batchCancel

fn batchCancel(userdata: ?*anyopaque, batch: *Io.Batch) void {
    const ev: *Evented = @ptrCast(@alignCast(userdata));
    _ = ev;
    batchDrainReady(batch) catch |err| switch (err) {
        error.Timeout => unreachable, // no timeout
    };
    var index = batch.pending.head;
    if (index == .none) return;
    var cancel_region: CancelRegion = .initBlocked();
    defer cancel_region.deinit();
    const thread = cancel_region.awaitIoUring() catch |err| switch (err) {
        error.Canceled => unreachable, // blocked
    };
    while (index != .none) {
        const pending = &batch.storage[index.toIndex()].pending;
        thread.enqueue().* = .{
            .opcode = .ASYNC_CANCEL,
            .flags = linux.IOSQE_CQE_SKIP_SUCCESS,
            .ioprio = 0,
            .fd = 0,
            .off = 0,
            .addr = @intFromPtr(&pending.userdata) | 0b10,
            .len = 0,
            .rw_flags = 0,
            .user_data = @backingInt(Completion.Userdata.wakeup),
            .buf_index = 0,
            .personality = 0,
            .splice_fd_in = 0,
            .addr3 = 0,
            .resv = 0,
        };
        index = pending.node.next;
    }
    while (batch.pending.head != .none) batchDrainReady(batch) catch |err| switch (err) {
        error.Timeout => unreachable, // no timeout
    };
}