1 | '\" |
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2 | '\" Copyright (c) 1990-1994 The Regents of the University of California. |
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3 | '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. |
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4 | '\" |
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5 | '\" See the file "license.terms" for information on usage and redistribution |
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6 | '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. |
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7 | '\" |
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8 | '\" RCS: @(#) $Id: after.n,v 1.10 2007/12/13 15:22:32 dgp Exp $ |
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9 | '\" |
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10 | .so man.macros |
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11 | .TH after n 7.5 Tcl "Tcl Built-In Commands" |
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12 | .BS |
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13 | '\" Note: do not modify the .SH NAME line immediately below! |
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14 | .SH NAME |
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15 | after \- Execute a command after a time delay |
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16 | .SH SYNOPSIS |
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17 | \fBafter \fIms\fR |
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18 | .sp |
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19 | \fBafter \fIms \fR?\fIscript script script ...\fR? |
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20 | .sp |
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21 | \fBafter cancel \fIid\fR |
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22 | .sp |
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23 | \fBafter cancel \fIscript script script ...\fR |
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24 | .sp |
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25 | \fBafter idle \fR?\fIscript script script ...\fR? |
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26 | .sp |
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27 | \fBafter info \fR?\fIid\fR? |
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28 | .BE |
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29 | |
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30 | .SH DESCRIPTION |
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31 | .PP |
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32 | This command is used to delay execution of the program or to execute |
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33 | a command in background sometime in the future. It has several forms, |
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34 | depending on the first argument to the command: |
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35 | .TP |
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36 | \fBafter \fIms\fR |
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37 | \fIMs\fR must be an integer giving a time in milliseconds. |
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38 | The command sleeps for \fIms\fR milliseconds and then returns. |
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39 | While the command is sleeping the application does not respond to |
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40 | events. |
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41 | .TP |
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42 | \fBafter \fIms \fR?\fIscript script script ...\fR? |
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43 | In this form the command returns immediately, but it arranges |
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44 | for a Tcl command to be executed \fIms\fR milliseconds later as an |
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45 | event handler. |
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46 | The command will be executed exactly once, at the given time. |
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47 | The delayed command is formed by concatenating all the \fIscript\fR |
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48 | arguments in the same fashion as the \fBconcat\fR command. |
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49 | The command will be executed at global level (outside the context |
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50 | of any Tcl procedure). |
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51 | If an error occurs while executing the delayed command then |
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52 | the background error will be reported by the command |
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53 | registered with \fB interp bgerror\fR. |
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54 | The \fBafter\fR command returns an identifier that can be used |
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55 | to cancel the delayed command using \fBafter cancel\fR. |
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56 | .TP |
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57 | \fBafter cancel \fIid\fR |
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58 | Cancels the execution of a delayed command that |
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59 | was previously scheduled. |
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60 | \fIId\fR indicates which command should be canceled; it must have |
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61 | been the return value from a previous \fBafter\fR command. |
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62 | If the command given by \fIid\fR has already been executed then |
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63 | the \fBafter cancel\fR command has no effect. |
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64 | .TP |
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65 | \fBafter cancel \fIscript script ...\fR |
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66 | This command also cancels the execution of a delayed command. |
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67 | The \fIscript\fR arguments are concatenated together with space |
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68 | separators (just as in the \fBconcat\fR command). |
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69 | If there is a pending command that matches the string, it is |
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70 | cancelled and will never be executed; if no such command is |
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71 | currently pending then the \fBafter cancel\fR command has no effect. |
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72 | .TP |
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73 | \fBafter idle \fIscript \fR?\fIscript script ...\fR? |
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74 | Concatenates the \fIscript\fR arguments together with space |
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75 | separators (just as in the \fBconcat\fR command), and arranges |
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76 | for the resulting script to be evaluated later as an idle callback. |
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77 | The script will be run exactly once, the next time the event |
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78 | loop is entered and there are no events to process. |
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79 | The command returns an identifier that can be used |
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80 | to cancel the delayed command using \fBafter cancel\fR. |
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81 | If an error occurs while executing the script then the |
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82 | background error will be reported by the command |
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83 | registered with \fB interp bgerror\fR. |
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84 | .TP |
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85 | \fBafter info \fR?\fIid\fR? |
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86 | This command returns information about existing event handlers. |
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87 | If no \fIid\fR argument is supplied, the command returns |
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88 | a list of the identifiers for all existing |
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89 | event handlers created by the \fBafter\fR command for this |
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90 | interpreter. |
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91 | If \fIid\fR is supplied, it specifies an existing handler; |
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92 | \fIid\fR must have been the return value from some previous call |
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93 | to \fBafter\fR and it must not have triggered yet or been cancelled. |
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94 | In this case the command returns a list with two elements. |
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95 | The first element of the list is the script associated |
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96 | with \fIid\fR, and the second element is either |
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97 | \fBidle\fR or \fBtimer\fR to indicate what kind of event |
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98 | handler it is. |
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99 | .LP |
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100 | The \fBafter \fIms\fR and \fBafter idle\fR forms of the command |
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101 | assume that the application is event driven: the delayed commands |
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102 | will not be executed unless the application enters the event loop. |
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103 | In applications that are not normally event-driven, such as |
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104 | \fBtclsh\fR, the event loop can be entered with the \fBvwait\fR |
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105 | and \fBupdate\fR commands. |
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106 | .SH "EXAMPLES" |
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107 | This defines a command to make Tcl do nothing at all for \fIN\fR |
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108 | seconds: |
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109 | .CS |
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110 | proc sleep {N} { |
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111 | \fBafter\fR [expr {int($N * 1000)}] |
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112 | } |
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113 | .CE |
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114 | .PP |
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115 | This arranges for the command \fIwake_up\fR to be run in eight hours |
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116 | (providing the event loop is active at that time): |
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117 | .CS |
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118 | \fBafter\fR [expr {1000 * 60 * 60 * 8}] wake_up |
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119 | .CE |
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120 | .PP |
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121 | The following command can be used to do long-running calculations (as |
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122 | represented here by \fI::my_calc::one_step\fR, which is assumed to |
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123 | return a boolean indicating whether another step should be performed) |
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124 | in a step-by-step fashion, though the calculation itself needs to be |
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125 | arranged so it can work step-wise. This technique is extra careful to |
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126 | ensure that the event loop is not starved by the rescheduling of |
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127 | processing steps (arranging for the next step to be done using an |
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128 | already-triggered timer event only when the event queue has been |
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129 | drained) and is useful when you want to ensure that a Tk GUI remains |
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130 | responsive during a slow task. |
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131 | .CS |
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132 | proc doOneStep {} { |
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133 | if {[::my_calc::one_step]} { |
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134 | \fBafter idle\fR [list \fBafter\fR 0 doOneStep] |
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135 | } |
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136 | } |
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137 | doOneStep |
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138 | .CE |
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139 | |
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140 | .SH "SEE ALSO" |
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141 | concat(n), interp(n), update(n), vwait(n) |
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142 | |
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143 | .SH KEYWORDS |
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144 | cancel, delay, idle callback, sleep, time |
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