Tk_CreateErrorHandler(3Tk) Tk_CreateErrorHandler(3Tk)
Tk_CreateErrorHandler, Tk_DeleteErrorHandler - handle X protocol errors
#include <tk.h>
Tk_ErrorHandler
Tk_CreateErrorHandler(display, error, request, minor, proc, clientData)
Tk_DeleteErrorHandler(handler)
Display *display (in) Display whose errors are to be
handled.
int error (in) Match only error events with
this value in the error_code
field. If -1, then match any
error_code value.
int request (in) Match only error events with
this value in the request_code
field. If -1, then match any
request_code value.
int minor (in) Match only error events with
this value in the minor_code
field. If -1, then match any
minor_code value.
Tk_ErrorProc *proc (in) Procedure to invoke whenever an
error event is received for
display and matches error,
request, and minor. NULL means
ignore any matching errors.
ClientData clientData (in) Arbitrary one-word value to pass
to proc.
Tk_ErrorHandler handler (in) Token for error handler to
delete (return value from a
previous call to
Tk_CreateErrorHandler).
Tk_CreateErrorHandler arranges for a particular procedure (proc) to be
called whenever certain protocol errors occur on a particular display
(display). Protocol errors occur when the X protocol is used
incorrectly, such as attempting to map a window that doesn't exist. See
the Xlib documentation for XSetErrorHandler for more information on the
kinds of errors that can occur. For proc to be invoked to handle a
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Tk_CreateErrorHandler(3Tk) Tk_CreateErrorHandler(3Tk)
particular error, five things must occur:
[1] The error must pertain to display.
[2] Either the error argument to Tk_CreateErrorHandler must have been
-1, or the error argument must match the error_code field from the
error event.
[3] Either the request argument to Tk_CreateErrorHandler must have been
-1, or the request argument must match the request_code field from
the error event.
[4] Either the minor argument to Tk_CreateErrorHandler must have been
-1, or the minor argument must match the minor_code field from the
error event.
[5] The protocol request to which the error pertains must have been made
when the handler was active (see below for more information).
Proc should have arguments and result that match the following type:
typedef int Tk_ErrorProc(
ClientData clientData,
XErrorEvent *errEventPtr);
The clientData parameter to proc is a copy of the clientData argument
given to Tcl_CreateErrorHandler when the callback was created.
Typically, clientData points to a data structure containing applicationspecific
information that is needed to deal with the error. ErrEventPtr
is a pointer to the X error event. The procedure proc should return an
integer value. If it returns 0 it means that proc handled the error
completely and there is no need to take any other action for the error.
If it returns non-zero it means proc was unable to handle the error.
If a value of NULL is specified for proc, all matching errors will be
ignored: this will produce the same result as if a procedure had been
specified that always returns 0.
If more than more than one handler matches a particular error, then they
are invoked in turn. The handlers will be invoked in reverse order of
creation: most recently declared handler first. If any handler returns
0, then subsequent (older) handlers will not be invoked. If no handler
returns 0, then Tk invokes X'es default error handler, which prints an
error message and aborts the program. If you wish to have a default
handler that deals with errors that no other handler can deal with, then
declare it first.
The X documentation states that ``the error handler should not call any
functions (directly or indirectly) on the display that will generate
protocol requests or that will look for input events.'' This restriction
applies to handlers declared by Tk_CreateErrorHandler; disobey it at your
own risk.
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Tk_CreateErrorHandler(3Tk) Tk_CreateErrorHandler(3Tk)
Tk_DeleteErrorHandler may be called to delete a previously-created error
handler. The handler argument identifies the error handler, and should
be a value returned by a previous call to Tk_CreateEventHandler.
A particular error handler applies to errors resulting from protocol
requests generated between the call to Tk_CreateErrorHandler and the call
to Tk_DeleteErrorHandler. However, the actual callback to proc may not
occur until after the Tk_DeleteErrorHandler call, due to buffering in the
client and server. If an error event pertains to a protocol request made
just before calling Tk_DeleteErrorHandler, then the error event may not
have been processed before the Tk_DeleteErrorHandler call. When this
situation arises, Tk will save information about the handler and invoke
the handler's proc later when the error event finally arrives. If an
application wishes to delete an error handler and know for certain that
all relevant errors have been processed, it should first call
Tk_DeleteErrorHandler and then call XSync; this will flush out any
buffered requests and errors, but will result in a performance penalty
because it requires communication to and from the X server. After the
XSync call Tk is guaranteed not to call any error handlers deleted before
the XSync call.
For the Tk error handling mechanism to work properly, it is essential
that application code never calls XSetErrorHandler directly; applications
should use only Tk_CreateErrorHandler.
callback, error, event, handler
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