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parallel-ware

0.0.1 • Public • Published

parallel-ware

Execute middleware in parallel. For executing in series, see ware.

Example

The following example runs all the middleware in parallel.

var parallel = require('parallel-ware');
 
function add (val) {
  return function (calc, next) {
    calc.sum += val;
    console.log(calc.sum);
    next();
  };
}
 
// executes in parallel, no order guarenteed
var middleware = parallel()
  .use(add(1))
  .use(add(2))
  .use(add(3));
 
middleware.run({ sum: 0 }, function (err, result) {
  // all the middleware has run, calc.sum equals 6
});
 
// 2
// 5
// 6

Wait to Execute

You can also tell parallel-ware to wait to execute a middleware until a specific condition is met. The .when(wait, fn) method takes the wait function as an optional first parameter.

var parallel = require('parallel-ware');
 
function add (val) {
  return function (calc, next) {
    calc.sum += val;
    console.log(calc.sum);
    next();
  };
}
 
function equals (val) {
  return function (calc, next) {
    next(null, calc.sum === val);
  };
}
 
var middleware = parallel()
  .use(add(1))
  .when(equals(4), add(2)) // executes after sum === 4
  .when(equals(10), add(10)) // executes after sum === 10, which never happens
  .use(add(3));
 
middleware.run({ sum: 0 }, function (err, calc) {
  // all the middleware has run, calc.sum equals 6
});
 
// 3
// 4
// 6

Managing Concurrency

You can limit the concurrency with which the middleware will get executed.

var middleware = parallel()
  .concurrency(2)
  .use(constantContact())
  .use(linkedin())
  .use(facebook())
  .use(github());

Monitoring Progress

And you can listen for progress events (following the same structure as visionmedia/batch progress events).

var middleware = parallel()
  .use(constantContact())
  .use(linkedin())
  .use(facebook())
  .use(github());
 
middleware.on('progress', function (progress) {
  
});
 
middleware.run({ email: 'michael.bolton@initech.com' });

Error Handling

Middleware errors don't stop the overall execution, but are rather passed back in batch.

var parallel = require('parallel-ware');
 
function add (val) {
  return function (calc, next) {
    calc.sum += val;
    next();
  };
}
 
function fail (animal) {
  return function (calc, next) {
    next(new Error(animal));
  };
}
 
// executes in parallel, no order guarenteed
var middleware = parallel()
  .use(add(1))
  .use(fail('porcupine'))
  .use(add(2))
  .use(fail('whale'))
  .use(add(3));
 
middleware.run({ sum: 0 }, function (err, calc) {
  if (err) {
    console.log(err);
    console.log(err.errors)
  }
  console.log(calc.sum);
});
 
// Error: 2 error(s) encountered.
// [Error: Whale, Error: Porcupine]
// 6

API

parallel()

Create a parallel middleware execution pipeline.

.use(fn)

Add a middleware fn to the execution pipeline.

.when(wait, fn)

Add a middleware fn to the execution pipeline to run after the wait says it can.

The wait function supports a synchronous signature:

function equals (val) {
  return function (calc) {
    return calc.sum === val;
  };
}
 
var middleware = parallel()
  .use(add(1))
  .when(equals(4), add(2)) // executes after sum === 4
  .when(equals(10), add(10)) // executes after sum === 10, which never happens
  .use(add(3));
 
middleware.run({ sum: 0 }, function (err, calc) {
  // all the middleware has run, calc.sum equals 6
});

And an asynchronous signature:

function equals (val) {
  return function (calc, next) {
    next(null, calc.sum === val);
  };
}
 
var middleware = parallel()
  .use(add(1))
  .when(equals(4), add(2)) // executes after sum === 4
  .when(equals(10), add(10)) // executes after sum === 10, which never happens
  .use(add(3));
 
middleware.run({ sum: 0 }, function (err, calc) {
  // all the middleware has run, calc.sum equals 6
});

.concurrency(max)

Limit the amount of concurrently executing middleware to max.

.on('progress', ..

Listen on progress events.

License

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     /  |           \
    /o o|    MIT     \
    \___/||_||__||_|| *
         || ||  || ||
        _||_|| _||_||
       (__|__|(__|__|

Copyright (c) 2013 Segment.io <friends@segment.io>

Versions

Current Tags

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    Downloads (Last 7 Days)
    • Tag
  • 0.0.1
    156
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Version History

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    Downloads (Last 7 Days)
    • Published
  • 0.0.1
    156

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Install

npm i parallel-ware

Repository

github.com/segmentio/parallel-ware

Homepage

github.com/segmentio/parallel-ware#readme

Weekly Downloads

3

Version

0.0.1

License

MIT

Last publish

Collaborators

  • ivolo
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