1Tk_CreateErrorHandler(3) Tk Library Procedures Tk_CreateErrorHandler(3)
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8 Tk_CreateErrorHandler, Tk_DeleteErrorHandler - handle X protocol errors
9
11 #include <tk.h>
12 Tk_ErrorHandler
14 Tk_CreateErrorHandler(display, error, request, minor, proc, clientData)
15 Tk_DeleteErrorHandler(handler)
17
19 Display *display (in) Display whose errors are to be
20 handled.
21 int error (in) Match only error events with
23 this value in the error_code
24 field. If -1, then match any
25 error_code value.
26 int request (in) Match only error events with
28 this value in the request_code
29 field. If -1, then match any
30 request_code value.
31 int minor (in) Match only error events with
33 this value in the minor_code
34 field. If -1, then match any
35 minor_code value.
36 Tk_ErrorProc *proc (in) Procedure to invoke whenever
38 an error event is received for
39 display and matches error,
40 request, and minor. NULL
41 means ignore any matching
42 errors.
43 ClientData clientData (in) Arbitrary one-word value to
45 pass to proc.
46 Tk_ErrorHandler handler (in) Token for error handler to
48 delete (return value from a
49 previous call to Tk_CreateEr‐
50 rorHandler).
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52
54 Tk_CreateErrorHandler arranges for a particular procedure (proc) to be
55 called whenever certain protocol errors occur on a particular display
56 (display). Protocol errors occur when the X protocol is used incor‐
57 rectly, such as attempting to map a window that does not exist. See
58 the Xlib documentation for XSetErrorHandler for more information on the
59 kinds of errors that can occur. For proc to be invoked to handle a
60 particular error, five things must occur:
61 [1] The error must pertain to display.
63 [2] Either the error argument to Tk_CreateErrorHandler must have
65 been -1, or the error argument must match the error_code field
66 from the error event.
67 [3] Either the request argument to Tk_CreateErrorHandler must have
69 been -1, or the request argument must match the request_code
70 field from the error event.
71 [4] Either the minor argument to Tk_CreateErrorHandler must have
73 been -1, or the minor argument must match the minor_code field
74 from the error event.
75 [5] The protocol request to which the error pertains must have been
77 made when the handler was active (see below for more informa‐
78 tion).
79 Proc should have arguments and result that match the following type:
81 typedef int Tk_ErrorProc(
82 ClientData clientData,
83 XErrorEvent *errEventPtr);
84 The clientData parameter to proc is a copy of the clientData argument
85 given to Tcl_CreateErrorHandler when the callback was created. Typi‐
86 cally, clientData points to a data structure containing application-
87 specific information that is needed to deal with the error.
88 ErrEventPtr is a pointer to the X error event. The procedure proc
89 should return an integer value. If it returns 0 it means that proc
90 handled the error completely and there is no need to take any other
91 action for the error. If it returns non-zero it means proc was unable
92 to handle the error.
93 If a value of NULL is specified for proc, all matching errors will be
95 ignored: this will produce the same result as if a procedure had been
96 specified that always returns 0.
97 If more than more than one handler matches a particular error, then
99 they are invoked in turn. The handlers will be invoked in reverse
100 order of creation: most recently declared handler first. If any han‐
101 dler returns 0, then subsequent (older) handlers will not be invoked.
102 If no handler returns 0, then Tk invokes X's default error handler,
103 which prints an error message and aborts the program. If you wish to
104 have a default handler that deals with errors that no other handler can
105 deal with, then declare it first.
106 The X documentation states that “the error handler should not call any
108 functions (directly or indirectly) on the display that will generate
109 protocol requests or that will look for input events.” This restric‐
110 tion applies to handlers declared by Tk_CreateErrorHandler; disobey it
111 at your own risk.
112 Tk_DeleteErrorHandler may be called to delete a previously-created
114 error handler. The handler argument identifies the error handler, and
115 should be a value returned by a previous call to Tk_CreateEventHandler.
116 A particular error handler applies to errors resulting from protocol
118 requests generated between the call to Tk_CreateErrorHandler and the
119 call to Tk_DeleteErrorHandler. However, the actual callback to proc
120 may not occur until after the Tk_DeleteErrorHandler call, due to
121 buffering in the client and server. If an error event pertains to a
122 protocol request made just before calling Tk_DeleteErrorHandler, then
123 the error event may not have been processed before the Tk_DeleteEr‐
124 rorHandler call. When this situation arises, Tk will save information
125 about the handler and invoke the handler's proc later when the error
126 event finally arrives. If an application wishes to delete an error
127 handler and know for certain that all relevant errors have been pro‐
128 cessed, it should first call Tk_DeleteErrorHandler and then call XSync;
129 this will flush out any buffered requests and errors, but will result
130 in a performance penalty because it requires communication to and from
131 the X server. After the XSync call Tk is guaranteed not to call any
132 error handlers deleted before the XSync call.
133 For the Tk error handling mechanism to work properly, it is essential
135 that application code never calls XSetErrorHandler directly; applica‐
136 tions should use only Tk_CreateErrorHandler.
137
139 callback, error, event, handler
140Tk Tk_CreateErrorHandler(3)