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59 lines
1.4 KiB
JavaScript
59 lines
1.4 KiB
JavaScript
5 years ago
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/*
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## Purpose
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To avoid running expensive IO or computation concurrently.
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If the result of IO or computation is requested while an identical request
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is already in progress, wait until the first one completes and provide its
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result to every routine that requested it.
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## Usage
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Provide:
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1. a named key for the computation or resource,
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2. a callback to handle the result
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3. an implementation which calls back with the result
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```
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var batch = Batch();
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var read = function (path, cb) {
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batch(path, cb, function (done) {
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console.log("reading %s", path);
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fs.readFile(path, 'utf8', done);
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});
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};
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read('./pewpew.txt', function (err, data) {
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if (err) { return void console.error(err); }
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console.log(data);
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});
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read('./pewpew.txt', function (err, data) {
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if (err) { return void console.error(err); }
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console.log(data);
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});
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```
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*/
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module.exports = function () {
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var map = {};
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return function (id, cb, impl) {
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if (typeof(cb) !== 'function' || typeof(impl) !== 'function') {
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throw new Error("expected callback and implementation");
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}
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if (map[id]) { return void map[id].push(cb); }
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map[id] = [cb];
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impl(function () {
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var args = Array.prototype.slice.call(arguments);
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map[id].forEach(function (h) {
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h.apply(null, args);
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});
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delete map[id];
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});
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};
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};
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