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Add assumeoverride feature option for Java directors to improve performance when it can be assumed that all methods are overridden by the Java derived classes

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git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk@13606 626c5289-ae23-0410-ae9c-e8d60b6d4f22
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William S Fulton 2012-08-13 21:41:08 +00:00
commit 009c191430
6 changed files with 108 additions and 7 deletions
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23
Doc/Manual/Java.html
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@ -86,6 +86,7 @@
<li><a href="#Java_directors_overhead">Overhead and code bloat</a>
<li><a href="#Java_directors_example">Simple directors example</a>
<li><a href="#Java_directors_threading">Director threading issues</a>
<li><a href="#Java_directors_performance">Director performance tuning</a>
</ul>
<li><a href="#Java_allprotected">Accessing protected members</a>
<li><a href="#Java_common_customization">Common customization features</a>
@ -3525,6 +3526,27 @@ Macros can be defined on the commandline when compiling your C++ code, or altern
</pre>
</div>
<H3><a name="Java_directors_performance"></a>24.5.6 Director performance tuning</H3>
<p>
When a new instance of a director (or subclass) is created in Java, the C++ side of the director performs a runtime check per director method to determine if that particular method is overridden in Java or if it should invoke the C++ base implementation directly. Although this makes initialization slightly more expensive, it is generally a good overall tradeoff.
</p>
<p>
However, if all director methods are expected to usually be overridden by Java subclasses, then initialization can be made faster by avoiding these checks via the <tt>assumeoverride</tt> attribute. For example:
</p>
<div class="code">
<pre>
%feature("director", assumeoverride=1) Foo;
</pre>
</div>
<p>
The disadvantage is that invocation of director methods from C++ when Java doesn't actually override the method will require an additional call up into Java and back to C++. As such, this option is only useful when overrides are extremely common and instantiation is frequent enough that its performance is critical.
</p>
<H2><a name="Java_allprotected"></a>24.6 Accessing protected members</H2>
@ -7862,4 +7884,3 @@ Many of these have runtime tests in the java subdirectory.
</body>
</html>