CallsToRunnableRun.qhelp

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


<overview>
<p>A direct call of a <code>Thread</code> object's <code>run</code> method
does not start a separate thread. The method is executed within the current thread.
This is an unusual use because <code>Thread.run()</code> is normally 
intended to be called from within a separate thread. 
</p>

</overview>
<recommendation>

<p>To execute <code>Runnable.run</code> from within a separate thread, do one of the 
following:</p>

<ul>
    <li>Construct a <code>Thread</code> object using the <code>Runnable</code> object, and call 
    <code>start</code> on the <code>Thread</code> object.</li>
    <li>Define a subclass of a <code>Thread</code> object, and override the definition of its 
    <code>run</code> method. Then construct an instance of this subclass and call <code>start</code>
    on that instance directly.</li>
</ul>

</recommendation>
<example>

<p>In the following example, the main thread, <code>ThreadDemo</code>, calls the child thread, 
<code>NewThread</code>, using <code>run</code>. This causes the child thread to run to
completion before the rest of the main thread is executed, so that "Child thread activity" is 
printed before "Main thread activity".</p>

<sample src="CallsToRunnableRun.java" />

<p>To enable the two threads to run concurrently, create the child thread and call 
<code>start</code>, as shown below. This causes the main thread to
continue while the child thread is waiting, so that "Main thread activity" is printed before 
"Child thread activity".</p>

<sample src="CallsToRunnableRunFixed.java" />

</example>
<references>


<li>
  The Java Tutorials: <a href="https://docs.oracle.com/javase/tutorial/essential/concurrency/runthread.html">Defining and Starting a Thread</a>.
</li>
<li>
  SEI CERT Oracle Coding Standard for Java: <a href="https://wiki.sei.cmu.edu/confluence/display/java/THI00-J.+Do+not+invoke+Thread.run()">THI00-J. Do not invoke Thread.run()</a>.
</li>
<li>
  Java API Specification: <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Thread.html">Thread</a>.
</li>
<li>
  Java API Specification: <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Runnable.html">Runnable</a>.
</li>


</references>
</qhelp>