WaitOutsideLoop.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>
<overview>
<p>Calling <code>Object.wait</code> outside of a loop may cause problems because the thread does
not go back to sleep after a spurious wake-up call. This results in the program continuing before 
the expected condition is met.
</p>

</overview>
<recommendation>

<p>Ensure that <code>wait</code> is called within a loop that tests for the condition that the 
thread is waiting for. This ensures that the program only proceeds to execute when the
relevant condition is true. Note that the thread that calls <code>wait</code> on an object must be
the owner of that object's monitor.
</p>

</recommendation>
<example>

<p>In the following example, <code>obj.wait</code> is called within a <code>while</code> loop
until the condition is true, at which point the program continues with the next statement after
the loop:</p>

<sample src="WaitOutsideLoop.java" />

</example>
<references>


    <li>J. Bloch, <em>Effective Java (second edition)</em>, p. 276. Addison-Wesley, 2008.</li>
    <li>Java API Specification: <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#wait()">Object.wait()</a>.</li>
    <li>The Java Tutorials: <a href="https://docs.oracle.com/javase/tutorial/essential/concurrency/guardmeth.html">Guarded Blocks</a>.</li>


</references>
</qhelp>