after(3tcl)
NAME
after - Execute a command after a time delay
SYNOPSIS
after ms after ms ?script script script ...? after cancel id after cancel script script script ... after idle ?script script script ...? after info ?id? ______________________________________________________________________________
DESCRIPTION
This command is used to delay execution of the program or to execute a
command in background sometime in the future. It has several forms,
depending on the first argument to the command:
after ms
Ms must be an integer giving a time in milliseconds. The
command sleeps for ms milliseconds and then returns. While the
command is sleeping the application does not respond to events.
after ms ?script script script ...?
In this form the command returns immediately, but it arranges
for a Tcl command to be executed ms milliseconds later as an
event handler. The command will be executed exactly once, at
the given time. The delayed command is formed by concatenating
all the script arguments in the same fashion as the concat
command. The command will be executed at global level (outside
the context of any Tcl procedure). If an error occurs while
executing the delayed command then the background error will be
reported by the command registered with interp bgerror. The
after command returns an identifier that can be used to cancel
the delayed command using after cancel.
after cancel id
Cancels the execution of a delayed command that was previously
scheduled. Id indicates which command should be canceled; it
must have been the return value from a previous after command.
If the command given by id has already been executed then the
after cancel command has no effect.
after cancel script script ...
This command also cancels the execution of a delayed command.
The script arguments are concatenated together with space
separators (just as in the concat command). If there is a
pending command that matches the string, it is cancelled and
will never be executed; if no such command is currently pending
then the after cancel command has no effect.
after idle script ?script script ...?
Concatenates the script arguments together with space separators
(just as in the concat command), and arranges for the resulting
script to be evaluated later as an idle callback. The script
will be run exactly once, the next time the event loop is
entered and there are no events to process. The command returns
an identifier that can be used to cancel the delayed command
using after cancel. If an error occurs while executing the
script then the background error will be reported by the command
registered with interp bgerror.
after info ?id?
This command returns information about existing event handlers.
If no id argument is supplied, the command returns a list of the
identifiers for all existing event handlers created by the after
command for this interpreter. If id is supplied, it specifies
an existing handler; id must have been the return value from
some previous call to after and it must not have triggered yet
or been cancelled. In this case the command returns a list with
two elements. The first element of the list is the script
associated with id, and the second element is either idle or
timer to indicate what kind of event handler it is.
The after ms and after idle forms of the command assume that the
application is event driven: the delayed commands will not be executed
unless the application enters the event loop. In applications that are
not normally event-driven, such as tclsh, the event loop can be entered
with the vwait and update commands.
EXAMPLES
This defines a command to make Tcl do nothing at all for N seconds:
proc sleep {N} {
after [expr {int($N * 1000)}]
}
This arranges for the command wake_up to be run in eight hours
(providing the event loop is active at that time):
after [expr {1000 * 60 * 60 * 8}] wake_up
The following command can be used to do long-running calculations (as
represented here by ::my_calc::one_step, which is assumed to return a
boolean indicating whether another step should be performed) in a step-
by-step fashion, though the calculation itself needs to be arranged so
it can work step-wise. This technique is extra careful to ensure that
the event loop is not starved by the rescheduling of processing steps
(arranging for the next step to be done using an already-triggered
timer event only when the event queue has been drained) and is useful
when you want to ensure that a Tk GUI remains responsive during a slow
task.
proc doOneStep {} {
if {[::my_calc::one_step]} {
after idle [list after 0 doOneStep]
}
}
doOneStep
SEE ALSO
concat(3tcl), interp(3tcl), update(3tcl), vwait(3tcl)
KEYWORDS
cancel, delay, idle callback, sleep, time
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
