68 lines
2.1 KiB
JavaScript
68 lines
2.1 KiB
JavaScript
/*jslint vars: true, plusplus: true, devel: true, nomen: true, indent: 4, maxerr: 50, browser: true */
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/*global postMessage, addEventListener */
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(function () {
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"use strict";
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var WHEN_TO_STOP = 10000000;
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var COMPUTE_BLOCK_SIZE = 1000000;
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var running = false;
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var count = 0;
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// We have to compute in blocks of ~1 second of computation in order to make sure
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// that we read our message queue occasionally. Worker threads are not preemptive
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// (like all JS), so if we don't pause computation to read the message queue, we'll
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// be unresponsive to user requests.
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function compute(start) {
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var n = start;
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var i, hasDivisor;
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if (!running) { // got a message to stop before this call to compute
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postMessage("Stopped!");
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} else {
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while (n < start + COMPUTE_BLOCK_SIZE) {
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hasDivisor = false;
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for (i = 2; i <= Math.sqrt(n); i += 1) {
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if (n % i === 0) {
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hasDivisor = true;
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break;
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}
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}
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if (!hasDivisor) {
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// found a prime!
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count++;
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}
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n += 1;
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}
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if (n < WHEN_TO_STOP) {
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// allow for event loop to actually forward messages to the worker
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setTimeout(function () { compute(n); }, 1);
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} else {
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// we reached the end
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running = false;
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postMessage("Done!");
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}
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}
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// Finally, always report how many primes we've found so far
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postMessage("Found " + count + " primes between 2 and " + (n - 1));
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}
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addEventListener('message', function (event) {
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// doesn't matter what the message is, just toggle the worker
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if (running === false) {
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postMessage("Starting...");
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count = 0;
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running = true;
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compute(1);
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} else {
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postMessage("Stopping...");
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running = false;
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}
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});
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}()); |