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<title>FBB::SharedMutex</title>
<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
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<h1>FBB::SharedMutex</h1>
<h2>libbobcat-dev_3.23.01-x.tar.gz</h2>
<h2>2005-2014</h2>
<html><head>
<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
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<h1></h1>
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<title>FBB::SharedMutex(3bobcat)</title>
<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
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<body text="#27408B" bgcolor="#FFFAF0">
<hr>
<h1>FBB::SharedMutex(3bobcat)</h1>
<h2>libbobcat-dev_3.23.01-x.tar.gz Shared Memory Mutex</h2>
<h2>2005-2014</h2>
<p>
<h2>NAME</h2>FBB::SharedMutex - Mutex for shared memory
<p>
<h2>SYNOPSIS</h2>
<strong>#include <bobcat/sharedmutex></strong><br>
Linking option: <em>-lpthread, -lbobcat </em>
<p>
<h2>DESCRIPTION</h2>
Shared memory may be used by multiple processes. To synchronize access to
shared memory an <strong>FBB::SharedMutex</strong> may be defined inside a shared memory
segment. <strong>SharedMutex</strong> objects allows clients to lock a shared memory
segment before reading or writing its contents. E.g., the Bobcat class
<em>FBB::SharedSegment</em> defines a <strong>SharedMutex</strong> in its shared memory segment.
<p>
The <strong>SharedMutex</strong> class uses the facilities offered by the
<em>PThread</em> library to implement (non recursive) shared memory locking. To
force unlocking a (possibly) locked shared memory segment, its destructor can
be called.
<p>
<strong>SharedMutex</strong> mutexes are non-recursive, resulting in deadlocks if their
<em>lock</em> member is called twice from the same thread of execution without an
intermediate call to <em>unlock</em> the mutex. If this causes concern, a variable
can be defined indicating whether the lock has already been obtained.
<p>
<h2>NAMESPACE</h2>
<strong>FBB</strong><br>
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace <strong>FBB</strong>.
<p>
<h2>INHERITS FROM</h2>
-
<p>
<h2>CONSTRUCTORS, DESTRUCTOR </h2>
<ul>
<li> <strong>SharedMutex()</strong>:<br>
The default constructor initializes an <strong>FBB::SharedMutex</strong> object to a
shared memory mutex (using the <em>PTHREAD_PROCESS_SHARED</em>
attribute). As an <strong>FBB::SharedMutex</strong> object will normally be defined
inside a shared memory segment the object's memory is already
available. In this case placement new should be used to call the
constructor. E.g., if a shared memory segment is attached to the
current process at <em>d_shared</em>, and an <strong>FBB::SharedMutex</strong> should be
defined at <em>d_shared</em>'s address, then the <strong>FBB::SharedMutex</strong>
object can be initialized like this:
<pre>
new (d_shared) FBB::SharedMutex;
</pre>
Caveat: when using placement new to initialize a <strong>SharedMutex</strong> make
sure that the <strong>SharedMutex</strong> fits inside a block (i.e.,
<em>shared.blockOffset() + sizeof(SharedMemory) <
shared.dataSegmentSize()</em>). If not, use <em>seek</em> to switch to an
offset where this equality holds true, or simply use
<em>SharedMemory::create</em> like this:
<pre>
FBB::SharedMemory::create<FBB::SharedMutex>();
</pre>
<p>
<li> <strong>~SharedMutex()</strong>:<br>
The class's destructor releases all of the current process's nested
shared memory segment locks. To destroy an <strong>FBB::SharedMutex</strong> object
that has been constructed using the placement <em>new</em> operator use
<pre>
d_sharedMutex->~SharedMutex();
</pre>
(assuming <em>SharedMutex *d_sharedMutex</em> points to the location where
placement new has previously initialized the <strong>FBB::SharedMutex</strong>
object.)
<p>
</ul>
Copy and move constructors are not available.
<p>
<h2>MEMBER FUNCTIONS</h2>
<ul>
<li> <strong>void lock() const</strong>:<br>
When returning from this member, the current process has locked the
shared memory segment. Note that <strong>SharedMutex</strong> objects are
non-recursive.
<p>
<li> <strong>void unlock() const</strong>:<br>
The object's lock of the shared memory segment is released. This member
can also be called if the <strong>SharedMutex's</strong> lock has not been
obtained.
</ul>
<p>
<h2>PROTECTED MEMBER FUNCTION</h2>
<ul>
<li> <strong>pthread_mutex_t *mutexPtr()</strong>:<br>
A pointer is returned to the <em>pthread_mutex_t</em> object used by
the <strong>SharedMutex</strong> object;
</ul>
<p>
<h2>EXAMPLE</h2>
See the <strong>sharedstream</strong>(3bobcat) man page.
<p>
<h2>FILES</h2>
<em>bobcat/sharedmutex</em> - defines the class interface
<p>
<h2>SEE ALSO</h2>
<strong>bobcat</strong>(7)
<strong>isharedstream</strong>(3bobcat),
<strong>osharedstream</strong>(3bobcat),
<strong>sharedblock</strong>(3bobcat),
<strong>sharedcondition</strong>(3bobcat),
<strong>sharedmemory</strong>(3bobcat),
(e.g.,) <strong>pthread_mutex_init</strong>(3posix),
<strong>sharedpos</strong>(3bobcat),
<strong>sharedreadme</strong>(7bobcat),
<strong>sharedsegment</strong>(3bobcat),
<strong>sharedstream</strong>(3bobcat),
<strong>sharedstreambuf</strong>(3bobcat)
<p>
<h2>BUGS</h2>
None Reported.
<p>
<h2>DISTRIBUTION FILES</h2>
<ul>
<li> <em>bobcat_3.23.01-x.dsc</em>: detached signature;
<li> <em>bobcat_3.23.01-x.tar.gz</em>: source archive;
<li> <em>bobcat_3.23.01-x_i386.changes</em>: change log;
<li> <em>libbobcat1_3.23.01-x_*.deb</em>: debian package holding the
libraries;
<li> <em>libbobcat1-dev_3.23.01-x_*.deb</em>: debian package holding the
libraries, headers and manual pages;
<li> <em>http://sourceforge.net/projects/bobcat</em>: public archive location;
</ul>
<p>
<h2>BOBCAT</h2>
Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.
<p>
<h2>COPYRIGHT</h2>
This is free software, distributed under the terms of the
GNU General Public License (GPL).
<p>
<h2>AUTHOR</h2>
Frank B. Brokken (<strong>f.b.brokken@rug.nl</strong>).
<p>
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