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Man Pages


Manual Reference Pages  -  SHAREDMUTEX (3)

NAME

FBB::SharedMutex - Mutex for shared memory

CONTENTS

SYNOPSIS

#include <bobcat/sharedmutex>
Linking option: -lpthread, -lbobcat

DESCRIPTION

Shared memory may be used by multiple processes. To synchronize access to shared memory an FBB::SharedMutex may be defined inside a shared memory segment. SharedMutex objects allows clients to lock a shared memory segment before reading or writing its contents. E.g., the Bobcat class FBB::SharedSegment defines a SharedMutex in its shared memory segment.

The SharedMutex class uses the facilities offered by the PThread library to implement (non recursive) shared memory locking. To force unlocking a (possibly) locked shared memory segment, its destructor can be called.

SharedMutex mutexes are non-recursive, resulting in deadlocks if their lock member is called twice from the same thread of execution without an intermediate call to unlock the mutex. If this causes concern, a variable can be defined indicating whether the lock has already been obtained.

NAMESPACE

FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the namespace FBB.

INHERITS FROM

-

CONSTRUCTORS, DESTRUCTOR

o SharedMutex():
The default constructor initializes an FBB::SharedMutex object to a shared memory mutex (using the PTHREAD_PROCESS_SHARED attribute). As an FBB::SharedMutex object will normally be defined inside a shared memory segment the object\(cqs 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 d_shared, and an FBB::SharedMutex should be defined at d_shared\(cqs address, then the FBB::SharedMutex object can be initialized like this:

new (d_shared) FBB::SharedMutex;

Caveat: when using placement new to initialize a SharedMutex make sure that the SharedMutex fits inside a block (i.e., shared.blockOffset() + sizeof(SharedMemory) < shared.dataSegmentSize()). If not, use seek to switch to an offset where this equality holds true, or simply use SharedMemory::create like this:

FBB::SharedMemory::create<FBB::SharedMutex>();

o ~SharedMutex():
The class\(cqs destructor releases all of the current process\(cqs nested shared memory segment locks. To destroy an FBB::SharedMutex object that has been constructed using the placement new operator use

d_sharedMutex->~SharedMutex();

(assuming SharedMutex *d_sharedMutex points to the location where placement new has previously initialized the FBB::SharedMutex object.)
Copy and move constructors are not available.

MEMBER FUNCTIONS

o void lock() const:
When returning from this member, the current process has locked the shared memory segment. Note that SharedMutex objects are non-recursive.
o void unlock() const:
The object\(cqs lock of the shared memory segment is released. This member can also be called if the SharedMutex\(cqs lock has not been obtained.

PROTECTED MEMBER FUNCTION

o pthread_mutex_t *mutexPtr():
A pointer is returned to the pthread_mutex_t object used by the SharedMutex object;

EXAMPLE

See the sharedstream(3bobcat) man page.

FILES

bobcat/sharedmutex - defines the class interface

SEE ALSO

bobcat(7) isharedstream(3bobcat), osharedstream(3bobcat), sharedblock(3bobcat), sharedcondition(3bobcat), sharedmemory(3bobcat), (e.g.,) pthread_mutex_init(3posix), sharedpos(3bobcat), sharedreadme(7bobcat), sharedsegment(3bobcat), sharedstream(3bobcat), sharedstreambuf(3bobcat)

BUGS

None Reported.

DISTRIBUTION FILES

o bobcat_3.25.01-x.dsc: detached signature;
o bobcat_3.25.01-x.tar.gz: source archive;
o bobcat_3.25.01-x_i386.changes: change log;
o libbobcat1_3.25.01-x_*.deb: debian package holding the libraries;
o libbobcat1-dev_3.25.01-x_*.deb: debian package holding the libraries, headers and manual pages;
o http://sourceforge.net/projects/bobcat: public archive location;

BOBCAT

Bobcat is an acronym of ‘Brokken\(cqs Own Base Classes And Templates\(cq.

COPYRIGHT

This is free software, distributed under the terms of the GNU General Public License (GPL).

AUTHOR

Frank B. Brokken (f.b.brokken@rug.nl).

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libbobcat-dev_3&.25&.01-x&.tar&.gz FBB::SHAREDMUTEX (3bobcat) 2005-2015

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