Async handling

[espruino-discuss3]

Posted at 2014-12-31 by JumJum

Promises are a powerful tool to avoid callback-hell.
For Espruino I was searching for a tiny solution and found 7 Lines from Krasimir.
Based on this I wrote a simple flow solution.

var async = function(funcs,scope,done ) {
  var _seq = 0,stopped = false;
  this.scope = scope;
  this.next = function(){this.goto(_seq,arguments);};
  this.goto = function(seq,args){
    if(seq < funcs.length){
      if(!stopped){ funcs[seq](args);_seq = seq + 1;} }
    else{done(args);}
  };
  this.exit = function(){stopped = true;done(arguments);};
  this.next();
};

It supports

1. step by step using next()
2. jumping from function to function using goto(funcNr)
3. option to exit in each function using exit()
4. local data using scope-object
5. data handover from function to function, see async2, async3

Handling is simple as you can see here:

function logger(seq,value){ console.log(seq,new Date(),value); }

function async1(){
  async([
      function(){setTimeout(function(){logger("1.0",scope);next();},1000);},
      function(){setTimeout(function(){logger("1.1",scope);next();},1000);}
    ],
    { title:"async1",value: 1},
    function(){logger("1 done",scope);async2();}
  );
}
function async2(){
  async([
      function(){
        scope.n_val = 22;
        setTimeout(function(){logger("2.0",scope);next();},1000);
      },
      function(){setTimeout(function(){logger("2.1",scope);next();},1000);}    
    ],
    { title:"async2",value: 2},
    function(){logger("2 done",scope);async3();}
  );
}
function async3(){
  async([
      function(){setTimeout(function(){logger("3.0",scope);next(33);},1000);},
      function(x){
        scope.n_val = x[0];
        setTimeout(function(){logger("3.1",scope);next();},1000);
      }
    ],
    { title:"async3",value: 3},
    function(){logger("3 done",scope);async4();}
  );
}
function async4(){
  async([
      function(){setTimeout(function(){logger("4.0",scope);goto(2);},1000);},
      function(){setTimeout(function(){logger("4.1",scope);exit();},1000);},
      function(){setTimeout(function(){logger("4.2",scope);goto(1);},1000);},
    ],
    { title:"async4",value: 4},
    function(){logger("4 done",scope);}
  );
}
logger(0,obj);
async1();

[espruino-discuss3]

Posted at 2015-11-28 by tve

Thanks for posting!

Calling next() only seems to work if apply is defined in the global context (not in a module) because this.next = function().... defines the function next at the global level, correct?

And that makes it impossible to nest async's, right?

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Posted at 2015-11-28 by JumJum

I tried to nest asyncs some time ago, and failed :-(
This wasn't important that time, at least for me.
Anyway, now I have the explanation.

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Posted at 2015-11-28 by @allObjects

It's nice to see the job getting done... for the price of 5 globals... not bad.

Reduce the 5 to 1 in the spirit of object-orientation helps with clean-up and passing the one as parm to the sequence defining application functions (async1..4) would conribute to hardening.

I liked the naming in Kazimir's original post: queue... and that it is: queing of sets of asynch operations that have to complete one after the other before a next set is allowed to be entered, and finally chaining these sets.

In some of my implementatins I needed result-dependent follow-up async operation(s) to be completed before the next set could be entered, and therefore allowed an insertion into or append to the funcs array. The effect is similar to a pseudo-multi-level / quasi-context creation (easy to implement by enhancing the next() to accept optionally the required parameters to do it).

Surfing the subject shows many implementations with various focus.

@jumjum, what is the obj's purpose in line 46? Espruino is reporting it undefined...

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Posted at 2015-11-28 by tve

Mhh, I have to read Kazimir's original post...