poolr

limit parallel execution and serialze when limit is reached

npm install poolr
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poolr.js

Small but usefull resource pooling/limiting/throttling library for node.js.

Poolr runs asyncronous tasks in parallel until a configured limit is reached and then switches to serial execution. This helps maximizing the use of limited resources like filedescriptors or remote (database-) connections.

poolr tries to be small and intuitive to use. For a much more advanced implementation of resource pools take a look at node-pool. If you only want to pool http request, take a look at node's builtin http.Agent.maxSockets.

You can add any function you like to a pool:

staticFunc(foo, bar, callback) becomes: thisPool.addTask(staticFunc, foo, bar, callback);

For object methods you can either pass the object as a default context as a second argument to the constructor of poolr, or use function binding:

var someObj = new someClass();
var thisPool = poolr.createPool(10, someObj);
thisPool.addTask(someObj.someMethod, arg1, argN, callback);

or:

var someObj = new someClass();
var thisPool = poolr.createPool(10);
thisPool.addTask(someObj.someMethod.bind(someObj), arg1, argN, callback);

If you only need one pool, you can just create it during require:

var myPool = require('poolr').createPool(10);

Synopsis

A basic example limiting cradle connections to two at a time:

var cradle = require('cradle'),
    poolr  = require('poolr').createPool;

cradle.setup({host: 'localhost', port: 5984});
var conn      = new (cradle.Connection)(),
    db        = conn.database('test'),
    couchPool = poolr(2, db);

// all cradle functions are called via the pool:
couchPool.addTask(db.exists, function(err, result) {
    if (err) throw err;
        console.log(result + ' exists');
    }
});
couchPool.addTask(db.save, {foo:'bar'}, function(err, res) {
    if (err) throw err;
    console.log(res);
});
// ...and so on.
// Add more as fast as you like. Only two functions will be run at a time

createPool

createPool() ceates a new reource pool. The constructor takes one integer argument representing the maximum number of tasks allowed for using this resource in parallel. If you want to support a default context for binding functions to, you can supply it as a second argument.

poolr.createPool(5); creates a resource pool for 5 parallel exections poolr.createPool(5, someObj); creates a resource pool for 5 parallel executions with someObj as this context for tasks.

addTask()

add a task to the resource pool. Takes the function to be called as the first argument. Later arguments are passed to the function. The last argument is expected to be a callback to pass back the results. If the function is an object method and needs its object context, you should either supply the object as a second argument to the poolr constructor or bind the method to its object:

var obj = new someClass();
myPool = poolr.createPool(10, obj);

addTask(staticFunction, arg1, argn, callback);

addTask(otherObj.someFunction.bind(otherObj), arg1, argn, callback);

myPool.addTask(obj.someFunction, arg1, argn, callback);

addTask() returns true if the task is run immediately and false if it will be run within the next free slot.

Events

throttle

poolr will emit throttle when the limit is reached and tasks are being queued.

drain

poolr will emit drain as soon as there are free slots in the task queue again.

last

poolr will emit last after the last task in the queue has been started.

idle

poolr will emit idle after the last task in the queue has finished.

Node.js is an official trademark of Joyent. This module is not formally related to or endorsed by the official Joyent Node.js open source or commercial project.

License

(The MIT License)

Copyright (c) 2011 Bernhard Weisshuhn bkw@codingforce.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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