EXECUTION POOL

Node is single threaded but when working with promises it is common to have multiple waiting in parallel. This execution pool allows to queue tasks that return promisses. Setting a limit to the amount of executions that can be actively waiting in paralel.

Current execution strategy works like a queue (FIFO).

If you push a task into the execution pool it will automatically execute if the limit has not been reached yet. Otherwhise it will execute once there is a free slot in the pool.

I needed this for a personal project, so to optimize for time it was done while flying from LHR -> SFO. Meanwhile I have been adding smaller updates. But the concept behind this is to be simplistic and easy to use.

Bellow are some examples:

var ExecutionPool = require("execution-pool"),
    executionPool = new ExecutionPool( POOL_SIZE ),

    task1 = aNewFunctionWhichResolvesAPromiseIn( 10000, spy1 ),
    task2 = aNewFunctionWhichResolvesAPromiseIn( 0, spy2 );
            
executionPool.push( task1 );
executionPool.push( task2 );
...

For clarity the execution-pool expects a function callback that returns a promise (i.e.):

executionPool.push( function() {
    var promise = new Promise();
    
    // ... 
    
    return promise;
});

If you want to be notified when the execution pool gets empty then you can call the utility method getFinishedExecutionPromise. As the name states it returns a promise that will resolve if the pool gets empty.

executionPool.getFinishedExecutionPromise().then( function() {
    console.log("finished executing all promises");
});

Or if you just want to check if your execution pool is still executing you can call isEmpty which returns either true or false;

executionPool.isEmpty(); 

TODO

• Add more execution strategies.
• Improve removal from queue complexity (currently O(N) can be done in O(1))
• Add package.json
• Register in npm https://www.npmjs.org/package/execution-pool
• Add finishin strategies (should the .done be executed internally after the last then?)
• Optimize tests (they are taking more than a second due to the setTimeouts)
• Add timeout options.
• Add a way to detect if the execution pool became empty.
• Remove Q as a internal dependence. (currently there as a quick solution)