How will the Promise's onFulfilled handlers be implemented to be postponed until no script code is on the stack? about jurassic HOT 3 CLOSED

I was thinking that promise execution would happen at the ScriptEngine level, i.e. at the end of a Execute, Evaluate or ExecuteFile. That avoids any problems with reentrancy and should be faster too (FunctionInstance.Call/CallLateBound is called a lot).

from jurassic.

Hi,

In my case, I have used a Promise polyfill. It relies on javascript methods "setImmediate" (or "setTimeout" with value of 0). But the function are evaluated in an other sequence. With your sample, instead of having "1 3 2" you would have "1 2 3", and the "then" functions are executed on the next loop iteration.

So to use Promise (and other stuff), I have done my own execution loop. First script execution executes the full script, and "while I have pending functions in the stack, tries to execute it". By "try to execute", I mean that a pending promise not resolved is stacked, but not executable (so kept on stack).
In the same maner, I have "setTimeout" and "cancelTimeout" (no need for setInterval yet).

This way, I expose Promises to do threaded operations (WinForms long initialization with UI libs, file loading...) and then, the promise "resolve" is called from other thread, but the "then" functions are called in main loop.

It is not the best solution, but we can say it works like in browsers.

from jurassic.

Hi @paulbartrum,
thanks for your reply!

Running the scheduled Promise handlers at the ScriptEngine level is also what I first thought. However, when I want to run callbacks on the script later (after Execute has finished), I use the FunctionInstance supplied by the script code and then simply use FunctionInstance.Call(...). But in this case, the promise handlers would still need to be called before this Call returns if this FunctionInstance resolves a promise.

(To clarify, before I run the Script code with ScriptEngine.Execute(...), I set a global API object with .NET methods where the Script can register events by supplying a callback, and the .NET method takes a FunctionInstance as parameter, which I save and then later .Call() to call back the script's handler. Is this the correct way?)

@maitredede Thanks! In our application we also provide e.g. a setInterval method to call back a FunctionInstance in a regular interval, and also to register for some internal events that can occur on any time. We also plan to provide an API that uses a Promise for long-running operations (e.g. reading a file), where we store the PromiseInstance internal and later call its resolve method, which then should call back the onFulfilled handlers. (The Callbacks will be called from a different thread than the one which called ScriptEngine.Execute(), but we ensure through locking that only one thread at a time calls a script function.)

Currently, we also use a Promise polyfill that uses an internal setImmediate function, which stores the FunctionInstances and invokes them as soon as either the ScriptEngine.Execute() (initialization) or the FunctionInstance.Call() (callback) returns.

Thank you!

from jurassic.