A Singleton Adapter uses the Adapter pattern to turn ordinary classes into Singletons optimized with the Double-Checked Locking optimization pattern. More...

#include <Singleton.h>

Inheritance diagram for ACE_Singleton< TYPE, ACE_LOCK >:

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Collaboration diagram for ACE_Singleton< TYPE, ACE_LOCK >:

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List of all members.

Public Member Functions
virtual void	cleanup (void *param=0)
Static Public Member Functions
static TYPE *	instance (void)
	Global access point to the Singleton.
static void	close (void)
	Explicitly delete the Singleton instance.
static void	dump (void)
	Dump the state of the object.
Protected Member Functions
	ACE_Singleton (void)
	Default constructor.
Static Protected Member Functions
static ACE_Singleton< TYPE, ACE_LOCK > *&	instance_i (void)
	Get pointer to the Singleton instance.
Protected Attributes
TYPE	instance_
	Contained instance.
Static Protected Attributes
static ACE_Singleton< TYPE, ACE_LOCK > *	singleton_ = 0
	Pointer to the Singleton (ACE_Cleanup) instance.

Detailed Description

template<class TYPE, class ACE_LOCK>
class ACE_Singleton< TYPE, ACE_LOCK >

A Singleton Adapter uses the Adapter pattern to turn ordinary classes into Singletons optimized with the Double-Checked Locking optimization pattern.

This implementation is a slight variation on the GoF Singleton pattern. In particular, a single <ACE_Singleton<TYPE, ACE_LOCK> > instance is allocated here, not a <TYPE> instance. The reason for this is to allow registration with the ACE_Object_Manager, so that the Singleton can be cleaned up when the process exits. For this scheme to work, a (static) cleanup() function must be provided. ACE_Singleton provides one so that TYPE doesn't need to. If you want to make sure that only the singleton instance of <T> is created, and that users cannot create their own instances of <T>, do the following to class <T>: (a) Make the constructor of <T> private (or protected) (b) Make Singleton a friend of <T> Here is an example:

 * class foo
 * {
 * friend class ACE_Singleton<foo, ACE_Null_Mutex>;
 * private:
 * foo () { cout << "foo constructed" << endl; }
 * ~foo () { cout << "foo destroyed" << endl; }
 * };
 * typedef ACE_Singleton<foo, ACE_Null_Mutex> FOO;
 *

Note:: The best types to use for ACE_LOCK are ACE_Recursive_Thread_Mutex and ACE_Null_Mutex. ACE_Recursive_Thread_Mutex should be used in multi-threaded programs in which it is possible for more than one thread to access the <ACE_Singleton<TYPE, ACE_LOCK>> instance. ACE_Null_Mutex can be used otherwise. The reason that these types of locks are best has to do with their allocation by the ACE_Object_Manager. Single ACE_Recursive_Thread_Mutex and ACE_Null_Mutex instances are used for all ACE_Singleton instantiations. However, other types of locks are allocated per ACE_Singleton instantiation.