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<p>
Class, field, and method level annotations for describing thread-safety policies.
</p>
<p>
Three class-level annotations describe the <em>intended</em> thread-safety promises of a class:
<code>@Immutable</code>, <code>@ThreadSafe</code>, and <code>@NotThreadSafe</code>.
<code>@Immutable</code> means that the class is immutable,
and implies <code>@ThreadSafe</code>.
<code>@NotThreadSafe</code> is optional;
if a class is not annotated as thread-safe, it should be presumed not to be
thread-safe, but if you want to make it extra clear, use
<code>@NotThreadSafe</code>.
</p>
<p>
These annotations are relatively unintrusive and are beneficial to
both users and maintainers. Users can see immediately whether a class
is thread-safe, and maintainers can see immediately whether
thread-safety guarantees must be preserved. Annotations are also
useful to a third constituency: tools. Static code-analysis tools may
be able to verify that the code complies with the contract indicated
by the annotation, such as verifying that a class annotated with
<code>@Immutable</code> actually is immutable.
</p>
<h2>Field and method annotations</h2>
<p>
The class-level annotations above are part of the public documentation
for the class. Other aspects of a class's thread-safety strategy are
entirely for maintainers and are not part of its public documentation.
</p>
<p>
Classes that use locking should document which state variables are
guarded with which locks, and which locks are used to guard those
variables. A common source of inadvertent non-thread-safety is when a
thread-safe class consistently uses locking to guard its state, but is
later modified to add either new state variables that are not
adequately guarded by locking, or new methods that do not use locking
properly to guard the existing state variables. Documenting which
variables are guarded by which locks can help prevent both types of
omissions.
</p>
<p>
The <code>@GuardedBy(lock)</code> annotation documents that a field or method should
be accessed only with a specific lock held.
</p>
<h2>Copyright and license</h2>
<p>
This software is copyright (c) 2005 Brian Goetz and Tim Peierls
and is released under the Creative Commons Attribution License
(http://creativecommons.org/licenses/by/2.5). The official home
for this software is http://www.jcip.net.
Any republication or derived work distributed in source code form
must include the copyright and license notice.
</p>
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