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<html><!-- #BeginTemplate "/Templates/tmpl.dwt" --><!-- DW6 --><head><!-- #BeginEditable "doctitle" --> <title>PTypes: unit</title><!-- #EndEditable --> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link rel="stylesheet" href="styles.css"></head><body bgcolor="#FFFFFF" leftmargin="40" marginwidth="40"><p><a href="../index.html"><img src="title-20.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.0" border="0"></a> <hr size="1" noshade><!-- #BeginEditable "body" --> <p class="hpath"><a href="index.html">Top</a>: <a href="basic.html">Basic types</a>: unit</p><p> <blockquote> <pre class="lang">#include <pstreams.h>class unit { compref<instm> uin; compref<outstm> uout; virtual void main() = 0; virtual void cleanup() = 0; void connect(unit* next); void run(bool async = false); void waitfor();}</pre></blockquote><p><span class="lang">Units</span> represent functionality similar to console applications in UNIX. Each unit has its own <span class="lang">main()</span> along with input and output 'plugs' - <span class="lang">uin</span> and <span class="lang">uout</span>, that may be mapped to the standard input and output, a local pipe or any other stream compatible with <span class="lang">instm</span> and <span class="lang">outstm</span>, respectively. </p><p>Each unit class must at least override the abstract method <span class="lang">main()</span>. Overridden unit classes typically read input data from <span class="lang">uin</span> and send the result of processing to <span class="lang">uout</span>, like if they were console applications. By default <span class="lang">uin</span> and <span class="lang">uout</span> are attached to standard input and output. After instantiating a unit object you (the user of a unit class) may attach any <span class="lang">instm</span>-compatible stream to <span class="lang">uin</span> and any <span class="lang">outstm</span>-compatible stream to <span class="lang">uout</span>. In addition, units are able to connect to each other using local pipes, and thus form data processing chains within your application.</p><p>You may define other public methods or fields in your unit class that represent additional options. E.g. a regular expression parser unit may have a string field that represents the regular expression itself (see example below).</p><p>Units can be run either synchronously or asynchronously. In the latter case, a separate thread is being created for executing unit's <span class="lang">main()</span> function. If connected to a pipe using <span class="lang">connect()</span>, the first unit in the chain runs within the scope of the calling thread, the others run in separate threads.</p><p>The <span class="lang">unit</span> class is a subclass of <a href="unknown.html">component</a>, and thus it inherits reference counting and delete notification mechanisms from <span class="lang">component</span>. <span class="lang">Unit</span> is declared in <a href="include/pstreams.h.html"><pstreams.h></a>.</p><p>This interface is available only in the multithreaded versions of the library. </p><p><span class="def">compref<instm> unit::uin</span> is a reference-counted pointer to an input stream, that is unit's input 'plug'. By default <span class="lang">uin</span> refers to the standard input object <span class="lang">pin</span>. Typically both <span class="lang">uin</span> and <span class="lang">uout</span> are assigned by the user of the unit after instantiating a unit object. You may assign dynamically allocated stream objects to <span class="lang">uin</span> and <span class="lang">uout</span> - they will be freed automatically by the 'smart' <span class="lang">compref</span> pointer.</p><p><span class="def">compref<outstm> unit::uout</span> -- same as <span class="lang">uin</span>; represents the output 'plug' of the unit.</p><p><span class="def">virtual void unit::main()</span> is unit's main code. Override this method to implement functionality of your mini-process. Note that code in <span class="lang">main()</span> must avoid accessing static/global data, since it may be executed in a separate thread. You may choose to write a reusable unit, i.e. when <span class="lang">main()</span> can be called multiple times for the same object, however <span class="lang">main()</span> is protected from overlapping (recursive) calls, which means, you need not to write reentrant code in this function.</p><p><span class="def">virtual void unit::cleanup()</span> -- override this method to perform finalization and cleanup of a unit. This function is guaranteed to be called even if <span class="lang">main()</span> threw an exception of type <span class="lang">(exception*)</span> or a derivative.</p><p><span class="def">void unit::connect(unit* next)</span> connects a unit object to another object using a local pipe. Multiple units can be connected to form a chain. A user then calls <span class="lang">run()</span> for the first object; all other members of the chain are being started automatically in separate threads.</p><p><span class="def">void unit::run(bool async = false)</span> runs a unit object. This function calls <span class="lang">main()</span> for the given object and possibly for other units, if this is the first object of a chain. You can not call <span class="lang">run()</span> for an object which is not the first in a chain. If <span class="lang">async</span> is <span class="lang">true</span>, this function starts a unit in a separate thread and returns immediately. Use <span class="lang">waitfor()</span> to synchronize with the completion of a unit if started asynchronously.</p><p><span class="def">void unit::waitfor()</span> waits for the unit to terminate if run asynchronously. For unit chains, this method needs to be called only for the first object in a chain.</p><p><b>Example</b>. Consider there is a unit type <span class="lang">ugrep</span> that performs regular expression matching and a unit type <span class="lang">utextconv</span> for converting various text formats. The code below demonstrates how to connect these units and run the chain.</p><blockquote> <pre>#include <pstreams.h>#include "ugrep.h" <span class="comment">// imaginary headers with unit declarations</span>#include "utextconv.h"USING_PTYPESint main(){ ugrep grep; grep.regex = "^abc"; grep.casesens = false; utextconv textconv; textconv.from = CONV_UNIX; textconv.to = CONV_WIN; <span class="comment">// connect the two units and set up the input and output plugs.</span> grep.uin = new ipstream("somehost.com", 8282); grep.connect(&textconv); textconv.uout = new outfile("output.txt"); <span class="comment">// now run the chain; will read input from the socket, pass // through the grep and textconv units and write it to the // output file.</span> grep.run();}</pre></blockquote><p class="seealso">See also: <a href="unknown.html">unknown & component</a>, <a href="streams.html">Streams</a> </p><!-- #EndEditable --><hr size="1"><a href="../index.html" class="ns">PTypes home</a></body><!-- #EndTemplate --></html>⌨️ 快捷键说明
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