NAME¶

timer - timer events for monotonic and wall clock time

SYNOPSIS¶

timer in delay unit script
timer at timepoint unit script
timer idle script
timer sleep for delay ?unit?
timer sleep until timepoint ?unit?
timer cancel id
timer info ?id?

DESCRIPTION¶

This command is used to delay execution of the program or to execute a command in background sometime in the future. Time may be specified by a monotonic time delay or by wall clock time point. It has the following methods:

timer in delay unit script

In this form the command returns immediately, but it arranges for a Tcl command to be executed after the given monotonic time delay elapsed as an event handler. The delay value is given in the specified unit. See TIME UNITS below for available units. The command will be executed exactly once, after the given time delay. The delayed command is given by the argument script. 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 command returns an identifier that can be used to cancel the delayed command using timer cancel or after cancel. A delay value of 0 (or negative) queues the event immediately with priority over other event types (if not installed with an event proc, which will wait for next round of events).

The command after ms script may also be used to register monotonic clock timer events.

Theey are handled by the same que as this form of the timer command.

timer at timepoint unit script

Same as timer in, but specifying a wall clock time point (epoc). A typical use-case is to pass result of a clock scan as time point. See example below.

Wall clock events have second priority after monotonic clock events.

If both fire the same instant, the monotonic clock command is always handled first.

timer idle script

Arranges for the 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 timer cancel or after cancel. If an error occurs while executing the script then the background error will be reported by the command registered with interp bgerror.

timer wait for delay ?unit?

delay must be a wide integer giving a time in the given unit (default: milliseconds). A negative number is treated as 0. The command sleeps for the given monotonic delay and then returns. While the command is sleeping the application does not respond to events.

timer wait until timepoint ?unit?

timepoint must be a wide integer giving a wall clock time point in the given unit (default: seconds). A negative number is treated as 0. The command sleeps (at least) until the given wall clock time point and then returns. While the command is sleeping the application does not respond to events.

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 timer or after command. If the command given by id has already been executed then the timer cancel command has no effect.

timer 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 timer and 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 timer or after and it must not have triggered yet or been canceled. In this case the command returns a list with two to three elements. The first element of the list is the script associated with id, and the second element is either idle, monotonic or wallclock to indicate what kind of event handler it is. A thierd list element is present for the kinds monotonic or wallclock. This element is the scheduled execution time point in microseconds of the given clock type.

The timer in, timer at and timer 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.

Note, that the output differs from after info.

TIME UNITS¶

Some forms of the command take a time unit. Available units are: us (for microseconds), microseconds, ms (for milliseconds), milliseconds, s (for seconds), seconds or any unique abbreviation.

TIME MAXIMUM VALUE¶

The arguments delay and timepoint are bound to a resulting 63 bit clock value (in unit microseconds). Any higher value (which is after year 294441) will result in a time to far error.

EXAMPLES¶

This arranges for the command wake_up to be run in eight hours wall clock time (providing the event loop is active at that time):

time at [clock add [clock seconds] 24 hours] seconds wake_up

SEE ALSO¶

concat(3tcl), interp(3tcl), timer(3tcl), update(3tcl), vwait(3tcl)

KEYWORDS¶

cancel, delay, idle callback, sleep, time