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# ACE_Singleton 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:

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Collaboration diagram for ACE_Singleton:

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List of all members.

## Public Methods
virtual void | cleanup (void *param=0)
| Cleanup method, used by <ace_cleanup_destroyer> to destroy the ACE_Singleton. More...
## Static Public Methods
TYPE * | instance (void)
| Global access point to the Singleton. More...
void | dump (void)
| Dump the state of the object. More...
## Protected Methods
| ACE_Singleton (void)
| Default constructor. More...
## Static Protected Methods
ACE_Singleton< TYPE, ACE_LOCK > *& | instance_i (void)
| Get pointer to the Singleton instance. More...
## Protected Attributes
TYPE | instance_
| Contained instance. More...
## Static Protected Attributes
ACE_Singleton< TYPE, ACE_LOCK > * | singleton_ = 0
| Pointer to the Singleton (ACE_Cleanup) instance. More...

## 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.

## Constructor & Destructor Documentation

template<class TYPE, class ACE_LOCK>
ACE_INLINE ACE_Singleton< TYPE, ACE_LOCK >::ACE_Singleton | ( | void |  | ) | `[protected]`

| Default constructor.

## Member Function Documentation

template<class TYPE, class ACE_LOCK>
void ACE_Singleton< TYPE, ACE_LOCK >::cleanup | ( | void * | param = 0 | ) | `[virtual]`

| Cleanup method, used by <ace_cleanup_destroyer> to destroy the ACE_Singleton. Reimplemented from ACE_Cleanup.

template<class TYPE, class ACE_LOCK>
void ACE_Singleton< TYPE, ACE_LOCK >::dump | ( | void |  | ) | `[static]`

| Dump the state of the object. Reimplemented in ACE_Unmanaged_Singleton.

template<class TYPE, class ACE_LOCK>
TYPE * ACE_Singleton< TYPE, ACE_LOCK >::instance | ( | void |  | ) | `[static]`

| Global access point to the Singleton. Reimplemented in ACE_Unmanaged_Singleton.

template<class TYPE, class ACE_LOCK>
ACE_Singleton< TYPE, ACE_LOCK > *& ACE_Singleton< TYPE, ACE_LOCK >::instance_i | ( | void |  | ) | `[static, protected]`

| Get pointer to the Singleton instance. Reimplemented in ACE_Unmanaged_Singleton.

## Member Data Documentation

template<class TYPE, class ACE_LOCK>
TYPE ACE_Singleton::instance_`[protected]`

| Contained instance.

template<class TYPE, class ACE_LOCK>
ACE_Singleton< TYPE, ACE_LOCK > * ACE_Singleton< TYPE, ACE_LOCK >::singleton_ = 0`[static, protected]`

| Pointer to the Singleton (ACE_Cleanup) instance. Reimplemented in ACE_Unmanaged_Singleton.

The documentation for this class was generated from the following files:

- Singleton.h
- Singleton.cpp
- Singleton.i