feat(cron) implement Deno.cron() (#21019)

This PR adds unstable `Deno.cron` API to trigger execution of cron jobs.

* State: All cron state is in memory. Cron jobs are scheduled according
to the cron schedule expression and the current time. No state is
persisted to disk.
* Time zone: Cron expressions specify time in UTC.
* Overlapping executions: not permitted. If the next scheduled execution
time occurs while the same cron job is still executing, the scheduled
execution is skipped.
* Retries: failed jobs are automatically retried until they succeed or
until retry threshold is reached. Retry policy can be optionally
specified using `options.backoffSchedule`.

1 files changed, 58 insertions, 0 deletions

diff --git a/ext/cron/01_cron.ts b/ext/cron/01_cron.ts
new file mode 100644
index 000000000..a615ae34b
--- /dev/null
+++ b/ext/cron/01_cron.ts
@@ -0,0 +1,58 @@
+// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
+
+// @ts-ignore internal api
+const core = Deno.core;
+
+function cron(
+  name: string,
+  schedule: string,
+  handler: () => Promise<void> | void,
+  options?: { backoffSchedule?: number[]; signal?: AbortSignal },
+) {
+  if (name === undefined) {
+    throw new TypeError("Deno.cron requires a unique name");
+  }
+  if (schedule === undefined) {
+    throw new TypeError("Deno.cron requires a valid schedule");
+  }
+  if (handler === undefined) {
+    throw new TypeError("Deno.cron requires a handler");
+  }
+
+  const rid = core.ops.op_cron_create(
+    name,
+    schedule,
+    options?.backoffSchedule,
+  );
+
+  if (options?.signal) {
+    const signal = options?.signal;
+    signal.addEventListener(
+      "abort",
+      () => {
+        core.close(rid);
+      },
+      { once: true },
+    );
+  }
+
+  return (async () => {
+    let success = true;
+    while (true) {
+      const r = await core.opAsync("op_cron_next", rid, success);
+      if (r === false) {
+        break;
+      }
+      try {
+        const result = handler();
+        const _res = result instanceof Promise ? (await result) : result;
+        success = true;
+      } catch (error) {
+        console.error(`Exception in cron handler ${name}`, error);
+        success = false;
+      }
+    }
+  })();
+}
+
+export { cron };