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<h1 id="title">FBB::SharedMutex(3bobcat)</h1>
<h2 id="author">Shared Memory Mutex<br/>(libbobcat-dev_4.08.02-x.tar.gz)</h2>
<h2 id="date">2005-2017</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_4.08.02-x.dsc</em>: detached signature;
<li> <em >bobcat_4.08.02-x.tar.gz</em>: source archive;
<li> <em >bobcat_4.08.02-x_i386.changes</em>: change log;
<li> <em >libbobcat1_4.08.02-x_*.deb</em>: debian package holding the
libraries;
<li> <em >libbobcat1-dev_4.08.02-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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