typedef void (*SilcTaskCallback)(SilcSchedule schedule,
                                     void *app_context,
                                     SilcTaskEvent type, SilcUInt32 fd,
                                     void *context);

    The task callback function.  This function will be called by the
    scheduler when some event of the task is performed.  For example,
    when data is available from the connection this will be called.

    The `schedule' is the scheduler context, the `type' is the indicated
    event, the `fd' is the file descriptor of the task and the `context'
    is a caller specified context. If multiple events occurred this
    callback is called separately for all events.  The `app_context'
    is application specific context that was given as argument to the
    silc_schedule_init function.

    To specify task callback function in the application using the
    SILC_TASK_CALLBACK and SILC_TASK_CALLBACK_GLOBAL macros is
    recommended.