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/* -*- C++ -*- */
// $Id$
// ============================================================================
//
// = LIBRARY
// ace
//
// = FILENAME
// Singleton.h
//
// = DESCRIPTION
//
// = AUTHOR
// Tim Harrison (harrison@cs.wustl.edu), Douglas C. Schmidt, Chris
// Lahey, Rich Christy, and David Levine.
//
// ============================================================================
#ifndef ACE_SINGLETON_H
#define ACE_SINGLETON_H
#include "ace/Synch.h"
#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */
template <class TYPE, class ACE_LOCK>
class ACE_Singleton : public ACE_Cleanup
{
// = TITLE
// A Singleton Adapter uses the Adapter pattern to turn ordinary
// classes into Singletons optimized with the Double-Checked
// Locking optimization pattern.
//
// = DESCRIPTION
// 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.
//
public:
static TYPE *instance (void);
// Global access point to the Singleton.
virtual void cleanup (void *param = 0);
// Cleanup method, used by <ace_cleanup_destroyer> to destroy the
// <ACE_Singleton>.
static void dump (void);
// Dump the state of the object.
protected:
ACE_Singleton (void);
// Default constructor.
TYPE instance_;
// Contained instance.
#if !defined (ACE_LACKS_STATIC_DATA_MEMBER_TEMPLATES)
static ACE_Singleton<TYPE, ACE_LOCK> *singleton_;
// Pointer to the Singleton (ACE_Cleanup) instance.
#endif /* ACE_LACKS_STATIC_DATA_MEMBER_TEMPLATES */
static ACE_Singleton<TYPE, ACE_LOCK> *&instance_i (void);
// Get pointer to the Singleton instance.
};
template <class TYPE, class ACE_LOCK>
class ACE_TSS_Singleton : public ACE_Cleanup
{
// = TITLE
// This class uses the Adapter pattern to turn ordinary classes
// into Thread-specific Singletons optimized with the
// Double-Checked Locking optimization pattern.
//
// = DESCRIPTION
// This implementation is another variation on the GoF Singleton
// pattern. In this case, a single <ACE_TSS_Singleton<TYPE,
// LOCK> > instance is allocated here, not a <TYPE> instance.
// Each call to the <instance> static method returns a Singleton
// whose pointer resides in thread-specific storage. As with
// <ACE_Singleton>, we use 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.
public:
static TYPE *instance (void);
// Global access point to the Singleton.
virtual void cleanup (void *param = 0);
// Cleanup method, used by <ace_cleanup_destroyer> to destroy the
// singleton.
static void dump (void);
// Dump the state of the object.
protected:
ACE_TSS_Singleton (void);
// Default constructor.
ACE_TSS_TYPE (TYPE) instance_;
// Contained instance.
#if !defined (ACE_LACKS_STATIC_DATA_MEMBER_TEMPLATES)
static ACE_TSS_Singleton<TYPE, ACE_LOCK> *singleton_;
// Pointer to the Singleton (ACE_Cleanup) instance.
#endif /* ACE_LACKS_STATIC_DATA_MEMBER_TEMPLATES */
static ACE_TSS_Singleton<TYPE, ACE_LOCK> *&instance_i (void);
// Get pointer to the TSS Singleton instance.
};
#if defined (__ACE_INLINE__)
#include "ace/Singleton.i"
#endif /* __ACE_INLINE__ */
#if defined (ACE_TEMPLATES_REQUIRE_SOURCE)
#include "ace/Singleton.cpp"
#endif /* ACE_TEMPLATES_REQUIRE_SOURCE */
#if defined (ACE_TEMPLATES_REQUIRE_PRAGMA)
#pragma implementation ("Singleton.cpp")
#endif /* ACE_TEMPLATES_REQUIRE_PRAGMA */
#endif /* ACE_SINGLETON_H */
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