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digitalmars.D.learn - synchonized? correct use? Thread-safe Singleton

reply BLS <nanali nospam-wanadoo.fr> writes:
Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K 
allready explains it to me, but I 've lost the info. :(
Bjoern

class Singleton(T)
{
   public:
   static T instance()
   sychronized       // according to the language spec this should work
   {
     if(_instance is null) _instance = new T;
     return _instance;
   }

   private:
   this() {}

   static T _instance;
}

class Application : Singleton!(Application)
{
}
Jan 04 2008
next sibling parent reply BCS <ao pathlink.com> writes:
Reply to bls,


 Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K
 allready explains it to me, but I 've lost the info. :(
 Bjoern
 class Singleton(T)
 {
 public:
 static T instance()
 sychronized       // according to the language spec this should
 work
 {
 if(_instance is null) _instance = new T;
 return _instance;
 }
 private:
 this() {}
 static T _instance;
 }
 class Application : Singleton!(Application)
 {
 }



I think this will fail because Singleton!(Application).instance() will call 
Application's this() and that is private.

IMHO, a better approach (that I haven't tested) would be to use a mixin:

template Singleton(T)
{
  public:
  static T instance() sychronized
       // according to the language spec this should work
  {
    if(_instance is null) _instance = new T;
    return _instance;
  }
  private:
  this() {}
  static T _instance;
}

class Application : Singleton!(Application)
{
  mixin(Singleton!(typeof(this)));
}
Jan 04 2008
parent reply BLS <nanali nospam-wanadoo.fr> writes:
BCS schrieb:

 Reply to bls,
 

 Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K
 allready explains it to me, but I 've lost the info. :(
 Bjoern
 class Singleton(T)
 {
 public:
 static T instance()
 sychronized       // according to the language spec this should
 work
 {
 if(_instance is null) _instance = new T;
 return _instance;
 }
 private:
 this() {}
 static T _instance;
 }
 class Application : Singleton!(Application)
 {
 }



 I think this will fail because Singleton!(Application).instance() will 
 call Application's this() and that is private.
 
 IMHO, a better approach (that I haven't tested) would be to use a mixin:
 
 template Singleton(T)
 {
  public:
  static T instance() sychronized
       // according to the language spec this should work
  {
    if(_instance is null) _instance = new T;
    return _instance;
  }
  private:
  this() {}
  static T _instance;
 }
 
 class Application : Singleton!(Application)
 {
  mixin(Singleton!(typeof(this)));
 }
 
 



Thanks BCS,

Confused  ...'cause virus infected (me) not the pc


class Application : Singleton!(Application)
{
   mixin(Singleton!(typeof(this)));
   this()
   {
     return instance(this)
   }
}

Honk, that stinks somehow !

Hope I ask not for too much, but please explain the use of the mixin
Bjoern
Jan 04 2008
parent reply BCS <ao pathlink.com> writes:
Reply to bls,


 BCS schrieb:
 

 Reply to bls,
 

 Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K
 allready explains it to me, but I 've lost the info. :(
 Bjoern
 class Singleton(T)
 {
 public:
 static T instance()
 sychronized       // according to the language spec this should
 work
 {
 if(_instance is null) _instance = new T;
 return _instance;
 }
 private:
 this() {}
 static T _instance;
 }
 class Application : Singleton!(Application)
 {
 }



 will call Application's this() and that is private.
 
 IMHO, a better approach (that I haven't tested) would be to use a
 mixin:
 
 template Singleton(T)
 {
 public:
 static T instance() sychronized
 // according to the language spec this should work
 {
 if(_instance is null) _instance = new T;
 return _instance;
 }
 private:
 this() {}
 static T _instance;
 }
 class Application : Singleton!(Application)
 {
 mixin(Singleton!(typeof(this)));
 }



 
 Confused  ...'cause virus infected (me) not the pc
 
 class Application : Singleton!(Application)
 {
 mixin(Singleton!(typeof(this)));
 this()
 {
 return instance(this)
 }
 }
 Honk, that stinks somehow !
 



Oops, typo!!

class Application // no ": ..."


 Hope I ask not for too much, but please explain the use of the mixin



Think of a mixin as a copy/paste + macro. Instance the template (that's the 
macro part) and just lump it into whatever scope you use it in (the copy/paste 
part). It's a quick way to do boiler plate coding.


 Bjoern
Jan 04 2008
parent reply BLS <nanali nospam-wanadoo.fr> writes:
BCS schrieb:

 Reply to bls,
 

 BCS schrieb:


 Reply to bls,


 Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K
 allready explains it to me, but I 've lost the info. :(
 Bjoern
 class Singleton(T)
 {
 public:
 static T instance()
 sychronized       // according to the language spec this should
 work
 {
 if(_instance is null) _instance = new T;
 return _instance;
 }
 private:
 this() {}
 static T _instance;
 }
 class Application : Singleton!(Application)
 {
 }



 will call Application's this() and that is private.

 IMHO, a better approach (that I haven't tested) would be to use a
 mixin:

 template Singleton(T)
 {
 public:
 static T instance() sychronized
 // according to the language spec this should work
 {
 if(_instance is null) _instance = new T;
 return _instance;
 }
 private:
 this() {}
 static T _instance;
 }
 class Application : Singleton!(Application)
 {
 mixin(Singleton!(typeof(this)));
 }




 Confused  ...'cause virus infected (me) not the pc

 class Application : Singleton!(Application)
 {
 mixin(Singleton!(typeof(this)));
 this()
 {
 return instance(this)
 }
 }
 Honk, that stinks somehow !



 Oops, typo!!
 
 class Application // no ": ..."
 

 Hope I ask not for too much, but please explain the use of the mixin



 Think of a mixin as a copy/paste + macro. Instance the template (that's 
 the macro part) and just lump it into whatever scope you use it in (the 
 copy/paste part). It's a quick way to do boiler plate coding.
 

 Bjoern



 




 class Application // no ": ..."















Ah, that makes more sense :)

Okay .
Now; to make it smart .

class Application
{
   class Singleton
   {
   }
}
You mean ... shi. ?

very very big grin
Seriously? I need a bullet proof thread safe singleton implementation ..

Hell I should change my BLS into LS , people here are sometimes confused.
Bjoern
Jan 04 2008
parent reply BCS <ao pathlink.com> writes:
Reply to bls,

 BCS schrieb:

 template Singleton(T)
 {
 public:
 static T instance() sychronized
 // according to the language spec this should work
 {
 if(_instance is null) _instance = new T;
 return _instance;
 }
 private:
 this() {}
 static T _instance;
 }
 class Application : Singleton!(Application)
 {
 mixin(Singleton!(typeof(this)));
 }













 
 class Application // no ": ..."
 
 Ah, that makes more sense :)
 
 Okay .
 Now; to make it smart .
 class Application
 {
 class Singleton
 {
 }
 }
 You mean ... shi. ?
 



Almost. It might not be important, but because Singleton is a template rather 
than a templated class, the inner class you show doesn't exist.

You more or less end up getting this:

 class Application
 {
  public:
  static Application instance() sychronized
  // according to the language spec this should work
  {
   if(_instance is null) _instance = new Application;
   return _instance;
  }
  private:
  this() {}
  static Application _instance;
 }
Jan 04 2008
parent reply BLS <nanali nospam-wanadoo.fr> writes:
BCS schrieb:

 Reply to bls,

 BCS schrieb:

 template Singleton(T)
 {
 public:
 static T instance() sychronized
 // according to the language spec this should work
 {
 if(_instance is null) _instance = new T;
 return _instance;
 }
 private:
 this() {}
 static T _instance;
 }
 class Application : Singleton!(Application)
 {
 mixin(Singleton!(typeof(this)));
 }













 class Application // no ": ..."

 Ah, that makes more sense :)

 Okay .
 Now; to make it smart .
 class Application
 {
 class Singleton
 {
 }
 }
 You mean ... shi. ?



 Almost. It might not be important, but because Singleton is a template 
 rather than a templated class, the inner class you show doesn't exist.
 
 You more or less end up getting this:
 
 class Application
 {
  public:
  static Application instance() sychronized
  // according to the language spec this should work
  {
   if(_instance is null) _instance = new Application;
   return _instance;
  }
  private:
  this() {}
  static Application _instance;
 }
 
 



Last question,(promised) As far as I can remember Sean and I talked 
about to use volatile ...
here it is
http://www.digitalmars.com/d/archives/digitalmars/D/Threadsafe_singleton_using_volatile_synchonized_53768.html

What do you think ?
Bjoern
Jan 04 2008
parent reply BCS <ao pathlink.com> writes:
Reply to bls,


 Okay, I see.
 
 Last question,(promised) As far as I can remember Sean and I talked
 
 about to use volatile ...
 
 here it is
 
 http://www.digitalmars.com/d/archives/digitalmars/D/Threadsafe_singlet
 on_using_volatile_synchonized_53768.html
 
 What do you think ?
 Bjoern



Thread safety isn't my thing, sorry.
Jan 04 2008
parent BLS <nanali nospam-wanadoo.fr> writes:
BCS schrieb:

 Reply to bls,
 

 Okay, I see.

 Last question,(promised) As far as I can remember Sean and I talked

 about to use volatile ...

 here it is

 http://www.digitalmars.com/d/archives/digitalmars/D/Threadsafe_singlet
 on_using_volatile_synchonized_53768.html

 What do you think ?
 Bjoern



 Thread safety isn't my thing, sorry.
Jan 04 2008
prev sibling parent BLS <nanali nospam-wanadoo.fr> writes:
BLS schrieb:

 Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K 
 allready explains it to me, but I 've lost the info. :(
 Bjoern
 
 class Singleton(T)
 {
   public:
   static T instance()
   sychronized       // according to the language spec this should work
   {
     if(_instance is null) _instance = new T;
     return _instance;
   }
 
   private:
   this() {}
 
   static T _instance;
 }
 
 class Application : Singleton!(Application)
 {
 }



Okay, I'll have to think more about this stuff.
In case that somebody can offer a templated (thread-safe and 
bulletproof) Singleton class. ... THANKS
Bjoern
Jan 04 2008