ACE_Singleton< TYPE, ACE_LOCK > Class Template Reference

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 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.