InconsistentAccess.qhelp

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


<overview>
<p>If a field is mostly accessed in a synchronized context, but occasionally accessed in a non-synchronized way, 
the non-synchronized accesses may lead to race conditions.
</p>

</overview>
<recommendation>

<p>Ensure that the non-synchronized field accesses are made synchronized, if required.</p>

</recommendation>
<example>

<p>In the following example, <code>counter</code> is accessed in a synchronized way in 
<i>all but one</i> cases. If <code>modifyCounter</code> is called by a large number of threads that
are running concurrently, the value of <code>counter</code> at the end of each call may not be zero. 
This is because the non-synchronized statement could be interleaved with updates to the counter that 
are performed by the other threads.</p>

<sample src="InconsistentAccess.java" />

<p>To correct this, the last statement of <code>modifyCounter</code> should be enclosed in a 
<code>synchronized</code> statement.</p>

</example>
<references>


<li>
  Java Language Specification:
  <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-17.html#jls-17.1">Synchronization</a>.
</li>


</references>
</qhelp>