I see that the above annotations are used extensively in the book JCIP . I think it is really useful because even in the absence of proper documentation it says some things
These are custom annotations that are not part of the standard JDK. To be able to use them in your code, you need to add a dependency.
At jcip.net, there is a link to the library and its source in the bottom part of the page "Concurrency annotations: jar, javadoc, source".
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