updateTask

fn updateTask(io: Io) WorkerError!void {
    // Store this data in the thread so that it does not need to be part of the
    // linker data of the main executable.
    var serialized_buffer: Serialized.Buffer = undefined;
    serialized_buffer.init();
    defer serialized_buffer.batch.cancel(io);

    // In this function we bypass the wrapper code inside `Io.lockStderr` /
    // `Io.tryLockStderr` in order to avoid clearing the terminal twice.
    // We still want to go through the `Io` instance however in case it uses a
    // task-switching mutex.

    try maybeUpdateSize(io, try wait(io, global_progress.initial_delay_ns));
    errdefer {
        const cancel_protection = io.swapCancelProtection(.blocked);
        defer _ = io.swapCancelProtection(cancel_protection);
        const stderr = io.vtable.lockStderr(io.userdata, null) catch |err| switch (err) {
            error.Canceled => unreachable, // blocked
        };
        defer io.unlockStderr();
        clearWrittenWithEscapeCodes(stderr.file_writer) catch {};
    }
    while (true) {
        const buffer, _ = try computeRedraw(io, &serialized_buffer);
        if (try io.vtable.tryLockStderr(io.userdata, null)) |locked_stderr| {
            defer io.unlockStderr();
            global_progress.need_clear = true;
            locked_stderr.file_writer.interface.writeAll(buffer) catch |err| switch (err) {
                error.WriteFailed => return locked_stderr.file_writer.err.?,
            };
        }

        try maybeUpdateSize(io, try wait(io, global_progress.refresh_rate_ns));
    }
}