timers: introduce setInterval async iterator

Added setInterval async generator to timers\promises. Utilises async generators to provide an iterator compatible with `for await`. Co-Authored-By: Fabian Cook <[email protected]>
nodejs · Jan 31, 2021 · 42a7f52 · 42a7f52
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diff --git a/doc/api/timers.md b/doc/api/timers.md
@@ -363,6 +363,26 @@ added: v15.0.0
   * `signal` {AbortSignal} An optional `AbortSignal` that can be used to
     cancel the scheduled `Immediate`.
 
+### `timersPromises.setInterval([delay[, value[, options]]])`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `delay` {number} The number of milliseconds to wait between iterations.
+   **Default**: `1`.
+* `value` {any} A value with which the iterator returns.
+* `options` {Object}
+  * `ref` {boolean} Set to `false` to indicate that the scheduled `Timeout`
+    between iterations should not require the Node.js event loop to
+    remain active.
+    **Default**: `true`.
+  * `signal` {AbortSignal} An optional `AbortSignal` that can be used to
+    cancel the scheduled `Timeout` between operations.
+  * `throwOnAbort` {boolean} Set to `true` to indicate that the iterator
+    should finish regularly when the signal is aborted. When set to `false`
+    the iterator throws after it yields all values.
+    **Default**: `false`
+
 [Event Loop]: https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/#setimmediate-vs-settimeout
 [`AbortController`]: globals.md#globals_class_abortcontroller
 [`TypeError`]: errors.md#errors_class_typeerror

diff --git a/lib/timers.js b/lib/timers.js
@@ -215,6 +215,16 @@ function setInterval(callback, repeat, arg1, arg2, arg3) {
   return timeout;
 }
 
+
+ObjectDefineProperty(setInterval, customPromisify, {
+  enumerable: true,
+  get() {
+    if (!timersPromises)
+      timersPromises = require('timers/promises');
+    return timersPromises.setInterval;
+  }
+});
+
 function clearInterval(timer) {
   // clearTimeout and clearInterval can be used to clear timers created from
   // both setTimeout and setInterval, as specified by HTML Living Standard:

diff --git a/lib/timers/promises.js b/lib/timers/promises.js
@@ -111,7 +111,86 @@ function setImmediate(value, options = {}) {
       () => signal.removeEventListener('abort', oncancel)) : ret;
 }
 
+async function* setInterval(after, value, options = {}) {
+  if (options == null || typeof options !== 'object') {
+    throw new ERR_INVALID_ARG_TYPE(
+      'options',
+      'Object',
+      options);
+  }
+  const { signal, ref = true, throwOnAbort = true } = options;
+  validateAbortSignal(signal, 'options.signal');
+  if (typeof ref !== 'boolean') {
+    throw new ERR_INVALID_ARG_TYPE(
+      'options.ref',
+      'boolean',
+      ref);
+  }
+
+  if (typeof throwOnAbort !== 'boolean') {
+    throw new ERR_INVALID_ARG_TYPE(
+      'options.throwOnAbort',
+      'boolean',
+      ref);
+  }
+
+  if (signal?.aborted) {
+    if (throwOnAbort) throw new AbortError();
+    return;
+  }
+
+  let onCancel;
+  let notYielded = 0;
+  let passCallback;
+  let abortCallback;
+  const interval = new Timeout(() => {
+    notYielded++;
+    if (passCallback) {
+      passCallback();
+      passCallback = undefined;
+      abortCallback = undefined;
+    }
+  }, after, undefined, true, true);
+  if (!ref) interval.unref();
+  insert(interval, interval._idleTimeout);
+  if (signal) {
+    onCancel = () => {
+      // eslint-disable-next-line no-undef
+      clearInterval(interval);
+      if (abortCallback) {
+        abortCallback(new AbortError());
+        passCallback = undefined;
+        abortCallback = undefined;
+      }
+    };
+    signal.addEventListener('abort', onCancel, { once: true });
+  }
+
+  while (!signal?.aborted) {
+    if (notYielded === 0) {
+      try {
+        await new Promise((resolve, reject) => {
+          passCallback = resolve;
+          abortCallback = reject;
+        });
+      } catch (err) {
+        if (throwOnAbort) {
+          throw err;
+        }
+        return;
+      }
+    }
+    for (; notYielded > 0; notYielded--) {
+      yield value;
+    }
+  }
+  if (throwOnAbort) {
+    throw new AbortError();
+  }
+}
+
 module.exports = {
   setTimeout,
   setImmediate,
+  setInterval,
 };
diff --git a/test/parallel/test-timers-promisified.js b/test/parallel/test-timers-promisified.js
@@ -15,10 +15,12 @@ const timerPromises = require('timers/promises');
 
 const setTimeout = promisify(timers.setTimeout);
 const setImmediate = promisify(timers.setImmediate);
+const setInterval = promisify(timers.setInterval);
 const exec = promisify(child_process.exec);
 
 assert.strictEqual(setTimeout, timerPromises.setTimeout);
 assert.strictEqual(setImmediate, timerPromises.setImmediate);
+assert.strictEqual(setInterval, timerPromises.setInterval);
 
 process.on('multipleResolves', common.mustNotCall());
 
@@ -50,6 +52,66 @@ process.on('multipleResolves', common.mustNotCall());
   }));
 }
 
+{
+  const controller = new AbortController();
+  const { signal } = controller;
+  const iterable = setInterval(1, undefined, { signal });
+  const iterator = iterable[Symbol.asyncIterator]();
+  const promise = iterator.next();
+  promise.then(common.mustCall((result) => {
+    assert.ok(!result.done);
+    assert.strictEqual(result.value, undefined);
+    controller.abort();
+    return assert.rejects(iterator.next(), /AbortError/);
+  }));
+}
+
+{
+  const controller = new AbortController();
+  const { signal } = controller;
+  const iterable = setInterval(1, undefined, { signal, throwOnAbort: false });
+  const iterator = iterable[Symbol.asyncIterator]();
+  const promise = iterator.next();
+  promise.then(common.mustCall((result) => {
+    assert.ok(!result.done);
+    assert.strictEqual(result.value, undefined);
+    controller.abort();
+    return iterator.next();
+  })).then(common.mustCall((result) => {
+    assert.ok(result.done);
+  }));
+}
+
+{
+  const controller = new AbortController();
+  const { signal } = controller;
+  const iterable = setInterval(1, 'foobar', { signal });
+  const iterator = iterable[Symbol.asyncIterator]();
+  const promise = iterator.next();
+  promise.then(common.mustCall((result) => {
+    assert.ok(!result.done);
+    assert.strictEqual(result.value, 'foobar');
+    controller.abort();
+    return assert.rejects(iterator.next(), /AbortError/);
+  }));
+}
+
+{
+  const controller = new AbortController();
+  const { signal } = controller;
+  const iterable = setInterval(1, 'foobar', { signal, throwOnAbort: false });
+  const iterator = iterable[Symbol.asyncIterator]();
+  const promise = iterator.next();
+  promise.then(common.mustCall((result) => {
+    assert.ok(!result.done);
+    assert.strictEqual(result.value, 'foobar');
+    controller.abort();
+    return iterator.next();
+  })).then(common.mustCall((result) => {
+    assert.ok(result.done);
+  }));
+}
+
 {
   const ac = new AbortController();
   const signal = ac.signal;
@@ -78,6 +140,33 @@ process.on('multipleResolves', common.mustNotCall());
   assert.rejects(setImmediate(10, { signal }), /AbortError/);
 }
 
+{
+  const ac = new AbortController();
+  const { signal } = ac;
+  ac.abort(); // Abort in advance
+
+  const iterable = setInterval(1, undefined, { signal });
+  const iterator = iterable[Symbol.asyncIterator]();
+
+  assert.rejects(iterator.next(), /AbortError/);
+}
+
+{
+  const ac = new AbortController();
+  const { signal } = ac;
+
+  const iterable = setInterval(100, undefined, { signal });
+  const iterator = iterable[Symbol.asyncIterator]();
+
+  // This promise should take 100 seconds to resolve, so now aborting it should
+  // mean we abort early
+  const promise = iterator.next();
+
+  ac.abort(); // Abort in after we have a next promise
+
+  assert.rejects(promise, /AbortError/);
+}
+
 {
   // Check that aborting after resolve will not reject.
   const ac = new AbortController();
@@ -95,6 +184,23 @@ process.on('multipleResolves', common.mustNotCall());
   });
 }
 
+{
+  [1, '', Infinity, null, {}].forEach((ref) => {
+    const iterable = setInterval(10, undefined, { ref });
+    assert.rejects(() => iterable[Symbol.asyncIterator]().next(), /ERR_INVALID_ARG_TYPE/);
+  });
+
+  [1, '', Infinity, null, {}].forEach((signal) => {
+    const iterable = setInterval(10, undefined, { signal });
+    assert.rejects(() => iterable[Symbol.asyncIterator]().next(), /ERR_INVALID_ARG_TYPE/);
+  });
+
+  [1, '', Infinity, null, true, false].forEach((options) => {
+    const iterable = setInterval(10, undefined, options);
+    assert.rejects(() => iterable[Symbol.asyncIterator]().next(), /ERR_INVALID_ARG_TYPE/);
+  });
+}
+
 {
   // Check that timer adding signals does not leak handlers
   const signal = new NodeEventTarget();
@@ -165,3 +271,73 @@ process.on('multipleResolves', common.mustNotCall());
     assert.strictEqual(stderr, '');
   }));
 }
+
+{
+  exec(`${process.execPath} -pe "const assert = require('assert');` +
+    'const interval = require(\'timers/promises\')' +
+    '.setInterval(1000, null, { ref: false });' +
+    'interval[Symbol.asyncIterator]().next()' +
+    '.then(assert.fail)"').then(common.mustCall(({ stderr }) => {
+    assert.strictEqual(stderr, '');
+  }));
+}
+
+{
+  async function runInterval(fn, intervalTime, signal) {
+    const input = 'foobar';
+    const interval = setInterval(intervalTime, input, { signal });
+    let iteration = 0;
+    for await (const value of interval) {
+      const time = Date.now();
+      assert.strictEqual(value, input);
+      await fn(time, iteration);
+      iteration++;
+    }
+  }
+
+  {
+    const controller = new AbortController();
+    const { signal } = controller;
+
+    let prevTime;
+    let looped = 0;
+    const delay = 20;
+    const timeoutLoop = runInterval((time) => {
+      looped++;
+      if (looped === 5) controller.abort();
+      if (looped > 5) throw new Error('ran too many times');
+      if (prevTime && time - prevTime < delay) {
+        const diff = time - prevTime;
+        throw new Error(`${diff} between iterations, lower than ${delay}`);
+      }
+      prevTime = time;
+    }, delay, signal);
+
+    assert.rejects(timeoutLoop, /AbortError/);
+    timeoutLoop.catch(common.mustCall(() => {
+      assert.strictEqual(5, looped);
+    }));
+  }
+
+  {
+    // Check that if we abort when we have some callbacks left,
+    // we actually call them.
+    const controller = new AbortController();
+    const { signal } = controller;
+    const delay = 10;
+    let totalIterations = 0;
+    const timeoutLoop = runInterval(async (time, iterationNumber) => {
+      if (iterationNumber === 1) {
+        await setTimeout(delay * 3);
+        controller.abort();
+      }
+      if (iterationNumber > totalIterations) {
+        totalIterations = iterationNumber;
+      }
+    }, delay, signal);
+
+    timeoutLoop.catch(common.mustCall(() => {
+      assert.ok(totalIterations >= 3);
+    }));
+  }
+}