklists/java-concurrency#unsafe-concurrent-point-read) | ||
| - [Iteration over a non-thread-safe collection doesn't leak outside of a critical section?]( | ||
| https://github.com/code-review-checklists/java-concurrency#unsafe-concurrent-iteration) | ||
| - [Non-trivial object is *not* returned from a getter in a thread-safe class?]( | ||
| https://github.com/code-review-checklists/java-concurrency#concurrent-mutation-race) | ||
| - [No separate getters to an atomically updated state?]( | ||
| https://github.com/code-review-checklists/java-concurrency#moving-state-race) | ||
| - [No state used for making decisions or preparing data inside a critical section is read outside?]( | ||
| https://github.com/code-review-checklists/java-concurrency#read-outside-critical-section-race) | ||
| - [No race conditions are possible between the program and users or other programs?]( | ||
| https://github.com/code-review-checklists/java-concurrency#outside-world-race) | ||
| - [No race conditions are possible on the file system?]( | ||
| https://github.com/code-review-checklists/java-concurrency#outside-world-race) | ||
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| Replacing locks with concurrency utilities | ||
| - [Can use `LifecycleLock` instead of a standard lock in a lifecycled object?](#use-lifecycle-lock) | ||
| - [Can use concurrency utility instead of `Object.wait()`/`notify()`?]( | ||
| https://github.com/code-review-checklists/java-concurrency#avoid-wait-notify) | ||
| - [Can use Guava’s `Monitor` instead of a standard lock with conditional waits?]( | ||
| https://github.com/code-review-checklists/java-concurrency#guava-monitor) | ||
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| Avoiding deadlocks | ||
| - [Can avoid nested critical sections?]( | ||
| https://github.com/code-review-checklists/java-concurrency#avoid-nested-critical-sections) | ||
| - [Locking order for nested critical sections is documented?]( | ||
| https://github.com/code-review-checklists/java-concurrency#document-locking-order) | ||
| - [Dynamically determined locks for nested critical sections are ordered?]( | ||
| https://github.com/code-review-checklists/java-concurrency#dynamic-lock-ordering) | ||
| - [No extension API calls within critical sections?]( | ||
| https://github.com/code-review-checklists/java-concurrency#non-open-call) | ||
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| Improving scalability | ||
| - [Critical section is as small as possible?]( | ||
| https://github.com/code-review-checklists/java-concurrency#minimize-critical-sections) | ||
| - [Can use `ConcurrentHashMap.compute()` or Guava's `Striped` for per-key locking?]( | ||
| https://github.com/code-review-checklists/java-concurrency#increase-locking-granularity) | ||
| - [Can replace blocking collection or a queue with a concurrent one?]( | ||
| https://github.com/code-review-checklists/java-concurrency#non-blocking-collections) | ||
| - [Can use `ClassValue` instead of `ConcurrentHashMap<Class, ...>`?]( | ||
| https://github.com/code-review-checklists/java-concurrency#use-class-value) | ||
| - [Considered `ReadWriteLock` (or `StampedLock`) instead of a simple lock?]( | ||
| https://github.com/code-review-checklists/java-concurrency#read-write-lock) | ||
| - [`StampedLock` is used instead of `ReadWriteLock` when reentrancy is not needed?]( | ||
| https://github.com/code-review-checklists/java-concurrency#use-stamped-lock) | ||
| - [Considered `LongAdder` instead of an `AtomicLong` for a "hot field"?]( | ||
| https://github.com/code-review-checklists/java-concurrency#long-adder-for-hot-fields) | ||
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| Lazy initialization and double-checked locking | ||
| - [Lazy initialization of a field should be thread-safe?]( | ||
| https://github.com/code-review-checklists/java-concurrency#lazy-init-thread-safety) | ||
| - [Considered double-checked locking for a lazy initialization to improve performance?]( | ||
| https://github.com/code-review-checklists/java-concurrency#use-dcl) | ||
| - [Considered eager initialization instead of a lazy initialization to simplify code?]( | ||
| https://github.com/code-review-checklists/java-concurrency#eager-init) | ||
| - [Double-checked locking follows the SafeLocalDCL pattern?]( | ||
| https://github.com/code-review-checklists/java-concurrency#safe-local-dcl) | ||
| - [Can do lazy initialization with a benign race and without locking to improve performance?]( | ||
| https://github.com/code-review-checklists/java-concurrency#lazy-init-benign-race) | ||
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| Non-blocking and partially blocking code | ||
| - [Non-blocking code has enough comments to make line-by-line checking as easy as possible?]( | ||
| https://github.com/code-review-checklists/java-concurrency#check-non-blocking-code) | ||
| - [Can use immutable POJO + compare-and-swap operations to simplify non-blocking code?]( | ||
| https://github.com/code-review-checklists/java-concurrency#swap-state-atomically) | ||
| - [Boundaries of non-blocking or benignly racy code are identified by WARNING comments?]( | ||
| https://github.com/code-review-checklists/java-concurrency#non-blocking-warning) | ||
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| Threads and Executors | ||
| - [Thread is named?](https://github.com/code-review-checklists/java-concurrency#name-threads) | ||
| - [Thread is daemon?](#daemon-threads) | ||
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There was a problem hiding this comment. There are three such links, they point to Druid specific items in the bottom of the page. |
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| - [Using `Execs` to create an `ExecutorService`?](#use-execs) | ||
| - [Can use `ExecutorService` instead of creating a new `Thread` each time some method is called?]( | ||
| https://github.com/code-review-checklists/java-concurrency#reuse-threads) | ||
| - [No network I/O in a CachedThreadPool?]( | ||
| https://github.com/code-review-checklists/java-concurrency#cached-thread-pool-no-io) | ||
| - [No blocking (incl. I/O) operations in a `ForkJoinPool` or in a parallel Stream pipeline? | ||
| ](https://github.com/code-review-checklists/java-concurrency#fjp-no-blocking) | ||
| - [Can execute non-blocking computation in `FJP.commonPool()` instead of a custom thread pool?]( | ||
| https://github.com/code-review-checklists/java-concurrency#use-common-fjp) | ||
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| Parallel Streams | ||
| - [Parallel Stream computation takes more than 100us in total?]( | ||
| https://github.com/code-review-checklists/java-concurrency#justify-parallel-stream-use) | ||
| - [Comment before a parallel Streams pipeline explains how it takes more than 100us in total?]( | ||
| https://github.com/code-review-checklists/java-concurrency#justify-parallel-stream-use) | ||
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| Thread interruption and `Future` cancellation | ||
| - [Interruption status is restored before propagating a wrapped `InterruptedException`? | ||
| ](https://github.com/code-review-checklists/java-concurrency#restore-interruption) | ||
| - [`InterruptedException` is swallowed only in the following kinds of methods? | ||
| ](https://github.com/code-review-checklists/java-concurrency#interruption-swallowing) | ||
| - `Runnable.run()`, `Callable.call()`, or methods to be passed to executors as lambda tasks | ||
| - Methods with "try" or "best effort" semantics | ||
| - [`InterruptedException` swallowing is documented for a method?]( | ||
| https://github.com/code-review-checklists/java-concurrency#interruption-swallowing) | ||
| - [Can use Guava's `Uninterruptibles` to avoid `InterruptedException` swallowing?]( | ||
| https://github.com/code-review-checklists/java-concurrency#interruption-swallowing) | ||
| - [`Future` is canceled upon catching an `InterruptedException` or a `TimeoutException` on `get()`?]( | ||
| https://github.com/code-review-checklists/java-concurrency#cancel-future) | ||
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| Time | ||
| - [`nanoTime()` values are compared in an overflow-aware manner?]( | ||
| https://github.com/code-review-checklists/java-concurrency#nano-time-overflow) | ||
| - [`currentTimeMillis()` is *not* used to measure time intervals and timeouts?]( | ||
| https://github.com/code-review-checklists/java-concurrency#time-going-backward) | ||
| - [Units for a time variable are identified in the variable's name or via `TimeUnit`?]( | ||
| https://github.com/code-review-checklists/java-concurrency#time-units) | ||
| - [Negative timeouts and delays are treated as zeros?]( | ||
| https://github.com/code-review-checklists/java-concurrency#treat-negative-timeout-as-zero) | ||
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| Thread safety of Cleaners and native code | ||
| - [`close()` is concurrently idempotent in a class with a `Cleaner` or `finalize()`?]( | ||
| https://github.com/code-review-checklists/java-concurrency#thread-safe-close-with-cleaner) | ||
| - [Method accessing native state calls `reachabilityFence()` in a class with a `Cleaner` or `finalize()`?]( | ||
| https://github.com/code-review-checklists/java-concurrency#reachability-fence) | ||
| - [`Cleaner` or `finalize()` is used for real cleanup, not mere reporting?]( | ||
| https://github.com/code-review-checklists/java-concurrency#finalize-misuse) | ||
| - [Considered making a class with native state thread-safe?]( | ||
| https://github.com/code-review-checklists/java-concurrency#thread-safe-native) | ||
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| <hr> | ||
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| <a name="use-lifecycle-lock"></a> | ||
| [#](#use-lifecycle-lock) Lk.D1. Is it possible to use Druid's `LifecycleLock` utility instead of a standard lock and | ||
| "started" flag in lifecycled objects with `start()` and `stop()` methods? See the Javadoc comment for `LifecycleLock` | ||
| for more details. | ||
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| <a name="daemon-threads"></a> | ||
| [#](#daemon-threads) TE.D1. Are Threads created directly or via a `ThreadFactory` configured to be daemon via | ||
| `setDaemon(true)`? Note that by default, ThreadFactories constructed via `Execs.makeThreadFactory()` methods create | ||
| daemon threads already. | ||
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| <a name="use-execs"></a> | ||
| [#](#use-execs) TE.D2. Is it possible to use one of the static factory methods in Druid's `Execs` utility class to | ||
| create an `ExecutorService` instead of Java's standard `ExecutorServices`? This is recommended because `Execs` configure | ||
| ThreadFactories to create daemon threads by default, as required by the previous item. | ||
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I think the wording on some of the checklist items could be made clearer, e.g.:
From that it's somewhat ambiguous as to which one is the positive recommendation, I think would be clearer if phrased as:
and for places with similar use of "aren't".