@worker-tools/deno-kv-storage
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An implementation of the StorageArea (1,2,3) interface for Deno with an extensible system for supporting various database backends.
58 lines • 2.64 kB
JavaScript
// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
/**
* pooledMap transforms values from an (async) iterable into another async
* iterable. The transforms are done concurrently, with a max concurrency
* defined by the poolLimit.
*
* If an error is thrown from `iterableFn`, no new transformations will begin.
* All currently executing transformations are allowed to finish and still
* yielded on success. After that, the rejections among them are gathered and
* thrown by the iterator in an `AggregateError`.
*
* @param poolLimit The maximum count of items being processed concurrently.
* @param array The input array for mapping.
* @param iteratorFn The function to call for every item of the array.
*/
export function pooledMap(poolLimit, array, iteratorFn) {
// Create the async iterable that is returned from this function.
const res = new TransformStream({
async transform(p, controller) {
controller.enqueue(await p);
},
});
// Start processing items from the iterator
(async () => {
const writer = res.writable.getWriter();
const executing = [];
try {
for await (const item of array) {
const p = Promise.resolve().then(() => iteratorFn(item));
// Only write on success. If we `writer.write()` a rejected promise,
// that will end the iteration. We don't want that yet. Instead let it
// fail the race, taking us to the catch block where all currently
// executing jobs are allowed to finish and all rejections among them
// can be reported together.
p.then((v) => writer.write(Promise.resolve(v))).catch(() => { });
const e = p.then(() => executing.splice(executing.indexOf(e), 1));
executing.push(e);
if (executing.length >= poolLimit) {
await Promise.race(executing);
}
}
// Wait until all ongoing events have processed, then close the writer.
await Promise.all(executing);
writer.close();
}
catch {
const errors = [];
for (const result of await Promise.allSettled(executing)) {
if (result.status == "rejected") {
errors.push(result.reason);
}
}
writer.write(Promise.reject(new AggregateError(errors, "Threw while mapping."))).catch(() => { });
}
})();
return res.readable[Symbol.asyncIterator]();
}
//# sourceMappingURL=pool.js.map