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111 lines
3.2 KiB
HTML
111 lines
3.2 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<HTML>
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<TITLE>guard - Auto-lock/unlock-er</TITLE>
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<LINK HREF="../pool.css" REL="stylesheet" TYPE="text/css">
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</HEAD>
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<BODY>
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<IMG SRC="../../../../c++boost.gif" WIDTH=276 HEIGHT=86 ALT="C++ Boost">
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<H1 ALIGN=CENTER>guard - Auto-lock/unlock-er</H1>
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<P>
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<H2>Introduction</H2>
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<P>
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detail/guard.hpp provides a type <SPAN CLASS="code">guard<Mutex></SPAN> that allows scoped access to the <SPAN CLASS="code">Mutex</SPAN>'s locking and unlocking operations. It is used to ensure that a <SPAN CLASS="code">Mutex</SPAN> is unlocked, even if an exception is thrown.
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<P>
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<H2>Synopsis</H2>
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<PRE CLASS="code">namespace details {
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namespace pool {
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template <typename Mutex>
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class guard
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{
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private:
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guard(const guard &);
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void operator=(const guard &);
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public:
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explicit guard(Mutex & mtx);
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~guard();
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};
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} // namespace pool
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} // namespace details</PRE>
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<P>
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<H2>Semantics</H2>
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<P>
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<TABLE BORDER ALIGN=CENTER>
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<CAPTION><EM>Symbol Table</EM></CAPTION>
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<TR><TH>Symbol<TH>Meaning
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<TR><TD CLASS="code">T<TD><SPAN CLASS="code">guard<Mutex></SPAN>
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<TR><TD CLASS="code">m<TD>value of type <SPAN CLASS="code">Mutex &</SPAN>
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<TR><TD CLASS="code">g<TD>value of type <SPAN CLASS="code">guard<Mutex></SPAN>
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</TABLE>
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<P>
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<TABLE BORDER ALIGN=CENTER>
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<CAPTION><EM>Requirements on <SPAN CLASS="code">Mutex</SPAN></EM></CAPTION>
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<TR><TH>Expression<TH>Return Type<TH>Assertion/Note/Pre/Post-Condition
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<TR><TD CLASS="code">m.lock()<TD>not used<TD>Locks the mutex referred to by <SPAN CLASS="code">m</SPAN>
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<TR><TD CLASS="code">m.unlock()<TD>not used<TD>Unlocks the mutex referred to by <SPAN CLASS="code">m</SPAN>
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</TABLE>
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<P>
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<TABLE BORDER ALIGN=CENTER>
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<CAPTION><EM>Requirements satisfied by <SPAN CLASS="code">guard</SPAN></EM></CAPTION>
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<TR><TH>Expression<TH>Assertion/Note/Pre/Post-Condition
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<TR><TD CLASS="code">T(m)<TD>Locks the mutex referred to by <SPAN CLASS="code">m</SPAN>; binds <SPAN CLASS="code">T(m)</SPAN> to <SPAN CLASS="code">m</SPAN>
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<TR><TD CLASS="code">(&g)->~T()<TD>Unlocks the mutex that <SPAN CLASS="code">g</SPAN> is bound to
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</TABLE>
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<P>
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<H2>Example</H2>
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<P>
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Given a (platform-specific) <SPAN CLASS="code">mutex</SPAN> class, we can wrap code as follows:
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<PRE CLASS="code">extern mutex global_lock;
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static void f()
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{
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boost::details::pool::guard<mutex> g(global_lock);
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// g's constructor locks "global_lock"
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... // do anything:
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// throw exceptions
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// return
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// or just fall through
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} // g's destructor unlocks "global_lock"</PRE>
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<P>
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<H2>Dependencies</H2>
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<P>
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None.
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<P>
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<H2>Future Directions</H2>
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<P>
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This header will eventually be replaced by a Boost multithreading library.
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<P>
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<HR>
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<P>
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Copyright © 2000, 2001 Stephen Cleary (<A HREF="mailto:shammah@voyager.net">shammah@voyager.net</A>)
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<P>
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This file can be redistributed and/or modified under the terms found in <A HREF="../copyright.html">copyright.html</A>
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<P>
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This software and its documentation is provided "as is" without express or implied warranty, and with no claim as to its suitability for any purpose.
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