Tcl_BackgroundException, Tcl_BackgroundError — report Tcl exception
that occurred in background processing
#include <tcl.h>
Tcl_BackgroundException(interp, code)
Tcl_BackgroundError(interp)
- Tcl_Interp *interp
(in)
- Interpreter in which the exception occurred.
- int code (in)
- The exceptional return code to be reported.
This procedure is typically invoked when a Tcl exception (any
return code other than TCL_OK) occurs during “background
processing” such as executing an event handler. When such an
exception occurs, the condition is reported to Tcl or to a widget
or some other C code, and there is not usually any obvious way for
that code to report the exception to the user. In these cases the
code calls Tcl_BackgroundException with an interp
argument identifying the interpreter in which the exception
occurred, and a code argument holding the return code value
of the exception. The state of the interpreter, including any error
message in the interpreter result, and the values of any entries in
the return options dictionary, is captured and saved.
Tcl_BackgroundException then arranges for the event loop to
invoke at some later time the command registered in that
interpreter to handle background errors by the interp bgerror command, passing the
captured values as arguments. The registered handler command is
meant to report the exception in an application-specific fashion.
The handler command receives two arguments, the result of the
interp, and the return options of the interp at the time the error
occurred. If the application registers no handler command, the
default handler command will attempt to call bgerror to report the error. If an
error condition arises while invoking the handler command, then
Tcl_BackgroundException reports the error itself by printing
a message on the standard error file.
Tcl_BackgroundException does not invoke the handler
command immediately because this could potentially interfere with
scripts that are in process at the time the error occurred.
Instead, it invokes the handler command later as an idle
callback.
It is possible for many background exceptions to accumulate
before the handler command is invoked. When this happens, each of
the exceptions is processed in order. However, if the handler
command returns a break exception, then all remaining error reports
for the interpreter are skipped.
The Tcl_BackgroundError routine is an older and simpler
interface useful when the exception code reported is TCL_ERROR. It is equivalent to:
Tcl_BackgroundException(interp, TCL_ERROR);
background, bgerror, error, interp
Copyright © 1992-1994 The Regents of the
University of California.
Copyright © 1994-1996 Sun Microsystems, Inc.