shaded.com.google.errorprone.annotations.ThreadSafe Maven / Gradle / Ivy
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/*
* Copyright 2023 The Error Prone Authors.
*
* Licensed 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 shaded.shaded.com.google.errorprone.annotations;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Documented;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
/**
* This annotation indicates that the class/interface it is applied to is thread safe
*
* An object is thread safe if no sequences of accesses (like reads and writes to public fields
* or calls to public methods) may put the object into an invalid state, or cause it to violate its
* contract, regardless of the interleaving of those actions at runtime.
*
*
This annotation has two related-but-distinct purposes:
*
*
* - For humans: it indicates that the class/interface (and subclasses) is thread-safe
*
- For machines: it causes the annotated class/interface -- and all of its subtypes -- to be
* validated by the {@code shaded.shaded.com.google.errorprone.bugpatterns.threadsafety.ThreadSafeChecker}
* {@code BugChecker}.
*
*
* Note that passing the checks performed by the {@code ThreadSafeChecker} is neither necessary nor
* sufficient to guarantee the thread safety of a class. In fact, it is not possible to determine
* thread safety through static code analysis alone, and the goal of {@code ThreadSafeChecker} is to
* steer the code towards using standard thread-safe patterns, and then to assist the developer in
* avoiding common mistakes. It is not meant as a substitute for diligent code review by a
* knowledgeable developer.
*
* Also note that the only easy way to guarantee thread-safety of a class is to make it
* immutable, and you should do that whenever possible (or at the least, make as much of the class
* be immutable). Otherwise, writing a thread-safe class is inherently tricky and error prone, and
* keeping it thread-safe is even more so.
*
*
The remainder of this javadoc describes the heuristics enforced by {@code ThreadSafeChecker}
* and the related {@code shaded.shaded.com.google.errorprone.bugpatterns.threadsafety.GuardedByChecker} and
* {@code shaded.shaded.com.google.errorprone.bugpatterns.threadsafety.ImmutableChecker} on which the former
* relies.
*
*
The {@code ThreadSafeChecker} heuristics enforce that every field meets at least one of these
* requirements:
*
*
* - It is both {@code final} and its type is deemed inherently deeply thread-safe; and/or
*
- it is annotated with either {@link shaded.shaded.com.google.errorprone.annotations.concurrent.GuardedBy}
* (some other annotations named {@code GuardedBy} also work, though this the preferred);
*
*
* Below, more details about what is meant by "deemed inherently deeply thread-safe" are presented,
* and, afterwards, more about {@code GuardedBy}.
*
* A type is deemed inherently deeply thread-safe if it meets two requirements. The first
* requirement is that it meets at least one of these four conditions:
*
*
* - it is listed as a well-known immutable type in {@code
* shaded.shaded.com.google.errorprone.bugpatterns.threadsafety.WellKnownMutability} (e.g. a field of type
* {@link String}); and/or
*
- it is listed as a well-known thread-safe type in {@code
* shaded.shaded.com.google.errorprone.bugpatterns.threadsafety.WellKnownThreadSafety} (e.g. a field of type
* {@link java.util.concurrent.atomic.AtomicBoolean}); and/or
*
- it is annotated with {@link Immutable}; and/or
*
- it is annotated with {@link ThreadSafe}.
*
*
* This first requirement means the type is at least inherently shallowly thread-safe.
*
*
Fields annotated with {@code javax.annotation.concurrent.GuardedBy} are likely the meat of a
* mutable thread-safe class: these are things that need to be mutated, but should be done so in a
* safe manner -- i.e., (most likely) in critical sections of code that protect their access by
* means of a lock. See more information in that annotation's javadoc.
*
*
As stated before, the heuristics above are not sufficient to guarantee the thread safety of a
* class. Also as stated before, thread-safety is tricky, and requires diligent analysis by skilled
* people. That said, we provide here a few examples of common examples of ways to break these
* heuristics, so as to help you avoid them:
*
*
* - a non-private {@code @GuardedBy} field -- i.e.if a non-private {@code @GuardedBy} field is
* accessed outside the class, the code that enforces {@code @GuardedBy} will not prevent
* unprotected access and/or modifications to the field;
*
- indirect access to the field. There are several ways in which code may access the objects
* stored in the field indirectly (i.e. not directly referencing the field). In all these
* cases, {@code @GuardedBy} offers no enforcement. Here's some examples:
*
* - if the {@code @GuardedBy} field instance is part of an object by a method (e.g. a
* simple getter method or constructor parameter);
*
- if a method takes an out-parameter and the method calls a method in that
* out-parameter passing the instance of the {@code @GuardedBy} field, and that instance
* is stored in the out-parameter (i.e. a simple setter method);
*
* - methods that perform multiple operations -- e.g., if a class {@code Foo} contains a {@code
* AtomicInteger} (which is an inherently deeply thread-safe data structure), the following
* code makes this class not thread-safe:
*
{@code
* private void incrementMyAtomicInteger() {
* myAtomicInteger.set(myAtomicInteger.get() + 1);
* }
*
* }
*
*
* Also see https://errorprone.info/bugpattern/ThreadSafe
*/
// TODO(b/112275411): when fixed, delete the comment above about non-private fields
@Target({TYPE})
@Retention(RUNTIME)
// Note: besides abiding by the standard behavior of `@Inherited`, the behavior enforced by
// the static analysis effectively applies not only to classes that extend a class annotated with
// @ThreadSafe but *also* applies to classes that implement an annotated interface. This is because
// a class that implements an interface annotated with `@ThreadSafe` either: a. is anonymous, in
// which case the static analysis is implemented to run against it; or b. it is not anonymous, in
// which case the static analysis enforces that the class _also_ have an `@ThreadSafe` annotation.
@Inherited
@Documented
public @interface ThreadSafe {}