Feature #14706: Atomic Integer incr/decr

• Status: Closed
• Assignee: -
• Target version: -

[mperham (Mike Perham)]

Ruby does not any thread-safe way to implement simple counters without a Mutex. Today Ruby provides Integer#succ but this funcalls "+", making it thread-unsafe as far as I know.

I'd propose adding Integer#incr(amount=1) and Integer#reset which would use atomic operations, giving us thread-safe, high-performance counters.

counter = 0
counter.incr # => 1
counter.incr(10) # => 11
counter.incr(-1) # => 10
counter.reset # => 10
counter # => 0

[mperham (Mike Perham)]

• Tracker changed from Bug to Feature
• Backport deleted (2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN)

[rosenfeld (Rodrigo Rosenfeld Rosas)]

I've always missed that feature as well, so I'm +1 to this. This and many other built-in thread-safe helpers by the way ;)

[jeremyevans0 (Jeremy Evans)]

I think this feature in general is a good candidate for addition to stdlib.

I don't think the Integer class is appropriate for this, because (some) Integers are immediate values, and all Integers are frozen, and you can't modify them. Integer#+ and Integer#succ are thread safe (they return new objects, they do not modify existing objects), it's counter += 1 that is not thread safe.

In terms of naming, maybe Integer::Counter since that is unlikely to conflict with existing code, with an API like:

counter = Integer::Counter.new(0) # maybe default to 0 if no argument?
counter.incr     # => 1
counter.incr(10) # => 11
counter.incr(-1) # => 10
counter.reset    # => 10
counter.to_int   # => 0
counter.to_i     # => 0

[rafaelfranca (Rafael França)]

Related ticket with some discussion already (and partially rejected) https://bugs.ruby-lang.org/issues/12607

[mperham (Mike Perham)]

Jeremy, good point. I would agree that the different semantics are enough to justify a different class. Namespacing it within the Thread class also seems reasonable, e.g. Thread::Counter so it would be available if you require 'thread'.

[shyouhei (Shyouhei Urabe)]

• Is duplicate of Feature #12607: Ruby needs an atomic integer added

[shevegen (Robert A. Heiler)]

I guess this may come up several times in the future. Would
this be a good candidate for discussion in the upcoming
ruby developer meeting? I don't want to suggest it myself
since I was not the one who started the thread (that was
Mike), but it seems to come up every now and then by
different people, so it may be of some relevance.

Rafael França pointed out that it was parially rejected/closed
but I think that did not come via matz primarily since he
did not comment on it; it may be that other ruby developers
pointed out some problems with it before, like Koichi; but
it may still be good to have matz comment on it so that
people can understand what the remaining problems may be,
if there are some.

[dsisnero (Dominic Sisneros)]

should we revisit this now that we have ractor and Feature #17433

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Closed due to duplication.

[dsisnero (Dominic Sisneros)]

Feature #12607 -