Parallel calculations: Difference between revisions

=={{header|JavaScript}}==

This code demonstrates Web Workers. This should work on current versions of Firefox, Safari, Chrome and Opera.

This first portion should be placed in a file called "parallel_worker.js". This file contains the logic used by every worker created.

<lang javascript>

var onmessage = function(event) {

postMessage({"n" : event.data.n,

"factors" : factor(event.data.n),

"id" : event.data.id});

};

function factor(n) {

var factors = [];

for(p = 2; p <= n; p++) {

if((n % p) == 0) {

factors[factors.length] = p;

n /= p;

}

}

return factors;

}

</lang>

This portion appends each of the numbers with their factors as the results arrive into an html tag with the id "result". Once the final worker completes its task (worker_count is reduced to 0), the reduce function is called to determine which number is the answer.

<lang javascript>

var numbers = [12757923, 12878611, 12757923, 15808973, 15780709, 197622519];

var workers = [];

var worker_count = 0;

var results = [];

for(var i = 0; i < numbers.length; i++) {

worker_count++;

workers[i] = new Worker("parallel_worker.js");

workers[i].onmessage = accumulate;

workers[i].postMessage({n: numbers[i], id: i});

}

function accumulate(event) {

n = event.data.n;

factors = event.data.factors;

id = event.data.id;

result = document.getElementById("result");

ne = document.createElement("p");

ne.appendChild(document.createTextNode(n + " : " + factors));

result.appendChild(ne);

results[id] = {n:n, factors:factors};

// Cleanup - kill the worker and countdown until all work is done

workers[id].terminate();

worker_count--;

if(worker_count == 0)

reduce();

}

function reduce() {

answer = 0;

for(i = 1; i < results.length; i++) {

min = results[i].factors[0];

largest_min = results[answer].factors[0];

if(min > largest_min)

answer = i;

}

n = results[answer].n;

factors = results[answer].factors;

result = document.getElementById("result");

ne = document.createElement("p");

ne.appendChild(document.createTextNode("The number with the relatively largest factors is: " + n + " : " + factors));

result.appendChild(ne);

results[id] = {n:n, factors:factors};

}

</lang>