Provided by: tcllib_1.19-dfsg-2_all 
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 milleseconds
::cron::clock_delay milleseconds
::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 interger number of
milleseconds between events. object The object associated with this process or coroutine.
scheduled If non-zero, the absolute time from the epoch (in milleseconds) 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 milleseconds
Return a clock time absolute to the epoch which falls on the next border between one second and
the next for the value of milleseconds
::cron::clock_delay milleseconds
Return a clock time absolute to the epoch which falls on the next border between one second and
the next milleseconds 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 milleseconds 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
CATEGORY
System
COPYRIGHT
Copyright (c) 2016-2018 Sean Woods <yoda@etoyoc.com>