1after(n) Tcl Built-In Commands after(n)
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8 after - Execute a command after a time delay
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11 after ms
12 after ms ?script script script ...?
14 after cancel id
16 after cancel script script script ...
18 after idle ?script script script ...?
20 after info ?id?
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25 This command is used to delay execution of the program or to execute a
26 command in background sometime in the future. It has several forms,
27 depending on the first argument to the command:
28 after ms
30 Ms must be an integer giving a time in milliseconds. The com‐
31 mand sleeps for ms milliseconds and then returns. While the
32 command is sleeping the application does not respond to events.
33 after ms ?script script script ...?
35 In this form the command returns immediately, but it arranges
36 for a Tcl command to be executed ms milliseconds later as an
37 event handler. The command will be executed exactly once, at
38 the given time. The delayed command is formed by concatenating
39 all the script arguments in the same fashion as the concat com‐
40 mand. The command will be executed at global level (outside the
41 context of any Tcl procedure). If an error occurs while execut‐
42 ing the delayed command then the background error will be
43 reported by the command registered with interp bgerror. The
44 after command returns an identifier that can be used to cancel
45 the delayed command using after cancel.
46 after cancel id
48 Cancels the execution of a delayed command that was previously
49 scheduled. Id indicates which command should be canceled; it
50 must have been the return value from a previous after command.
51 If the command given by id has already been executed then the
52 after cancel command has no effect.
53 after cancel script script ...
55 This command also cancels the execution of a delayed command.
56 The script arguments are concatenated together with space sepa‐
57 rators (just as in the concat command). If there is a pending
58 command that matches the string, it is canceled and will never
59 be executed; if no such command is currently pending then the
60 after cancel command has no effect.
61 after idle script ?script script ...?
63 Concatenates the script arguments together with space separators
64 (just as in the concat command), and arranges for the resulting
65 script to be evaluated later as an idle callback. The script
66 will be run exactly once, the next time the event loop is
67 entered and there are no events to process. The command returns
68 an identifier that can be used to cancel the delayed command
69 using after cancel. If an error occurs while executing the
70 script then the background error will be reported by the command
71 registered with interp bgerror.
72 after info ?id?
74 This command returns information about existing event handlers.
75 If no id argument is supplied, the command returns a list of the
76 identifiers for all existing event handlers created by the after
77 command for this interpreter. If id is supplied, it specifies
78 an existing handler; id must have been the return value from
79 some previous call to after and it must not have triggered yet
80 or been canceled. In this case the command returns a list with
81 two elements. The first element of the list is the script asso‐
82 ciated with id, and the second element is either idle or timer
83 to indicate what kind of event handler it is.
84 The after ms and after idle forms of the command assume that the appli‐
86 cation is event driven: the delayed commands will not be executed
87 unless the application enters the event loop. In applications that are
88 not normally event-driven, such as tclsh, the event loop can be entered
89 with the vwait and update commands.
90
92 This defines a command to make Tcl do nothing at all for N seconds:
93 proc sleep {N} {
95 after [expr {int($N * 1000)}]
96 }
97 This arranges for the command wake_up to be run in eight hours (provid‐
99 ing the event loop is active at that time):
100 after [expr {1000 * 60 * 60 * 8}] wake_up
102 The following command can be used to do long-running calculations (as
104 represented here by ::my_calc::one_step, which is assumed to return a
105 boolean indicating whether another step should be performed) in a step-
106 by-step fashion, though the calculation itself needs to be arranged so
107 it can work step-wise. This technique is extra careful to ensure that
108 the event loop is not starved by the rescheduling of processing steps
109 (arranging for the next step to be done using an already-triggered
110 timer event only when the event queue has been drained) and is useful
111 when you want to ensure that a Tk GUI remains responsive during a slow
112 task.
113 proc doOneStep {} {
115 if {[::my_calc::one_step]} {
116 after idle [list after 0 doOneStep]
117 }
118 }
119 doOneStep
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122 concat(n), interp(n), update(n), vwait(n)
123
125 cancel, delay, idle callback, sleep, time
126Tcl 7.5 after(n)