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