Linking option: -lpthread, -lbobcat
DESCRIPTIONShared 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.
All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the namespace FBB.
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:
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.
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
A pointer is returned to the pthread_mutex_t object used by the SharedMutex object;
EXAMPLESee the sharedstream(3bobcat) man page.
FILESbobcat/sharedmutex - defines the class interface
- bobcat_4.02.00-x.dsc: detached signature;
- bobcat_4.02.00-x.tar.gz: source archive;
- bobcat_4.02.00-x_i386.changes: change log;
- libbobcat1_4.02.00-x_*.deb: debian package holding the libraries;
- libbobcat1-dev_4.02.00-x_*.deb: debian package holding the libraries, headers and manual pages;
http://sourceforge.net/projects/bobcat: public archive location;
BOBCATBobcat is an acronym of `Brokken's Own Base Classes And Templates'.
COPYRIGHTThis is free software, distributed under the terms of the GNU General Public License (GPL).
AUTHORFrank B. Brokken ([email protected]).