Stop running processes after a Promise is rejected

Question 1

Stop running processes after a Promise is rejected

javascript node.js promise bluebird

user4209821 · Feb 8, 2016 · Viewed 8.3k times · Source

Answer

Answer

As @Esailija pointed out bluebird has cancellation mechanism built-in - which is really nice and for sure totally fine for simple async computations.

Promise.config({
  cancellation: true
});

function createCancellableMock(result, time) {

  return new Promise(function(resolve, reject, onCancel) {

    // var child = runCommand();
    var token = setTimeout(function() {
      if (result) {
        console.log('almost done', result);
        resolve(result);
      } else {
        reject('_ERR_');
      }
    }, time);

    onCancel(function() {
      console.log('cancelling');
      // child.kill('SIGTERM');
      clearTimeout(token);
    })
  })

}

var op1 = createCancellableMock('ok-1', 1000);
//var op2 = createCancellableMock('ok-2', 500);
var op2 = createCancellableMock(null, 500); // will be rejected

Promise.all([op1, op2])
  .spread(function(v1, v2) {
    console.log('BOTH-OK', v1, v2)
  })
  .catch(function() {
    console.error('ERROR');
    op1.cancel();
  })
  .finally(function() {
    console.log('finally');
  })

<script src="https://cdnjs.cloudflare.com/ajax/libs/bluebird/3.3.0/bluebird.core.js"></script>

UPDATE

You can cancel recursively defined actions (such as retries). The best strategy in such a case is not to mangle the action itself with the recursive behavior. In the below snippet I created a very simple wrapper which illustrates my point.

var TOO_MANY_RETRIES_ERROR = 'too_many_retries_error';
var PROB_OF_FAIL = 0.8;
var INTERVAL = 200;
var RETRIES = 5;

var CANCEL_AFTER = null;
//var CANCEL_AFTER = INTERVAL * (RETRIES/2);

Promise.config({
  cancellation: true
});

function retryWithCancel(params) {

  // params = {op - operation to retry (it should return a promise, which either ),
  // interval - between retries, retries - number of retries }

  console.log('running, retries left ', params.retries);

  params = Object.assign({}, params); // copy params - no side-effects please
  params.retries--;
  if (params.retries <= 0) {
    console.error('too many retries');
    return Promise.reject(new Error(TOO_MANY_RETRIES_ERROR));
  }

  return new Promise(function(resolve, reject, onCancel) {

    var o = params.op()
      .catch(function() {
        return Promise.delay(params.interval)
          .then(retryWithCancel.bind(null, params))
          .catch(reject)
      })
      .then(resolve)


    onCancel(function() {
      console.log('Cancelling, retries left: ', params.retries);
      o.cancel();
    });

  })

}

function fakeOperation() {

  return Promise.delay(100)
    .then(function() {
      if (Math.random() > PROB_OF_FAIL) {
        return Promise.resolve('SUCCESS');
      } else {
        return Promise.reject(new Error('ERROR'));
      }

    })
}

var p = retryWithCancel({
    op: fakeOperation,
    interval: INTERVAL,
    retries: RETRIES
  })
  .then(console.log.bind(console))
  .catch(console.error.bind(console))
  .finally(console.log.bind(console, 'done'))

if (CANCEL_AFTER) {
  setTimeout(function() {
    p.cancel();
  }, CANCEL_AFTER)
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/bluebird/3.3.1/bluebird.js"></script>

ORIGINAL ANSWER

In general promises are great but they do not offer cancellation mechanism out of the box. It is pretty problematic in some scenarios (e.g. https://github.com/whatwg/fetch/issues/27) and in your case option to cancel would be pretty handy as well. The only valid option is to add it yourself.

basic promise based solution

I distilled the problem to bare minimum and made it browser runnable. The downside of the below approach is that after cancellation the promise will never resolve nor reject - which in general case is surely unacceptable. Alternatively .cancel may reject the promise with some special symbol. Neither of these approaches seem elegant.

function createCancellableMock(result, time) {
    
    // child = null;
    var token = null ;
    var p = new Promise(function(resolve, reject) {
        
        // child = runCommand();
        token = setTimeout(function() {
            if (result) {
                console.log('almost done', result);
                resolve(result);
            } 
            else {
                reject('_ERR_');
            }
        }, time);
    }
    )
    
    return {
        promise: p,
        cancel: function() {
            console.log('cancelling');
            // child.kill('SIGTERM');
            clearTimeout(token);
        }
    }
}

var op1 = createCancellableMock('ok-1', 1000);
// var op2 = createCancellableMock('ok-2', 500);
var op2 = createCancellableMock(null, 500); // will be rejected

Promise.all([op1.promise, op2.promise])
.then(function(vs) { // no spread in native implemantation
    console.log('BOTH-OK', vs[0], vs[1])
})
.catch(function() {
    console.error('ERROR');
    op1.cancel();
})

observable based solution

For basic sequence of operations promises are fine, but there is a way more superior approach available: namely observables. Not only they offer built-in cancellation / disposing mechanism, but allow to deal with multiple values emitted and keep sophisticated async execution under very strict control.

  function createCancellableMock(result, time) {

    return Rx.Observable.create(function(observer) {

      var done = false;
      var token = setTimeout(function() {
        if (result) {
          console.log('almost done: ' + result);
          observer.onNext(result);
          observer.onCompleted();
        } else {
          observer.onError('_ERR_');
        }
      }, time);

      // this will be called upon `disposed`
      return function() {
        console.log('disposing, done: ', done);
        if (!done) {
          clearTimeout(token);
        }
      }

    })

  }

  var op1 = createCancellableMock('ok-1', 1000);
  //var op2 = createCancellableMock('ok-2', 500);
  var op2 = createCancellableMock(null, 500); // will be rejected

  op1.zip(op2)
    .catch(function(err) {
      // it was disposed automatically :) hurray
      console.log('Caught', err);
      // return Rx.Observable.empty(); // swallowing
      return Rx.Observable.throw(err); // throwing

    })
    .subscribe(function(vs) {
        console.log('BOTH-OK', vs[0], vs[1])
      },
      function(err) {
        console.error('Unhandled error', err);
      },
      function() {
        console.log('Upon successful termination.')
      }
    );

<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/4.0.7/rx.all.js"></script>

Question 2

I'm using the following code which working OK, but the problem is that when I get an error, I want it to stops all the other promises. For example if chi.getCommand(val1, val2), will send a reject and I got to the exception catch, I want to cancel the promises for chss.exe and app.getStatus(12); How can I achieve that?

  var start = Promise.all([
      chi.getCommand(val1, val2),
      chi.findAndUpdateCustomer()
    ]).spread(function (command, customer) {
        return chss.exe(runnableDoc, command, customer)
                 .delay(10)
                 .then(function (val) {
                   if (val) console.log(val);
                   return app.getStatus(12);
                 });
    }).catch(function (err) {
        // catch and handle errors and when it come to here I want it to stops all the chain above
    });

This is the code of get command in short:

function getCommand(method, cmd) {
  return new Promise(function (resolve, reject) {
    ...
    child.stderr.on('data', function (data) {
        console.log('stderr: here!' + data);
        reject(data);
    });
}

The console log stderr: here! are printed so the resolve are called!

UPDATE1

The only thing which stops the getStatus is when I put the process.exit(1) But this kill all the process, I just want to stop all the chain of the function getCommand in case Im arriving to the catch block,

is there a way?

is it bug in blueBird ? I use "bluebird": "2.9.34"

function getCommand(method, cmd) { return new Promise(function (resolve, reject) {

var spawn = require('child_process').spawn;
var ls = spawn("cmdbug",["/c","npm install express --save"]);


    ls.on('error', function (err) {
        console.log(err);
        reject(err);
    });

the error which I got is

{ [Error: spawn cmdr ENOENT] code: 'ENOENT', errno: 'ENOENT', syscall: 'spawn cmdbug', path: 'cmdr', spawnargs: [ '/g', 'npm install express --save' ] } { [Error: spawn cmdbug ENOENT] code: 'ENOENT', errno: 'ENOENT', syscall: 'spawn cmdbug', path: 'cmdr', spawnargs: [ '/g', 'npm install express --save' ] } Child process failed with code -4058

And still the process of getStatus is writing to the console.

The code which I use and not for testing is:

The getCommand is the function that throw the error!

var start= function () {
    return new Promise.all([
        childP.getChildProcessCommand(val1, val2),
        childP.findAndUpdateCustomer()
    ]).spread(function (cmd, updated) {
            //Execute child process
            return Promise.all([
                childP.getCommand('spawn', cmd),
                app.getStatus(51000,10,1);
            ]).catch(function (err) {
                // catch and handle errors
                console.log("An error occur: " + err);
                return;
            })
        }).catch(function (err) {
            // catch and handle errors
            console.log("An error occur: " + err);
            return;
        })
}();

The code for check status is:

// Returns a promise that resolves when the port is open

checkPortStatus: function(port, host){
  return new Promise((resolve, reject) => {
    portscanner.checkPortStatus(port, host, function(error, status) {
      if(error)
        reject(error);
      else if(status === 'open')
        resolve(status);
      else
        reject(new Error('Port is not open'));
    });
  });
},

// THE API function
getStatus: function(port, retriesLeft) {

  const TIME_BETWEEN_CHECKS = 1000;
  const HOST = '127.0.0.1';
  const RETRIES = 20;
  retriesLeft = retriesLeft === void 0 ? RETRIES : retriesLeft;

  if(!port) throw new Error('Port is required');
  if(retriesLeft === 0) Promise.reject('Timed Out');

  return new Promise((resolve, reject) => {

    // If it rejects, we do added work.
    this.checkPortStatus(port, host).then(resolve, error => {
     console.log("Waiting for port " + port + " attempt: " + retry);
      setTimeout(() => {

        this.getStatus(port, retriesLeft - 1).then(resolve, reject);

      }, TIME_BETWEEN_CHECKS);
    });
  });
}

And I see the error in the console and still see the console log of the following for 10 attempts. console.log("Waiting for port " + port + " attempt: " + retry);

UPDATE2 When trying to change As @artur suggest in the second option I got error in the recoursive call the error is:

TypeError: Cannot read property 'then' of undefined

This is what I've tried:

getStatus: function(port, retriesLeft) {

  const TIME_BETWEEN_CHECKS = 1000;
  const HOST = '127.0.0.1';
  const RETRIES = 20;
  retriesLeft = retriesLeft === void 0 ? RETRIES : retriesLeft;

  if(!port) throw new Error('Port is required');
  if(retriesLeft === 0) Promise.reject('Timed Out');

  var promise = new Promise((resolve, reject) => {

    // If it rejects, we do added work.
    this.checkPortStatus(port, host).then(resolve, error => {
     console.log("Waiting for port " + port + " attempt: " + retry);
      setTimeout(() => {
        //The error in the following recursive call
        this.getStatus(port, retriesLeft - 1).then(resolve, reject);

      }, TIME_BETWEEN_CHECKS);
      }).catch(function (error) {
         return reject(error);
     });
        return {
            promise:promise,
    cancel: function() {
        console.log('cancelling');
        clearTimeout(token);
        }

       }
    });
  });
}

Stop running processes after a Promise is rejected

Answer

UPDATE

ORIGINAL ANSWER

basic promise based solution

observable based solution

Related questions