<!–Converted with LaTeX2HTML 2022 (Released January 1, 2022) –> <HTML lang="en"> <HEAD> <TITLE>Contents of Mailbox's Layers of Portability</TITLE>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=utf-8"> <META NAME="viewport" CONTENT="width=device-width, initial-scale=1.0"> <META NAME="Generator" CONTENT="LaTeX2HTML v2022">
<LINK REL="STYLESHEET" HREF="MPTSK.css">
<LINK REL="next" HREF="node12_mn.html"> <LINK REL="previous" HREF="node10_mn.html"> <LINK REL="up" HREF="node9_mn.html"> <LINK REL="next" HREF="node12_mn.html"> </HEAD>
<BODY bgcolor="#ffffff" text="#000000" link="#9944EE" vlink="#0000ff" alink="#00ff00">
<H2><A ID="SECTION00042000000000000000"> Mailbox's Layers of Portability</A> </H2>
<P> The Mailbox package is built on three <EM>layers of portability</EM>. Each layer adds a certain degree of functionality and machine independence. The lowest and most device-dependent layer, MPTHD, implements the basic context switching required for any multitasking package; it provides threads of execution. The middle layer, MPTSK, implements scheduling and interprocess communication, non-preemptive multitasking based on MPTHD's; it provides independent, communicating tasks.<A NAME="tex2html7" HREF="footnode_mn.html#foot89" TARGET="footer"><SUP>5</SUP></A> The top layer, MPRES, implements basic resource management for all standard resources and those you may add, preemptive multitasking based on MPTSK's.
<P>
<DIV class="CENTER"><A ID="91"></A> <TABLE> <CAPTION class="BOTTOM"><STRONG>Figure:</STRONG> Mailbox's Portability/Functionality Layers</CAPTION> <TR><TD><IMG STYLE="height: 314.00ex; " SRC="img3.png" ALT="
<P> Since each layer depends only on the layer below it, you may incorporate only the layers necessary to suit your needs. The remainder of this section discusses each of them in detail.
<P>
<HR>
</BODY> </HTML>