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, 25 insertions, 0 deletions

diff --git a/cli/tsc/dts/lib.deno.unstable.d.ts b/cli/tsc/dts/lib.deno.unstable.d.ts
index 56188f3b8..c758e620c 100644
--- a/cli/tsc/dts/lib.deno.unstable.d.ts
+++ b/cli/tsc/dts/lib.deno.unstable.d.ts
@@ -1319,6 +1319,31 @@ declare namespace Deno {
 
   /** **UNSTABLE**: New API, yet to be vetted.
    *
+   * Create a cron job that will periodically execute the provided handler
+   * callback based on the specified schedule.
+   *
+   * ```ts
+   * Deno.cron("sample cron", "*\/20 * * * *", () => {
+   *   console.log("cron job executed");
+   * });
+   * ```
+   * `backoffSchedule` option can be used to specify the retry policy for failed
+   * executions. Each element in the array represents the number of milliseconds
+   * to wait before retrying the execution. For example, `[1000, 5000, 10000]`
+   * means that a failed execution will be retried at most 3 times, with 1
+   * second, 5 seconds, and 10 seconds delay between each retry.
+   *
+   * @category Cron
+   */
+  export function cron(
+    name: string,
+    schedule: string,
+    handler: () => Promise<void> | void,
+    options?: { backoffSchedule?: number[]; signal?: AbortSignal },
+  ): Promise<void>;
+
+  /** **UNSTABLE**: New API, yet to be vetted.
+   *
    * A key to be persisted in a {@linkcode Deno.Kv}. A key is a sequence
    * of {@linkcode Deno.KvKeyPart}s.
    *