batchCancel

fn batchCancel(userdata: ?*anyopaque, batch: *Io.Batch) void {
    const ev: *Evented = @ptrCast(@alignCast(userdata));
    var index = batch.pending.head;
    while (index != .none) {
        const storage = &batch.storage[index.toIndex()];
        const pending = &storage.pending;
        const operation_userdata: *BatchOperationUserdata = .fromErased(&pending.userdata);
        assert(operation_userdata.batch == batch);
        operation_userdata.source.cancel();
    }
    const queue: c.dispatch.queue_t = @ptrCast(batch.userdata orelse return);
    if (batch.pending.head != .none) {
        var waiter: BatchWaiter = .{
            .sleeper = .init(ev.queue, Thread.current().currentFiber()),
            .queue = queue,
            .timer = BatchWaiter.already_signaled,
        };
        if (batch.pending.head == .none) queue.async(&waiter, &BatchWaiter.signal);
        queue.as_object().set_context(&waiter);
        ev.yield(.{ .@"resume" = queue.as_object() });
    }
    batch.userdata = null;
}