[erlang-questions] Gproc synchronization primitives?

[Ulf Wiger]

Hi Greg,

I've been thinking about adding such a function, so…

Try the new version I just pushed (v0.2.3), and see if it helps.

gproc_dist:sync() is the function to call.

As a general comment, at least gen_leader ensures that replication happens before the reply is delivered to a leader_call(). This is so that the caller should not be surprised by the newly written data not being there when the call returns.

BR,
Ulf W

On 19 Apr 2011, at 23:18, Gregory Haskins wrote:

> Does any mechanism exist to synchronize with the distribution protocol
> in gproc?  Heres what I am running into at the moment:
> 
> I have an FSM which runs out at an arbitrary end-point that registers a
> bunch of {p, g, } properties:
> 
> https://github.com/ghaskins/edist/blob/6f2ab65114c9f92586d3fed17e463eec5742a070/agent/app/src/main/erlang/session_fsm.erl#L23
> 
> Later, that FSM might receive an async event that the "controller"
> service is now available which compels the FSM process to communicate
> with that remote process:
> 
> https://github.com/ghaskins/edist/blob/6f2ab65114c9f92586d3fed17e463eec5742a070/agent/app/src/main/erlang/session_fsm.erl#L30
> 
> The problem with my current design is the controller_api:join() RPC is
> expecting to have visibility to the properties registered in the gproc
> namespace.  Given that the FSM in question and the gproc distribution
> mechanism are independent entities, I have thus introduced a race
> condition (and one that almost always loses, I am finding).
> 
> Here are some possible ways to fix it:
> 
> 1) some kind of gproc:sync() primitive, or even gproc:sync(Node).  Not
> sure if this already exists, could be easily invented if not, or would
> be frowned upon?
> 
> 2) use gproc:await() (and friends) to discover the controller, with the
> premise being that "if I can see you, you can presumably see me".  Not
> sure if this assumption is true?
> 
> 3) Stop trying to use gproc in a timing sensitive way? (FWIW: I used to
> pass the property-list as a parameter in the RPC before I switched over
> the gproc, which of course did not have the race issue).
> 
> Any other suggestions?
> 
> Kind Regards,
> -Greg
> 

Ulf Wiger, CTO, Erlang Solutions, Ltd.
http://erlang-solutions.com