Tcl_BackgroundError(3tcl) Tcl Library Procedures Tcl_BackgroundError(3tcl)
______________________________________________________________________________
NAME
Tcl_BackgroundException, Tcl_BackgroundError - report Tcl exception
that occurred in background processing
SYNOPSIS
#include <tcl.h>
Tcl_BackgroundException(interp, code)
Tcl_BackgroundError(interp)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter in which the exception oc-
curred.
int code (in) The exceptional return code to be re-
ported.
______________________________________________________________________________
DESCRIPTION
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 condi-
tion 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 ex-
ception. The state of the interpreter, including any error message in
the interpreter result, and the values of any entries in the return op-
tions 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 in-
terp bgerror command, passing the captured values as arguments. The
registered handler command is meant to report the exception in an ap-
plication-specific fashion. The handler command receives two argu-
ments, the result of the interp, and the return options of the interp
at the time the error occurred. If the application registers no han-
dler 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 han-
dler 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 use-
ful when the exception code reported is TCL_ERROR. It is equivalent
to:
Tcl_BackgroundException(interp, TCL_ERROR);
KEYWORDS
background, bgerror, error, interp
Tcl 7.5 Tcl_BackgroundError(3tcl)
Generated by dwww version 1.14 on Thu Jan 23 00:16:57 CET 2025.