FBB::SharedMutex(3bobcat)
Shared Memory Mutex
(libbobcat-dev_4.08.03-x.tar.gz)
2005-2018
NAME
FBB::SharedMutex - Mutex for shared memory
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
- 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'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 d_shared, and an FBB::SharedMutex should be
defined at d_shared's 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>();
- ~SharedMutex():
The class's destructor releases all of the current process's 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
- void lock() const:
When returning from this member, the current process has locked the
shared memory segment. Note that SharedMutex objects are
non-recursive.
- void unlock() const:
The object's lock of the shared memory segment is released. This member
can also be called if the SharedMutex's lock has not been
obtained.
PROTECTED MEMBER FUNCTION
- 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
- bobcat_4.08.03-x.dsc: detached signature;
- bobcat_4.08.03-x.tar.gz: source archive;
- bobcat_4.08.03-x_i386.changes: change log;
- libbobcat1_4.08.03-x_*.deb: debian package holding the
libraries;
- libbobcat1-dev_4.08.03-x_*.deb: debian package holding the
libraries, headers and manual pages;
- http://sourceforge.net/projects/bobcat: public archive location;
BOBCAT
Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.
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).