On Tue, Jun 9, 2015 at 1:43 PM, Mark S. Miller <[email protected]> wrote:
> On Tue, Jun 9, 2015 at 10:38 AM, C. Scott Ananian <[email protected]> > wrote: > >> I think that Promise pipelining works just fine -- you just have to >> implement it inside Promise#get, Promise#put, etc. >> ``` >> // This is already in prfun >> Promise.get = function(fieldname) { return this.then(function(o) { return >> o[fieldname]; }); }; >> // This comes with your RPC mechanism >> class RemoteObjectPromise extends Promise { >> this(args...) { >> let res, rej; >> > if (typeof(args[0]) !== 'string') throw new TypeError("Not a remote >> reference!"); >> > super((a,b)=>{res=a;rej=b;}); >> this.handle = gensym(); >> // first argument to rpcCall is "destination" of the operation >> rpcCall(this.handle, ...args).then( v => res(v), e => rej(v) ); >> }, >> > get(fieldname) { >> > // note that this.handle is a name for the remote object, it is not a >> resolved value. >> // as such, this method doesn't have to wait until the remote object >> corresponding to >> // this.handle is resolved >> return new RemoteObjectPromise('GET', this.handle, fieldname); >> > } >> > } >> ``` >> > What about the interaction between q and r in .then, that I mentioned in > my previous email? That's the reason I changed my mind and now think we > need an extension mechanism besides subclassing in order to make pipelining > work. Note: it needs to work even if p is a plain promise. It is only q > that knows that the scenario is special. > Oh, right, I forgot: ``` RemoteObjectPromise[Symbol.species] = Promise; ``` That takes care of `then()`... And provides another nice use case for species. What would you expect `RemoteObjectPromise.all()` to do in this case? Probably `RemoteObjectPromise.prototype.all()` makes more sense -- if you have a remote reference to a (promised) array, you can pipeline the wait for all the elements in the array, without having to do all the waits on the client side. But in this case `RemoteObjectPromise.prototype.all()` is probably special-cased (and ignores species): ``` RemoteObjectPromise.prototype.all = function() { return new RemoteObjectPromise('ALL', this.handle); }; // And this is what I claim that `Promise.all` should also be: RemoteObjectPromise.all = function(x) { return this.resolve(x).all(); }; ``` Note that, given the definition above (I've tweaked it slightly), `RemoteObjectPromise.resolve(x)` throws TypeError if `x` is not already a remote object reference. You could tweak it to perform a migration or some such if you preferred. --scott
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