[Pharo-dev] Lock-free Atomic Counter ?
siguctua at gmail.com
Wed Apr 2 19:28:21 EDT 2014
On 3 April 2014 00:11, Sven Van Caekenberghe <sven at stfx.eu> wrote:
> Is it possible to have a simple lock-free atomic counter in Pharo 3.0 ?
> ^ idCounter := idCounter + 1
> Or is it still possible that two process entering this code can mess
> things up ?
> #+ is a message send. So technically, if you will be interrupted at the
returning a result from it, then somebody else could run #nextId without
as result you will get 2 processes returning same value from #nextId.
(and increasing numbers of concurrent processes will produce even more
surprising results :)
> I vaguely remember a discussion about that long ago...
> assignment is atomic.. the one which i use in atomic queue impl., but it
is hidden, undocumented VM implementation detail :) e.g.:
oldA := a.
a := newA.
actually can be any series of it, as long as nothing else there (no message
z := c.
w := e.
will be performed atomically.
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