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Always run limited functions asynchronously #28

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merged 4 commits into from
May 18, 2020
Merged

Always run limited functions asynchronously #28

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247c24f
fix: always run limit fns asynchronously
copperwall May 15, 2020
9692609
refactor: use async function instead of .then
copperwall May 16, 2020
be61486
docs: add comment explaining the await placement in enqueue
copperwall May 17, 2020
08619f6
Update index.js
sindresorhus May 18, 2020
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18 changes: 13 additions & 5 deletions index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -28,11 +28,19 @@ const pLimit = concurrency => {
};

const enqueue = (fn, resolve, ...args) => {
if (activeCount < concurrency) {
run(fn, resolve, ...args);
} else {
queue.push(run.bind(null, fn, resolve, ...args));
}
queue.push(run.bind(null, fn, resolve, ...args));

(async () => {
// This function needs to wait until the next microtask before comparing
// `activeCount` to `concurrency`, because `activeCount` is updated asynchronously
// when the run function is dequeued and called. The comparison in the if-statement
// needs to happen asynchronously as well to get an up-to-date value for `activeCount`.
await Promise.resolve();
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if (activeCount < concurrency && queue.length > 0) {
queue.shift()();
}
})();
};

const generator = (fn, ...args) => new Promise(resolve => enqueue(fn, resolve, ...args));
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8 changes: 7 additions & 1 deletion test.js
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Expand Up @@ -98,6 +98,10 @@ test('activeCount and pendingCount properties', async t => {
t.is(limit.pendingCount, 0);

const runningPromise1 = limit(() => delay(1000));
t.is(limit.activeCount, 0);
t.is(limit.pendingCount, 1);

await Promise.resolve();
t.is(limit.activeCount, 1);
t.is(limit.pendingCount, 0);

Expand All @@ -108,6 +112,7 @@ test('activeCount and pendingCount properties', async t => {
const immediatePromises = Array.from({length: 5}, () => limit(() => delay(1000)));
const delayedPromises = Array.from({length: 3}, () => limit(() => delay(1000)));

await Promise.resolve();
t.is(limit.activeCount, 5);
t.is(limit.pendingCount, 3);

Expand All @@ -121,12 +126,13 @@ test('activeCount and pendingCount properties', async t => {
t.is(limit.pendingCount, 0);
});

test('clearQueue', t => {
test('clearQueue', async t => {
const limit = pLimit(1);

Array.from({length: 1}, () => limit(() => delay(1000)));
Array.from({length: 3}, () => limit(() => delay(1000)));

await Promise.resolve();
t.is(limit.pendingCount, 3);
limit.clearQueue();
t.is(limit.pendingCount, 0);
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