NotifyWithoutSynch.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>


<overview>
<p>The methods <code>notify</code>, <code>notifyAll</code>, and <code>wait</code>
 should only be called by a thread that is the owner of the object's monitor
 (intrinsic lock). In other words, the methods should only be called from within
 a synchronized statement or method. Otherwise the method call will throw
 <code>IllegalMonitorStateException</code>.
</p>

</overview>
<recommendation>

<p>Ensure that calls to <code>notify</code>, <code>notifyAll</code>,
 or <code>wait</code> are called from within a synchronized statement or method.
</p>

</recommendation>
<example>

<p>In the following example, the methods <code>produce</code> and <code>consume</code> use
<code>wait</code> and <code>notifyAll</code> to communicate. However, the <code>consume</code>
 method is not synchronized, so the calls to <code>wait</code> and <code>notifyAll</code> will
 always throw an exception.</p>

<sample src="NotifyWithoutSynch.java" />

<p>To fix this example, add the <code>synchronized</code> keyword to the
  declaration of the <code>consume</code> method.</p>

</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#notify()">Object.notify()</a>,
  <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#notifyAll()">Object.notifyAll()</a>,
  <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#wait()">Object.wait()</a>,
  <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#wait(long)">Object.wait(long)</a>.
</li>


</references>
</qhelp>