Ubuntu Manpage: cron - Tool for automating the period callback of commands

NAME

       cron - Tool for automating the period callback of commands

SYNOPSIS

       package require Tcl  8.6

       package require cron  ?2.1?

       ::cron::at ?processname? timecode command

       ::cron::cancel processname

       ::cron::every processname frequency command

       ::cron::in ?processname? timecode command

       ::cron::object_coroutine object coroutine ?info?

       ::cron::sleep milliseconds

       ::cron::task delete process

       ::cron::task exists process

       ::cron::task info process

       ::cron::task set process field value ?field...? ?value...?

       ::cron::wake ?who?

       ::cron::clock_step milliseconds

       ::cron::clock_delay milliseconds

       ::cron::clock_sleep seconds ?offset?

       ::cron::clock_set newtime

________________________________________________________________________________________________________________

DESCRIPTION

       The cron package provides a Pure-tcl set of tools to allow programs to schedule tasks to occur at regular
       intervals. Rather than force each task to issue it's own call to the event loop, the cron  system  mimics
       the  cron  utility in Unix: on task periodically checks to see if something is to be done, and issues all
       commands for a given time step at once.

       Changes in version 2.0

       While cron was originally designed to handle time scales  >  1  second,  the  latest  version's  internal
       understand  time  granularity  down  to  the  millisecond, making it easier to integrate with other timed
       events.  Version 2.0 also understands how to properly integrate coroutines and objects.  It also  adds  a
       facility for an external (or script driven) clock. Note that vwait style events won't work very well with
       an external clock.

COMMANDS

::cron::at ?processname? timecode command
This command registers a command to be called at the time specified by timecode. If timecode is
expressed as an integer, the timecode is assumed to be in unixtime. All other inputs will be
interpreted by clock scan and converted to unix time. This task can be modified by subsequent
calls to this package's commands by referencing processname. If processname exists, it will be
replaced. If processname is not given, one is generated and returned by the command.

::cron::at start_coffee {Tomorrow at 9:00am} {remote::exec::coffeepot power on}
::cron::at shutdown_coffee {Tomorrow at 12:00pm} {remote::exec::coffeepot power off}

::cron::cancel processname
This command unregisters the process processname and cancels any pending commands. Note:
processname can be a process created by either ::cron::at or ::cron::every.

::cron::cancel check_mail

::cron::every processname frequency command
This command registers a command to be called at the interval of frequency. frequency is given in
seconds. This task can be modified by subsequent calls to this package's commands by referencing
processname. If processname exists, it will be replaced.

::cron::every check_mail 900 ::imap_client::check_mail
::cron::every backup_db 3600 {::backup_procedure ::mydb}

::cron::in ?processname? timecode command
This command registers a command to be called after a delay of time specified by timecode.
timecode is expressed as an seconds. This task can be modified by subsequent calls to this
package's commands by referencing processname. If processname exists, it will be replaced. If
processname is not given, one is generated and returned by the command.

::cron::object_coroutine object coroutine ?info?
This command registers a coroutine, associated with object to be called given the parameters of
info. If now parameters are given, the coroutine is assumed to be an idle task which will self-
terminate. info can be given in any form compadible with ::cron::task set

::cron::sleep milliseconds
When run within a coroutine, this command will register the coroutine for a callback at the
appointed time, and immediately yield.

If the ::cron::time variable is > 0 this command will advance the internal time, 100ms at a time.

In all other cases this command will generate a fictious variable, generate an after call, and
vwait the variable:

set eventid [incr ::cron::eventcount]
set var ::cron::event_#$eventid
set $var 0
::after $ms "set $var 1"
::vwait $var
::unset $var

Usage:

::cron::sleep 250

::cron::task delete process
Delete the process specified the process

::cron::task exists process
Returns true if process is registered with cron.

::cron::task info process
Returns a dict describing process. See ::cron::task set for a description of the options.

::cron::task set process field value ?field...? ?value...?

If process does not exist, it is created. Options Include:

command
If coroutine is black, a global command which implements this process. If coroutine is not
black, the command to invoke to create or recreate the coroutine.

coroutine
The name of the coroutine (if any) which implements this process.

frequency
If -1, this process is terminated after the next event. If 0 this process should be called
during every idle event. If positive, this process should generate events periodically. The
frequency is an integer number of milliseconds between events.

object The object associated with this process or coroutine.

scheduled
If non-zero, the absolute time from the epoch (in milliseconds) that this process will
trigger an event. If zero, and the frequency is also zero, this process is called every
idle loop.

running
A boolean flag. If true it indicates the process never returned or yielded during the event
loop, and will not be called again until it does so.

::cron::wake ?who?
Wake up cron, and arrange for its event loop to be run during the next Idle cycle.

::cron::wake {I just did something important}

Several utility commands are provided that are used internally within cron and for testing cron, but may
or may not be useful in the general cases.

::cron::clock_step milliseconds

Return a clock time absolute to the epoch which falls on the next border between one second and
the next for the value of milliseconds

::cron::clock_delay milliseconds

Return a clock time absolute to the epoch which falls on the next border between one second and
the next milliseconds in the future.

::cron::clock_sleep seconds ?offset?

Return a clock time absolute to the epoch which falls exactly seconds in the future. If offset is
given it may be positive or negative, and will shift the final time to before or after the second
would flip.

::cron::clock_set newtime

Sets the internal clock for cron. This command will advance the time in 100ms increment,
triggering events, until the internal time catches up with newtime.

newtime is expressed in absolute milliseconds since the beginning of the epoch.

BUGS, IDEAS, FEEDBACK

       This document, and the package it describes, will undoubtedly contain bugs and  other  problems.   Please
       report  such  in the category odie of the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist].  Please
       also report any ideas for enhancements you may have for either package and/or documentation.

       When proposing code changes, please provide unified diffs, i.e the output of diff -u.

       Note further that attachments are strongly preferred over inlined patches. Attachments  can  be  made  by
       going  to the Edit form of the ticket immediately after its creation, and then using the left-most button
       in the secondary navigation bar.

KEYWORDS

       cron, odie

COPYRIGHT

       Copyright (c) 2016-2018 Sean Woods <yoda@etoyoc.com>