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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><title>Java Image I/O API Guide: 2 - Goals</title></head><body bgcolor="#ffffff"> <table summary="layout" width="100%"><tr><td><!-- Bug in Communicator w/font: NavBar text disappears for Times 14pt pref. --><!-- font size="-1" --> <a href="imageio_guideTOC.fm.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/imageio_guideTOC.fm.html">CONTENTS</a> | <a href="goals.fm1.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/goals.fm1.html">PREV</a> | <a href="apps.fm1.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/apps.fm1.html">NEXT</a> <!-- | <a href="copyright.fm.html">INDEX</a> --><!-- /font --></td><td align=right><i>Java<sup><font size="-1">TM</font></sup></font> Image I/O API Guide</i></td></tr></table><br> <p><hr size="8" width="35%" align="left" noshade><h2><a name="997090"><i>2.2 </i> Non-Goals</a></h2><blockquote><a name="997091"><!-- --></a><i><b> Thread Safety</b></i></blockquote><blockquote><a name="997092"><!-- --></a>A particular instance of an <code>ImageReader</code> or <code>ImageWriter</code> is not required to support re-entrant (simultaneous) calls to its methods (with the exception of the <code>abort</code> method that requests current read or writes to halt). However, it must be possible for multiple instances of the same plug-in class to operate simultaneously. For the sake of brevity, we will only discuss reader plug-ins below.<p><a name="997115"><!-- --></a>Supporting full re-entrancy would require that the reader bundle all of its state information (e.g., the current input source) into a separate state object, which would allow methods in progress to continue to work with the settings that were in effect at the time they began, while allowing a separate thread to modify the state to be used by the next operation.<p><a name="997112"><!-- --></a>Rather than forcing each <code>ImageReader</code> to keep track of its state in this way, it is simpler to require the application to instantiate multiple instances of the same <code>ImageReader</code> class if it wishes to perform multithreaded processing. This means that the state of an <code>ImageReader</code> must be maintained using non-static instance variables only, which should not be a burden for plug-in developers.<p></blockquote><br><hr><!-- Bug in Communicator w/font: NavBar text disappears for Times 14pt pref. --><!-- font size="-1" --> <a href="imageio_guideTOC.fm.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/imageio_guideTOC.fm.html">CONTENTS</a> | <a href="goals.fm1.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/goals.fm1.html">PREV</a> | <a href="apps.fm1.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/apps.fm1.html">NEXT</a> <!-- | <a href="copyright.fm.html">INDEX</a> --><!-- /font --><hr><font size="-1"><i><A HREF="copyright.fm.html" tppabs="http://java.sun.com/j2se/1.4.2/docs/guide/imageio/spec/copyright.fm.html">Copyright</a> © 2001 Sun Microsystems, Inc. All Rights Reserved.</i></font><!-- This HTML file was created with Quadralay WebWorks Publisher 3.5.0 --><!-- by Suzette Pelouch --><!-- Last updated: Fri Apr 27 11:11:16 2001 --> </body><script language="JavaScript" src="s_code_remote.js" tppabs="http://java.sun.com/js/omi/jsc/s_code_remote.js"></script></html>⌨️ 快捷键说明
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