Source: ../../../tse3/src/tse3/Mutex.h
|
|
|
|
/*
* @(#)Mutex.h 3.00 2 October 2000
*
* Copyright (c) 2000 Pete Goodliffe (pete@cthree.org)
*
* This file is part of TSE3 - the Trax Sequencer Engine version 3.00.
*
* This library is modifiable/redistributable under the terms of the GNU
* General Public License.
*
* You should have received a copy of the GNU General Public License along
* with this program; see the file COPYING. If not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
*/
#ifndef TSE3_MUTEX_H
#define TSE3_MUTEX_H
namespace TSE3
{
namespace Impl
{
/**
* This class provides an abtract interface for a mutex implementation.
*
* The @ref NullMutexImpl class inherits from this base class, and
* provides a 'null' implementation: performing no lock or unlock
* operations.
*
* This class provides a way of specifying mutex behaviour in a
* platform independant manner.
*
* If you want to use TSE3 in a thread-safe manner then you will
* need to implement a MutexImpl class and pass it to the @ref Mutex
* class.
*
* A MutexImpl is created in an unlocked state.
*
* @short Mutex implementation base class
* @author Pete Goodliffe
* @version 3.00
* @see Mutex
*/
class MutexImpl
{
public:
virtual ~MutexImpl() {}
/**
* Locks the mutex.
*
* If the mutex implementation is already locked by a different
* thread, then this thread will block until the previous one
* unlocks the mutex.
*
* A single thread can lock the mutex multiple times. However,
* subsequent calls to lock have no effect. There must be the
* same number of calls to @ref unlock before the MutexImpl
* is unlocked, though.
*
* @see unlock
*/
virtual void lock() = 0;
/**
* Unlocks the mutex. To unlock the mutex fully, as many
* unlocks must be called as locks.
*
* If the MutexImpl is already unlocked, then nothing
* will happen.
*
* @see lock
*/
virtual void unlock() = 0;
/**
* Returns true if the MutexImpl is locked, false otherwise.
*
* @see lock
* @see unlock
*/
virtual bool locked() = 0;
};
/**
* A default, 'null' implementation of the @ref MutexImpl class that
* is used by thread-unsafe versions of the TSE3 library.
*
* The @ref lock and @ref unlock methods are essentially no-ops - they
* don't perform any locking whatsoever.
*
* @short 'Null' @ref MutexImpl class
* @author Pete Goodliffe
* @version 3.00
* @see MutexImpl
*/
class NullMutexImpl : public MutexImpl
{
public:
NullMutexImpl() : _locked(0) {}
virtual ~NullMutexImpl() {}
/**
* @reimplemented
*/
virtual void lock() { ++_locked; }
/**
* @reimplemented
*/
virtual void unlock() { if (_locked) --_locked; }
/**
* @reimplemented
*/
virtual bool locked() { return _locked; }
private:
int _locked;
};
/**
* The Mutex class is used by TSE3 to ensure thread safety. All
* potentially contenious TSE3 methods claim a Mutex to prevent TSE3
* being entered by multiple threads.
*
* This Mutex class provides a platform independant interface
* to the underlying mutex implementation (which is accessed through
* the @ref MutexImpl class interface).
*
* There is a single, global TSE3 Mutex object that is used by the
* entire library. This is accessed by calling the @ref mutex
* static member function.
*
* On each different platform supported by TSE3 there will be a
* specific @ref MutexImpl class.
*
* By default, the TSE3 library is not configured to be thread safe:
* the default @ref MutexImpl that will be used is the
* @ref NullMutexImpl. This implementation performs no operations
* for lock and unlock.
*
* In order to make TSE3 thread safe, you must have an implementation
* of the @ref MutexImpl class, and pass this to the static
* @ref setImpl method BEFORE using any of the other TSE3 API.
* (In fact, you only need set this before the first call to the
* static @ref mutex method, but most API functions will call this
* at some time).
*
* A simplification of the Mutex API is provided by the
* @ref CritSec class. In some cases this is a more
* convenient interface to use.
*
* @short Mutex class used to ensure TSE3 thread safety
* @author Pete Goodliffe
* @version 3.00
* @see MutexImpl
* @see NullMutexImpl
* @see CritSec
*/
class Mutex
{
public:
/**
* Creates a Mutex object with the specified implementation.
*
* This @ref MutexImpl object is considered to be owned by
* the Mutex class, and will be deleted when the Mutex is
* deleted - you need not delete it yourself.
*
* This does imply that there must be a one-to-one relationship
* between Mutex objects and @ref MutexImpl objects.
*
* A Mutex is created in an unlocked state.
*
* @param impl @ref MutexImpl object to use
*/
Mutex(MutexImpl *i) : impl(i) {}
~Mutex();
/**
* Sets the @ref MutexImpl class that will be used by the
* global Mutex object.
*
* It is very important to call this method BEFORE
* calling @ref mutex to use the global Mutex object. Since
* most TSE3 API methods call mutex, it is safest to set
* the @ref MutexImpl before calling any other TSE3 method.
*
* The impl you specify must exist for as long as you use
* the TSE3 library.
*
* If you do not specify a @ref MutexImpl then a default
* @ref NullMutexImpl will be used, and TSE3 will not
* be thread-safe.
*
* You may only call this once: subsequent calls are ignored
* and the first @ref MutexImpl specified is used.
*
* @param impl @ref MutexImpl to use. This will be deleted
* by the Mutex class - you may forget about it.
*/
static void setImpl(MutexImpl *impl);
/**
* Provides access to the global Mutex object used to lock
* the TSE3 library.
*
* The first time this method is called, a Mutex object will
* be created with the @ref MutexImpl specified by
* @ref setImpl.
*/
static Mutex *mutex();
/**
* Locks the Mutex.
*
* If the Mutex is already locked by a different
* thread, then this thread will block until the previous one
* unlocks the mutex.
*
* A single thread can lock the mutex multiple times. However,
* subsequent calls to lock have no effect. There must be the
* same number of calls to @ref unlock before the Mutex
* is unlocked, though.
*
* @see unlock
*/
void lock()
{
#ifndef TSE3_WITHOUT_MUTEX
impl->lock();
#endif
}
/**
* Unlocks the Mutex. To unlock the mutex fully, as many
* unlocks must be called as locks.
*
* If the Mutex is already unlocked, then nothing will happen.
*
* @see lock
*/
void unlock()
{
#ifndef TSE3_WITHOUT_MUTEX
impl->unlock();
#endif
}
private:
MutexImpl *impl;
static MutexImpl *globalImpl;
};
/**
* A 'critical section' class that provides a somewhat more convenient
* interface to the @ref Mutex class. A CritSec object simply locks
* the global @ref Mutex upon creation and unlocks it on destruction.
*
* Therefore, this means that rather than write:
*
* {
* TSE3::Impl::Mutex::mutex()->lock();
* // do something
* TSE3::Impl::Mutex::mutex()->unlock();
* }
*
*
* You can simply write:
*
* {
* TSE3::Impl::CritSec cs;
* // do something
* }
*
*
* Clearly, this prevents a possible source of error, where you might
* forget to unlock the mutex after having locked it. It is also in
* most cases a lot more convenient to use.
*
* The CritSec class is small, simple and implemented with inline
* functions so the resultant generated code for both of the above
* examples is identical.
*
* @short Convenient API for @ref Mutex class
* @author Pete Goodliffe
* @version 3.00
* @see Mutex
*/
class CritSec
{
public:
CritSec()
{
#ifndef TSE3_WITHOUT_MUTEX
Mutex::mutex()->lock();
#endif
}
~CritSec()
{
#ifndef TSE3_WITHOUT_MUTEX
Mutex::mutex()->unlock();
#endif
}
};
};
}
#endif
| Generated by: pete on philemon on Wed May 25 14:40:07 2005, using kdoc 2.0a54. |
