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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26 This command is used to delay execution of the program or to execute a
27 command in background sometime in the future. It has several forms,
28 depending on the first argument to the command:
29 after ms
31 Ms must be an integer giving a time in milliseconds. The com‐
32 mand sleeps for ms milliseconds and then returns. While the
33 command is sleeping the application does not respond to events.
34 after ms ?script script script ...?
36 In this form the command returns immediately, but it arranges
37 for a Tcl command to be executed ms milliseconds later as an
38 event handler. The command will be executed exactly once, at
39 the given time. The delayed command is formed by concatenating
40 all the script arguments in the same fashion as the concat com‐
41 mand. The command will be executed at global level (outside the
42 context of any Tcl procedure). If an error occurs while execut‐
43 ing the delayed command then the bgerror mechanism is used to
44 report the error. The after command returns an identifier that
45 can be used to cancel 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 cancelled 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 bgerror mechanism is used to report the error.
71 after info ?id?
73 This command returns information about existing event handlers.
74 If no id argument is supplied, the command returns a list of the
75 identifiers for all existing event handlers created by the after
76 command for this interpreter. If id is supplied, it specifies
77 an existing handler; id must have been the return value from
78 some previous call to after and it must not have triggered yet
79 or been cancelled. In this case the command returns a list with
80 two elements. The first element of the list is the script asso‐
81 ciated with id, and the second element is either idle or timer
82 to indicate what kind of event handler it is.
83 The after ms and after idle forms of the command assume that the appli‐
85 cation is event driven: the delayed commands will not be executed
86 unless the application enters the event loop. In applications that are
87 not normally event-driven, such as tclsh, the event loop can be entered
88 with the vwait and update commands.
89
91 This defines a command to make Tcl do nothing at all for N seconds:
92 proc sleep {N} {
93 after [expr {int($N * 1000)}]
94 }
95 This arranges for the command wake_up to be run in eight hours (provid‐
97 ing the event loop is active at that time):
98 after [expr {1000 * 60 * 60 * 8}] wake_up
99 The following command can be used to do long-running calculations (as
101 represented here by ::my_calc::one_step, which is assumed to return a
102 boolean indicating whether another step should be performed) in a step-
103 by-step fashion, though the calculation itself needs to be arranged so
104 it can work step-wise. This technique is extra careful to ensure that
105 the event loop is not starved by the rescheduling of processing steps
106 (arranging for the next step to be done using an already-triggered
107 timer event only when the event queue has been drained) and is useful
108 when you want to ensure that a Tk GUI remains responsive during a slow
109 task.
110 proc doOneStep {} {
111 if {[::my_calc::one_step]} {
112 after idle [list after 0 doOneStep]
113 }
114 }
115 doOneStep
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119 bgerror(n), concat(n), update(n), vwait(n)
120
123 cancel, delay, idle callback, sleep, time
124Tcl 7.5 after(n)