Re: Atomic and singleton

Freedom fighter <>
Fri, 24 Aug 2007 22:33:57 +0100
Gianni Mariani wrote:

Freedom fighter wrote:


Is a singleton class the same as an atomic class? I know that a
singleton class
can only be instantiated once, but does that concept apply to an
atomic class?

Atomic usually refers to multi-threaded applications. Atomic would mean
that any operation performed on the class would happen in such a way as
the only "visible" states were the state prior to an operation and the
state after the operation was complete. Intermediate states would not
be visible to any other threads.

A classic is an "atomic" int. e.g.

int val = 0;

int f()
   return ++ val; // not atomic ...
atomic_int val = 0;

int f()
   return ++ val; // is atomic

In the first example, "++ val" needs to read, increment and write, not
to mention issues with cache ceherency. In the second example the magic
"atomic_int" class performs it's operations using special hardware
instructions so that multiple threads calling f() simultaneously will be

Ah, so that's it then! Thanks so much for that.

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