1 | '\" |
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2 | '\" Copyright (c) 1998-1999 Scriptics Corporation |
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3 | '\" Copyright (c) 1995-1997 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: Notifier.3,v 1.21 2007/12/13 15:22:31 dgp Exp $ |
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9 | '\" |
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10 | .so man.macros |
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11 | .TH Notifier 3 8.1 Tcl "Tcl Library Procedures" |
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12 | .BS |
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13 | .SH NAME |
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14 | Tcl_CreateEventSource, Tcl_DeleteEventSource, Tcl_SetMaxBlockTime, Tcl_QueueEvent, Tcl_ThreadQueueEvent, Tcl_ThreadAlert, Tcl_GetCurrentThread, Tcl_DeleteEvents, Tcl_InitNotifier, Tcl_FinalizeNotifier, Tcl_WaitForEvent, Tcl_AlertNotifier, Tcl_SetTimer, Tcl_ServiceAll, Tcl_ServiceEvent, Tcl_GetServiceMode, Tcl_SetServiceMode \- the event queue and notifier interfaces |
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15 | .SH SYNOPSIS |
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16 | .nf |
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17 | \fB#include <tcl.h>\fR |
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18 | .sp |
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19 | void |
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20 | \fBTcl_CreateEventSource\fR(\fIsetupProc, checkProc, clientData\fR) |
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21 | .sp |
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22 | void |
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23 | \fBTcl_DeleteEventSource\fR(\fIsetupProc, checkProc, clientData\fR) |
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24 | .sp |
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25 | void |
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26 | \fBTcl_SetMaxBlockTime\fR(\fItimePtr\fR) |
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27 | .sp |
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28 | void |
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29 | \fBTcl_QueueEvent\fR(\fIevPtr, position\fR) |
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30 | .sp |
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31 | void |
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32 | \fBTcl_ThreadQueueEvent\fR(\fIthreadId, evPtr, position\fR) |
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33 | .sp |
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34 | void |
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35 | \fBTcl_ThreadAlert\fR(\fIthreadId\fR) |
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36 | .sp |
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37 | Tcl_ThreadId |
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38 | \fBTcl_GetCurrentThread\fR() |
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39 | .sp |
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40 | void |
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41 | \fBTcl_DeleteEvents\fR(\fIdeleteProc, clientData\fR) |
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42 | .sp |
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43 | ClientData |
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44 | \fBTcl_InitNotifier\fR() |
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45 | .sp |
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46 | void |
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47 | \fBTcl_FinalizeNotifier\fR(\fIclientData\fR) |
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48 | .sp |
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49 | int |
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50 | \fBTcl_WaitForEvent\fR(\fItimePtr\fR) |
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51 | .sp |
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52 | void |
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53 | \fBTcl_AlertNotifier\fR(\fIclientData\fR) |
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54 | .sp |
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55 | void |
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56 | \fBTcl_SetTimer\fR(\fItimePtr\fR) |
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57 | .sp |
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58 | int |
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59 | \fBTcl_ServiceAll\fR() |
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60 | .sp |
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61 | int |
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62 | \fBTcl_ServiceEvent\fR(\fIflags\fR) |
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63 | .sp |
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64 | int |
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65 | \fBTcl_GetServiceMode\fR() |
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66 | .sp |
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67 | int |
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68 | \fBTcl_SetServiceMode\fR(\fImode\fR) |
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69 | .sp |
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70 | void |
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71 | \fBTcl_ServiceModeHook\fR(\fImode\fR) |
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72 | .sp |
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73 | void |
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74 | \fBTcl_SetNotifier\fR(\fInotifierProcPtr\fR) |
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75 | .SH ARGUMENTS |
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76 | .AS Tcl_EventDeleteProc *notifierProcPtr |
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77 | .AP Tcl_EventSetupProc *setupProc in |
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78 | Procedure to invoke to prepare for event wait in \fBTcl_DoOneEvent\fR. |
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79 | .AP Tcl_EventCheckProc *checkProc in |
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80 | Procedure for \fBTcl_DoOneEvent\fR to invoke after waiting for |
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81 | events. Checks to see if any events have occurred and, if so, |
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82 | queues them. |
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83 | .AP ClientData clientData in |
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84 | Arbitrary one-word value to pass to \fIsetupProc\fR, \fIcheckProc\fR, or |
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85 | \fIdeleteProc\fR. |
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86 | .AP Tcl_Time *timePtr in |
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87 | Indicates the maximum amount of time to wait for an event. This |
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88 | is specified as an interval (how long to wait), not an absolute |
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89 | time (when to wakeup). If the pointer passed to \fBTcl_WaitForEvent\fR |
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90 | is NULL, it means there is no maximum wait time: wait forever if |
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91 | necessary. |
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92 | .AP Tcl_Event *evPtr in |
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93 | An event to add to the event queue. The storage for the event must |
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94 | have been allocated by the caller using \fBTcl_Alloc\fR or \fBckalloc\fR. |
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95 | .AP Tcl_QueuePosition position in |
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96 | Where to add the new event in the queue: \fBTCL_QUEUE_TAIL\fR, |
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97 | \fBTCL_QUEUE_HEAD\fR, or \fBTCL_QUEUE_MARK\fR. |
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98 | .AP Tcl_ThreadId threadId in |
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99 | A unique identifier for a thread. |
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100 | .AP Tcl_EventDeleteProc *deleteProc in |
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101 | Procedure to invoke for each queued event in \fBTcl_DeleteEvents\fR. |
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102 | .AP int flags in |
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103 | What types of events to service. These flags are the same as those |
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104 | passed to \fBTcl_DoOneEvent\fR. |
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105 | .AP int mode in |
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106 | Indicates whether events should be serviced by \fBTcl_ServiceAll\fR. |
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107 | Must be one of \fBTCL_SERVICE_NONE\fR or \fBTCL_SERVICE_ALL\fR. |
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108 | .AP Tcl_NotifierProcs* notifierProcPtr in |
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109 | Structure of function pointers describing notifier procedures that are |
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110 | to replace the ones installed in the executable. See |
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111 | \fBREPLACING THE NOTIFIER\fR for details. |
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112 | .BE |
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113 | |
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114 | .SH INTRODUCTION |
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115 | .PP |
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116 | The interfaces described here are used to customize the Tcl event |
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117 | loop. The two most common customizations are to add new sources of |
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118 | events and to merge Tcl's event loop with some other event loop, such |
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119 | as one provided by an application in which Tcl is embedded. Each of |
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120 | these tasks is described in a separate section below. |
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121 | .PP |
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122 | The procedures in this manual entry are the building blocks out of which |
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123 | the Tcl event notifier is constructed. The event notifier is the lowest |
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124 | layer in the Tcl event mechanism. It consists of three things: |
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125 | .IP [1] |
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126 | Event sources: these represent the ways in which events can be |
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127 | generated. For example, there is a timer event source that implements |
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128 | the \fBTcl_CreateTimerHandler\fR procedure and the \fBafter\fR |
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129 | command, and there is a file event source that implements the |
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130 | \fBTcl_CreateFileHandler\fR procedure on Unix systems. An event |
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131 | source must work with the notifier to detect events at the right |
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132 | times, record them on the event queue, and eventually notify |
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133 | higher-level software that they have occurred. The procedures |
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134 | \fBTcl_CreateEventSource\fR, \fBTcl_DeleteEventSource\fR, |
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135 | and \fBTcl_SetMaxBlockTime\fR, \fBTcl_QueueEvent\fR, and |
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136 | \fBTcl_DeleteEvents\fR are used primarily by event sources. |
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137 | .IP [2] |
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138 | The event queue: for non-threaded applications, |
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139 | there is a single queue for the whole application, |
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140 | containing events that have been detected but not yet serviced. Event |
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141 | sources place events onto the queue so that they may be processed in |
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142 | order at appropriate times during the event loop. The event queue |
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143 | guarantees a fair discipline of event handling, so that no event |
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144 | source can starve the others. It also allows events to be saved for |
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145 | servicing at a future time. Threaded applications work in a |
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146 | similar manner, except that there is a separate event queue for |
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147 | each thread containing a Tcl interpreter. |
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148 | \fBTcl_QueueEvent\fR is used (primarily |
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149 | by event sources) to add events to the event queue and |
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150 | \fBTcl_DeleteEvents\fR is used to remove events from the queue without |
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151 | processing them. In a threaded application, \fBTcl_QueueEvent\fR adds |
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152 | an event to the current thread's queue, and \fBTcl_ThreadQueueEvent\fR |
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153 | adds an event to a queue in a specific thread. |
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154 | .IP [3] |
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155 | The event loop: in order to detect and process events, the application |
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156 | enters a loop that waits for events to occur, places them on the event |
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157 | queue, and then processes them. Most applications will do this by |
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158 | calling the procedure \fBTcl_DoOneEvent\fR, which is described in a |
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159 | separate manual entry. |
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160 | .PP |
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161 | Most Tcl applications need not worry about any of the internals of |
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162 | the Tcl notifier. However, the notifier now has enough flexibility |
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163 | to be retargeted either for a new platform or to use an external event |
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164 | loop (such as the Motif event loop, when Tcl is embedded in a Motif |
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165 | application). The procedures \fBTcl_WaitForEvent\fR and |
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166 | \fBTcl_SetTimer\fR are normally implemented by Tcl, but may be |
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167 | replaced with new versions to retarget the notifier (the |
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168 | \fBTcl_InitNotifier\fR, \fBTcl_AlertNotifier\fR, |
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169 | \fBTcl_FinalizeNotifier\fR, \fBTcl_Sleep\fR, |
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170 | \fBTcl_CreateFileHandler\fR, and \fBTcl_DeleteFileHandler\fR must |
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171 | also be replaced; see CREATING A NEW NOTIFIER below for details). |
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172 | The procedures \fBTcl_ServiceAll\fR, \fBTcl_ServiceEvent\fR, |
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173 | \fBTcl_GetServiceMode\fR, and \fBTcl_SetServiceMode\fR are provided |
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174 | to help connect Tcl's event loop to an external event loop such as |
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175 | Motif's. |
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176 | .SH "NOTIFIER BASICS" |
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177 | .PP |
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178 | The easiest way to understand how the notifier works is to consider |
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179 | what happens when \fBTcl_DoOneEvent\fR is called. |
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180 | \fBTcl_DoOneEvent\fR is passed a \fIflags\fR argument that indicates |
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181 | what sort of events it is OK to process and also whether or not to |
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182 | block if no events are ready. \fBTcl_DoOneEvent\fR does the following |
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183 | things: |
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184 | .IP [1] |
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185 | Check the event queue to see if it contains any events that can |
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186 | be serviced. If so, service the first possible event, remove it |
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187 | from the queue, and return. It does this by calling |
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188 | \fBTcl_ServiceEvent\fR and passing in the \fIflags\fR argument. |
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189 | .IP [2] |
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190 | Prepare to block for an event. To do this, \fBTcl_DoOneEvent\fR |
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191 | invokes a \fIsetup procedure\fR in each event source. |
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192 | The event source will perform event-source specific initialization and |
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193 | possibly call \fBTcl_SetMaxBlockTime\fR to limit how long |
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194 | \fBTcl_WaitForEvent\fR will block if no new events occur. |
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195 | .IP [3] |
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196 | Call \fBTcl_WaitForEvent\fR. This procedure is implemented differently |
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197 | on different platforms; it waits for an event to occur, based on the |
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198 | information provided by the event sources. |
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199 | It may cause the application to block if \fItimePtr\fR specifies |
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200 | an interval other than 0. |
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201 | \fBTcl_WaitForEvent\fR returns when something has happened, |
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202 | such as a file becoming readable or the interval given by \fItimePtr\fR |
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203 | expiring. If there are no events for \fBTcl_WaitForEvent\fR to |
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204 | wait for, so that it would block forever, then it returns immediately |
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205 | and \fBTcl_DoOneEvent\fR returns 0. |
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206 | .IP [4] |
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207 | Call a \fIcheck procedure\fR in each event source. The check |
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208 | procedure determines whether any events of interest to this source |
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209 | occurred. If so, the events are added to the event queue. |
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210 | .IP [5] |
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211 | Check the event queue to see if it contains any events that can |
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212 | be serviced. If so, service the first possible event, remove it |
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213 | from the queue, and return. |
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214 | .IP [6] |
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215 | See if there are idle callbacks pending. If so, invoke all of them and |
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216 | return. |
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217 | .IP [7] |
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218 | Either return 0 to indicate that no events were ready, or go back to |
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219 | step [2] if blocking was requested by the caller. |
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220 | |
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221 | .SH "CREATING A NEW EVENT SOURCE" |
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222 | .PP |
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223 | An event source consists of three procedures invoked by the notifier, |
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224 | plus additional C procedures that are invoked by higher-level code |
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225 | to arrange for event-driven callbacks. The three procedures called |
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226 | by the notifier consist of the setup and check procedures described |
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227 | above, plus an additional procedure that is invoked when an event |
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228 | is removed from the event queue for servicing. |
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229 | .PP |
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230 | The procedure \fBTcl_CreateEventSource\fR creates a new event source. |
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231 | Its arguments specify the setup procedure and check procedure for |
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232 | the event source. |
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233 | \fISetupProc\fR should match the following prototype: |
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234 | .CS |
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235 | typedef void Tcl_EventSetupProc( |
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236 | ClientData \fIclientData\fR, |
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237 | int \fIflags\fR); |
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238 | .CE |
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239 | The \fIclientData\fR argument will be the same as the \fIclientData\fR |
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240 | argument to \fBTcl_CreateEventSource\fR; it is typically used to |
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241 | point to private information managed by the event source. |
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242 | The \fIflags\fR argument will be the same as the \fIflags\fR |
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243 | argument passed to \fBTcl_DoOneEvent\fR except that it will never |
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244 | be 0 (\fBTcl_DoOneEvent\fR replaces 0 with \fBTCL_ALL_EVENTS\fR). |
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245 | \fIFlags\fR indicates what kinds of events should be considered; |
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246 | if the bit corresponding to this event source is not set, the event |
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247 | source should return immediately without doing anything. For |
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248 | example, the file event source checks for the \fBTCL_FILE_EVENTS\fR |
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249 | bit. |
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250 | .PP |
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251 | \fISetupProc\fR's job is to make sure that the application wakes up |
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252 | when events of the desired type occur. This is typically done in a |
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253 | platform-dependent fashion. For example, under Unix an event source |
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254 | might call \fBTcl_CreateFileHandler\fR; under Windows it might |
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255 | request notification with a Windows event. For timer-driven event |
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256 | sources such as timer events or any polled event, the event source |
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257 | can call \fBTcl_SetMaxBlockTime\fR to force the application to wake |
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258 | up after a specified time even if no events have occurred. |
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259 | If no event source calls \fBTcl_SetMaxBlockTime\fR |
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260 | then \fBTcl_WaitForEvent\fR will wait as long as necessary for an |
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261 | event to occur; otherwise, it will only wait as long as the shortest |
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262 | interval passed to \fBTcl_SetMaxBlockTime\fR by one of the event |
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263 | sources. If an event source knows that it already has events ready to |
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264 | report, it can request a zero maximum block time. For example, the |
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265 | setup procedure for the X event source looks to see if there are |
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266 | events already queued. If there are, it calls |
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267 | \fBTcl_SetMaxBlockTime\fR with a 0 block time so that |
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268 | \fBTcl_WaitForEvent\fR does not block if there is no new data on the X |
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269 | connection. |
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270 | The \fItimePtr\fR argument to \fBTcl_WaitForEvent\fR points to |
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271 | a structure that describes a time interval in seconds and |
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272 | microseconds: |
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273 | .CS |
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274 | typedef struct Tcl_Time { |
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275 | long \fIsec\fR; |
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276 | long \fIusec\fR; |
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277 | } Tcl_Time; |
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278 | .CE |
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279 | The \fIusec\fR field should be less than 1000000. |
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280 | .PP |
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281 | Information provided to \fBTcl_SetMaxBlockTime\fR |
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282 | is only used for the next call to \fBTcl_WaitForEvent\fR; it is |
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283 | discarded after \fBTcl_WaitForEvent\fR returns. |
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284 | The next time an event wait is done each of the event sources' |
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285 | setup procedures will be called again, and they can specify new |
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286 | information for that event wait. |
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287 | .PP |
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288 | If the application uses an external event loop rather than |
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289 | \fBTcl_DoOneEvent\fR, the event sources may need to call |
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290 | \fBTcl_SetMaxBlockTime\fR at other times. For example, if a new event |
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291 | handler is registered that needs to poll for events, the event source |
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292 | may call \fBTcl_SetMaxBlockTime\fR to set the block time to zero to |
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293 | force the external event loop to call Tcl. In this case, |
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294 | \fBTcl_SetMaxBlockTime\fR invokes \fBTcl_SetTimer\fR with the shortest |
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295 | interval seen since the last call to \fBTcl_DoOneEvent\fR or |
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296 | \fBTcl_ServiceAll\fR. |
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297 | .PP |
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298 | In addition to the generic procedure \fBTcl_SetMaxBlockTime\fR, other |
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299 | platform-specific procedures may also be available for |
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300 | \fIsetupProc\fR, if there is additional information needed by |
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301 | \fBTcl_WaitForEvent\fR on that platform. For example, on Unix systems |
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302 | the \fBTcl_CreateFileHandler\fR interface can be used to wait for file events. |
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303 | .PP |
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304 | The second procedure provided by each event source is its check |
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305 | procedure, indicated by the \fIcheckProc\fR argument to |
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306 | \fBTcl_CreateEventSource\fR. \fICheckProc\fR must match the |
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307 | following prototype: |
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308 | .CS |
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309 | typedef void Tcl_EventCheckProc( |
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310 | ClientData \fIclientData\fR, |
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311 | int \fIflags\fR); |
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312 | .CE |
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313 | The arguments to this procedure are the same as those for \fIsetupProc\fR. |
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314 | \fBCheckProc\fR is invoked by \fBTcl_DoOneEvent\fR after it has waited |
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315 | for events. Presumably at least one event source is now prepared to |
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316 | queue an event. \fBTcl_DoOneEvent\fR calls each of the event sources |
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317 | in turn, so they all have a chance to queue any events that are ready. |
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318 | The check procedure does two things. First, it must see if any events |
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319 | have triggered. Different event sources do this in different ways. |
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320 | .PP |
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321 | If an event source's check procedure detects an interesting event, it |
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322 | must add the event to Tcl's event queue. To do this, the event source |
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323 | calls \fBTcl_QueueEvent\fR. The \fIevPtr\fR argument is a pointer to |
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324 | a dynamically allocated structure containing the event (see below for |
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325 | more information on memory management issues). Each event source can |
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326 | define its own event structure with whatever information is relevant |
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327 | to that event source. However, the first element of the structure |
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328 | must be a structure of type \fBTcl_Event\fR, and the address of this |
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329 | structure is used when communicating between the event source and the |
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330 | rest of the notifier. A \fBTcl_Event\fR has the following definition: |
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331 | .CS |
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332 | typedef struct { |
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333 | Tcl_EventProc *\fIproc\fR; |
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334 | struct Tcl_Event *\fInextPtr\fR; |
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335 | } Tcl_Event; |
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336 | .CE |
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337 | The event source must fill in the \fIproc\fR field of |
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338 | the event before calling \fBTcl_QueueEvent\fR. |
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339 | The \fInextPtr\fR is used to link together the events in the queue |
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340 | and should not be modified by the event source. |
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341 | .PP |
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342 | An event may be added to the queue at any of three positions, depending |
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343 | on the \fIposition\fR argument to \fBTcl_QueueEvent\fR: |
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344 | .IP \fBTCL_QUEUE_TAIL\fR 24 |
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345 | Add the event at the back of the queue, so that all other pending |
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346 | events will be serviced first. This is almost always the right |
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347 | place for new events. |
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348 | .IP \fBTCL_QUEUE_HEAD\fR 24 |
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349 | Add the event at the front of the queue, so that it will be serviced |
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350 | before all other queued events. |
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351 | .IP \fBTCL_QUEUE_MARK\fR 24 |
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352 | Add the event at the front of the queue, unless there are other |
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353 | events at the front whose position is \fBTCL_QUEUE_MARK\fR; if so, |
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354 | add the new event just after all other \fBTCL_QUEUE_MARK\fR events. |
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355 | This value of \fIposition\fR is used to insert an ordered sequence of |
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356 | events at the front of the queue, such as a series of |
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357 | Enter and Leave events synthesized during a grab or ungrab operation |
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358 | in Tk. |
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359 | .PP |
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360 | When it is time to handle an event from the queue (steps 1 and 4 |
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361 | above) \fBTcl_ServiceEvent\fR will invoke the \fIproc\fR specified |
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362 | in the first queued \fBTcl_Event\fR structure. |
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363 | \fIProc\fR must match the following prototype: |
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364 | .CS |
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365 | typedef int Tcl_EventProc( |
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366 | Tcl_Event *\fIevPtr\fR, |
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367 | int \fIflags\fR); |
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368 | .CE |
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369 | The first argument to \fIproc\fR is a pointer to the event, which will |
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370 | be the same as the first argument to the \fBTcl_QueueEvent\fR call that |
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371 | added the event to the queue. |
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372 | The second argument to \fIproc\fR is the \fIflags\fR argument for the |
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373 | current call to \fBTcl_ServiceEvent\fR; this is used by the event source |
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374 | to return immediately if its events are not relevant. |
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375 | .PP |
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376 | It is up to \fIproc\fR to handle the event, typically by invoking |
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377 | one or more Tcl commands or C-level callbacks. |
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378 | Once the event source has finished handling the event it returns 1 |
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379 | to indicate that the event can be removed from the queue. |
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380 | If for some reason the event source decides that the event cannot |
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381 | be handled at this time, it may return 0 to indicate that the event |
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382 | should be deferred for processing later; in this case \fBTcl_ServiceEvent\fR |
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383 | will go on to the next event in the queue and attempt to service it. |
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384 | There are several reasons why an event source might defer an event. |
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385 | One possibility is that events of this type are excluded by the |
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386 | \fIflags\fR argument. |
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387 | For example, the file event source will always return 0 if the |
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388 | \fBTCL_FILE_EVENTS\fR bit is not set in \fIflags\fR. |
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389 | Another example of deferring events happens in Tk if |
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390 | \fBTk_RestrictEvents\fR has been invoked to defer certain kinds |
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391 | of window events. |
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392 | .PP |
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393 | When \fIproc\fR returns 1, \fBTcl_ServiceEvent\fR will remove the |
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394 | event from the event queue and free its storage. |
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395 | Note that the storage for an event must be allocated by |
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396 | the event source (using \fBTcl_Alloc\fR or the Tcl macro \fBckalloc\fR) |
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397 | before calling \fBTcl_QueueEvent\fR, but it |
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398 | will be freed by \fBTcl_ServiceEvent\fR, not by the event source. |
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399 | .PP |
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400 | Threaded applications work in a |
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401 | similar manner, except that there is a separate event queue for |
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402 | each thread containing a Tcl interpreter. |
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403 | Calling \fBTcl_QueueEvent\fR in a multithreaded application adds |
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404 | an event to the current thread's queue. |
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405 | To add an event to another thread's queue, use \fBTcl_ThreadQueueEvent\fR. |
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406 | \fBTcl_ThreadQueueEvent\fR accepts as an argument a Tcl_ThreadId argument, |
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407 | which uniquely identifies a thread in a Tcl application. To obtain the |
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408 | Tcl_ThreadID for the current thread, use the \fBTcl_GetCurrentThread\fR |
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409 | procedure. (A thread would then need to pass this identifier to other |
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410 | threads for those threads to be able to add events to its queue.) |
---|
411 | After adding an event to another thread's queue, you then typically |
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412 | need to call \fBTcl_ThreadAlert\fR to |
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413 | .QW "wake up" |
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414 | that thread's notifier to alert it to the new event. |
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415 | .PP |
---|
416 | \fBTcl_DeleteEvents\fR can be used to explicitly remove one or more |
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417 | events from the event queue. \fBTcl_DeleteEvents\fR calls \fIproc\fR |
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418 | for each event in the queue, deleting those for with the procedure |
---|
419 | returns 1. Events for which the procedure returns 0 are left in the |
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420 | queue. \fIProc\fR should match the following prototype: |
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421 | .CS |
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422 | typedef int Tcl_EventDeleteProc( |
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423 | Tcl_Event *\fIevPtr\fR, |
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424 | ClientData \fIclientData\fR); |
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425 | .CE |
---|
426 | The \fIclientData\fR argument will be the same as the \fIclientData\fR |
---|
427 | argument to \fBTcl_DeleteEvents\fR; it is typically used to point to |
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428 | private information managed by the event source. The \fIevPtr\fR will |
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429 | point to the next event in the queue. |
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430 | .PP |
---|
431 | \fBTcl_DeleteEventSource\fR deletes an event source. The \fIsetupProc\fR, |
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432 | \fIcheckProc\fR, and \fIclientData\fR arguments must exactly match those |
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433 | provided to the \fBTcl_CreateEventSource\fR for the event source to be deleted. |
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434 | If no such source exists, \fBTcl_DeleteEventSource\fR has no effect. |
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435 | |
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436 | .SH "CREATING A NEW NOTIFIER" |
---|
437 | .PP |
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438 | The notifier consists of all the procedures described in this manual |
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439 | entry, plus \fBTcl_DoOneEvent\fR and \fBTcl_Sleep\fR, which are |
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440 | available on all platforms, and \fBTcl_CreateFileHandler\fR and |
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441 | \fBTcl_DeleteFileHandler\fR, which are Unix-specific. Most of these |
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442 | procedures are generic, in that they are the same for all notifiers. |
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443 | However, none of the procedures are notifier-dependent: |
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444 | \fBTcl_InitNotifier\fR, \fBTcl_AlertNotifier\fR, |
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445 | \fBTcl_FinalizeNotifier\fR, \fBTcl_SetTimer\fR, \fBTcl_Sleep\fR, |
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446 | \fBTcl_WaitForEvent\fR, \fBTcl_CreateFileHandler\fR, |
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447 | \fBTcl_DeleteFileHandler\fR and \fBTcl_ServiceModeHook\fR. To support a |
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448 | new platform or to integrate Tcl with an application-specific event loop, |
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449 | you must write new versions of these procedures. |
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450 | .PP |
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451 | \fBTcl_InitNotifier\fR initializes the notifier state and returns |
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452 | a handle to the notifier state. Tcl calls this |
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453 | procedure when initializing a Tcl interpreter. Similarly, |
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454 | \fBTcl_FinalizeNotifier\fR shuts down the notifier, and is |
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455 | called by \fBTcl_Finalize\fR when shutting down a Tcl interpreter. |
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456 | .PP |
---|
457 | \fBTcl_WaitForEvent\fR is the lowest-level procedure in the notifier; |
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458 | it is responsible for waiting for an |
---|
459 | .QW interesting |
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460 | event to occur or |
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461 | for a given time to elapse. Before \fBTcl_WaitForEvent\fR is invoked, |
---|
462 | each of the event sources' setup procedure will have been invoked. |
---|
463 | The \fItimePtr\fR argument to |
---|
464 | \fBTcl_WaitForEvent\fR gives the maximum time to block for an event, |
---|
465 | based on calls to \fBTcl_SetMaxBlockTime\fR made by setup procedures |
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466 | and on other information (such as the \fBTCL_DONT_WAIT\fR bit in |
---|
467 | \fIflags\fR). |
---|
468 | .PP |
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469 | Ideally, \fBTcl_WaitForEvent\fR should only wait for an event |
---|
470 | to occur; it should not actually process the event in any way. |
---|
471 | Later on, the |
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472 | event sources will process the raw events and create Tcl_Events on |
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473 | the event queue in their \fIcheckProc\fR procedures. |
---|
474 | However, on some platforms (such as Windows) this is not possible; |
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475 | events may be processed in \fBTcl_WaitForEvent\fR, including queuing |
---|
476 | Tcl_Events and more (for example, callbacks for native widgets may be |
---|
477 | invoked). The return value from \fBTcl_WaitForEvent\fR must be either |
---|
478 | 0, 1, or \-1. On platforms such as Windows where events get processed in |
---|
479 | \fBTcl_WaitForEvent\fR, a return value of 1 means that there may be more |
---|
480 | events still pending that have not been processed. This is a sign to the |
---|
481 | caller that it must call \fBTcl_WaitForEvent\fR again if it wants all |
---|
482 | pending events to be processed. A 0 return value means that calling |
---|
483 | \fBTcl_WaitForEvent\fR again will not have any effect: either this is a |
---|
484 | platform where \fBTcl_WaitForEvent\fR only waits without doing any event |
---|
485 | processing, or \fBTcl_WaitForEvent\fR knows for sure that there are no |
---|
486 | additional events to process (e.g. it returned because the time |
---|
487 | elapsed). Finally, a return value of \-1 means that the event loop is |
---|
488 | no longer operational and the application should probably unwind and |
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489 | terminate. Under Windows this happens when a WM_QUIT message is received; |
---|
490 | under Unix it happens when \fBTcl_WaitForEvent\fR would have waited |
---|
491 | forever because there were no active event sources and the timeout was |
---|
492 | infinite. |
---|
493 | .PP |
---|
494 | \fBTcl_AlertNotifier\fR is used in multithreaded applications to allow |
---|
495 | any thread to |
---|
496 | .QW "wake up" |
---|
497 | the notifier to alert it to new events on its |
---|
498 | queue. \fBTcl_AlertNotifier\fR requires as an argument the notifier |
---|
499 | handle returned by \fBTcl_InitNotifier\fR. |
---|
500 | .PP |
---|
501 | If the notifier will be used with an external event loop, then it must |
---|
502 | also support the \fBTcl_SetTimer\fR interface. \fBTcl_SetTimer\fR is |
---|
503 | invoked by \fBTcl_SetMaxBlockTime\fR whenever the maximum blocking |
---|
504 | time has been reduced. \fBTcl_SetTimer\fR should arrange for the |
---|
505 | external event loop to invoke \fBTcl_ServiceAll\fR after the specified |
---|
506 | interval even if no events have occurred. This interface is needed |
---|
507 | because \fBTcl_WaitForEvent\fR is not invoked when there is an external |
---|
508 | event loop. If the |
---|
509 | notifier will only be used from \fBTcl_DoOneEvent\fR, then |
---|
510 | \fBTcl_SetTimer\fR need not do anything. |
---|
511 | .PP |
---|
512 | \fBTcl_ServiceModeHook\fR is called by the platform-independent portion |
---|
513 | of the notifier when client code makes a call to |
---|
514 | \fBTcl_SetServiceMode\fR. This hook is provided to support operating |
---|
515 | systems that require special event handling when the application is in |
---|
516 | a modal loop (the Windows notifier, for instance, uses this hook to |
---|
517 | create a communication window). |
---|
518 | .PP |
---|
519 | On Unix systems, the file event source also needs support from the |
---|
520 | notifier. The file event source consists of the |
---|
521 | \fBTcl_CreateFileHandler\fR and \fBTcl_DeleteFileHandler\fR |
---|
522 | procedures, which are described in the \fBTcl_CreateFileHandler\fR |
---|
523 | manual page. |
---|
524 | .PP |
---|
525 | The \fBTcl_Sleep\fR and \fBTcl_DoOneEvent\fR interfaces are described |
---|
526 | in their respective manual pages. |
---|
527 | .PP |
---|
528 | The easiest way to create a new notifier is to look at the code |
---|
529 | for an existing notifier, such as the files \fBunix/tclUnixNotfy.c\fR |
---|
530 | or \fBwin/tclWinNotify.c\fR in the Tcl source distribution. |
---|
531 | |
---|
532 | .SH "REPLACING THE NOTIFIER" |
---|
533 | .PP |
---|
534 | A notifier that has been written according to the conventions above |
---|
535 | can also be installed in a running process in place of the standard |
---|
536 | notifier. This mechanism is used so that a single executable can be |
---|
537 | used (with the standard notifier) as a stand-alone program and reused |
---|
538 | (with a replacement notifier in a loadable extension) as an extension |
---|
539 | to another program, such as a Web browser plugin. |
---|
540 | .PP |
---|
541 | To do this, the extension makes a call to \fBTcl_SetNotifier\fR |
---|
542 | passing a pointer to a \fBTcl_NotifierProcs\fR data structure. The |
---|
543 | structure has the following layout: |
---|
544 | .CS |
---|
545 | typedef struct Tcl_NotifierProcs { |
---|
546 | Tcl_SetTimerProc *setTimerProc; |
---|
547 | Tcl_WaitForEventProc *waitForEventProc; |
---|
548 | Tcl_CreateFileHandlerProc *createFileHandlerProc; |
---|
549 | Tcl_DeleteFileHandlerProc *deleteFileHandlerProc; |
---|
550 | Tcl_InitNotifierProc *initNotifierProc; |
---|
551 | Tcl_FinalizeNotifierProc *finalizeNotifierProc; |
---|
552 | Tcl_AlertNotifierProc *alertNotifierProc; |
---|
553 | Tcl_ServiceModeHookProc *serviceModeHookProc; |
---|
554 | } Tcl_NotifierProcs; |
---|
555 | .CE |
---|
556 | Following the call to \fBTcl_SetNotifier\fR, the pointers given in |
---|
557 | the \fBTcl_NotifierProcs\fR structure replace whatever notifier had |
---|
558 | been installed in the process. |
---|
559 | .PP |
---|
560 | It is extraordinarily unwise to replace a running notifier. Normally, |
---|
561 | \fBTcl_SetNotifier\fR should be called at process initialization time |
---|
562 | before the first call to \fBTcl_InitNotifier\fR. |
---|
563 | |
---|
564 | .SH "EXTERNAL EVENT LOOPS" |
---|
565 | .PP |
---|
566 | The notifier interfaces are designed so that Tcl can be embedded into |
---|
567 | applications that have their own private event loops. In this case, |
---|
568 | the application does not call \fBTcl_DoOneEvent\fR except in the case |
---|
569 | of recursive event loops such as calls to the Tcl commands \fBupdate\fR |
---|
570 | or \fBvwait\fR. Most of the time is spent in the external event loop |
---|
571 | of the application. In this case the notifier must arrange for the |
---|
572 | external event loop to call back into Tcl when something |
---|
573 | happens on the various Tcl event sources. These callbacks should |
---|
574 | arrange for appropriate Tcl events to be placed on the Tcl event queue. |
---|
575 | .PP |
---|
576 | Because the external event loop is not calling \fBTcl_DoOneEvent\fR on |
---|
577 | a regular basis, it is up to the notifier to arrange for |
---|
578 | \fBTcl_ServiceEvent\fR to be called whenever events are pending on the |
---|
579 | Tcl event queue. The easiest way to do this is to invoke |
---|
580 | \fBTcl_ServiceAll\fR at the end of each callback from the external |
---|
581 | event loop. This will ensure that all of the event sources are |
---|
582 | polled, any queued events are serviced, and any pending idle handlers |
---|
583 | are processed before returning control to the application. In |
---|
584 | addition, event sources that need to poll for events can call |
---|
585 | \fBTcl_SetMaxBlockTime\fR to force the external event loop to call |
---|
586 | Tcl even if no events are available on the system event queue. |
---|
587 | .PP |
---|
588 | As a side effect of processing events detected in the main external |
---|
589 | event loop, Tcl may invoke \fBTcl_DoOneEvent\fR to start a recursive event |
---|
590 | loop in commands like \fBvwait\fR. \fBTcl_DoOneEvent\fR will invoke |
---|
591 | the external event loop, which will result in callbacks as described |
---|
592 | in the preceding paragraph, which will result in calls to |
---|
593 | \fBTcl_ServiceAll\fR. However, in these cases it is undesirable to |
---|
594 | service events in \fBTcl_ServiceAll\fR. Servicing events there is |
---|
595 | unnecessary because control will immediately return to the |
---|
596 | external event loop and hence to \fBTcl_DoOneEvent\fR, which can |
---|
597 | service the events itself. Furthermore, \fBTcl_DoOneEvent\fR is |
---|
598 | supposed to service only a single event, whereas \fBTcl_ServiceAll\fR |
---|
599 | normally services all pending events. To handle this situation, |
---|
600 | \fBTcl_DoOneEvent\fR sets a flag for \fBTcl_ServiceAll\fR |
---|
601 | that causes it to return without servicing any events. |
---|
602 | This flag is called the \fIservice mode\fR; |
---|
603 | \fBTcl_DoOneEvent\fR restores it to its previous value before it returns. |
---|
604 | .PP |
---|
605 | In some cases, however, it may be necessary for \fBTcl_ServiceAll\fR |
---|
606 | to service events |
---|
607 | even when it has been invoked from \fBTcl_DoOneEvent\fR. This happens |
---|
608 | when there is yet another recursive event loop invoked via an |
---|
609 | event handler called by \fBTcl_DoOneEvent\fR (such as one that is |
---|
610 | part of a native widget). In this case, \fBTcl_DoOneEvent\fR may not |
---|
611 | have a chance to service events so \fBTcl_ServiceAll\fR must service |
---|
612 | them all. Any recursive event loop that calls an external event |
---|
613 | loop rather than \fBTcl_DoOneEvent\fR must reset the service mode so |
---|
614 | that all events get processed in \fBTcl_ServiceAll\fR. This is done |
---|
615 | by invoking the \fBTcl_SetServiceMode\fR procedure. If |
---|
616 | \fBTcl_SetServiceMode\fR is passed \fBTCL_SERVICE_NONE\fR, then calls |
---|
617 | to \fBTcl_ServiceAll\fR will return immediately without processing any |
---|
618 | events. If \fBTcl_SetServiceMode\fR is passed \fBTCL_SERVICE_ALL\fR, |
---|
619 | then calls to \fBTcl_ServiceAll\fR will behave normally. |
---|
620 | \fBTcl_SetServiceMode\fR returns the previous value of the service |
---|
621 | mode, which should be restored when the recursive loop exits. |
---|
622 | \fBTcl_GetServiceMode\fR returns the current value of the service |
---|
623 | mode. |
---|
624 | |
---|
625 | .SH "SEE ALSO" |
---|
626 | \fBTcl_CreateFileHandler\fR, \fBTcl_DeleteFileHandler\fR, \fBTcl_Sleep\fR, |
---|
627 | \fBTcl_DoOneEvent\fR, \fBThread(3)\fR |
---|
628 | .SH KEYWORDS |
---|
629 | event, notifier, event queue, event sources, file events, timer, idle, service mode, threads |
---|