[whatwg] Application defined "locks"

[Scott Hess]

On Thu, Sep 10, 2009 at 2:38 PM, James Robinson<jamesr at google.com> wrote:
> I also strongly feel that giving web
> developers access to locking mechanisms is a bad idea - it hasn't been a
> spectacular success in any other language.

I think that you can either give web developers a strong set of
concurrent-programming primitives, or you can give them a weak set and
let them make up what they think they need out of those.  The nice
thing about providing a very basic primitives is that it's more likely
that good developers can compose higher-level operations with the
primitives.

A few years back I proposed to some coworkers that it would be
interesting to model JavaScript IPC on an existing well-formed system,
such as Mach.  On the surface, that sounds crazy, but once someone
finds that they need to figure out how to have some code process a
MessagePort in database transaction under a critical section, well,
then it makes more sense to have modeled the primitives on a research
project rather than be added in an ad hoc fashion.

> I think the useful semantics are equivalent to the following (being careful
> to avoid mentioning 'locks' or 'mutexes' explicit):  A script passes in a
> callback and a token.  The UA invokes the callback at some point in the
> future and provides the guarantee that no other callback with that token
> will be invoked in any context within the origin until the invoked callback
> returns.  Here's what I mean with an intentionally horrible name:
> window.runMeExclusively(callback, "arbitrary string token");

Maybe:
  window.runCriticalSection(callback, "identifier");

-scott