Tcl_BackgroundError(3) Tcl Library Procedures Tcl_BackgroundError(3)______________________________________________________________________________NAMETcl_BackgroundError - report Tcl error that occurred in background pro‐
cessing
SYNOPSIS
#include <tcl.h>
Tcl_BackgroundError(interp)ARGUMENTS
Tcl_Interp *interp (in) Interpreter in which the error
occurred.
_________________________________________________________________DESCRIPTION
This procedure is typically invoked when a Tcl error occurs during
“background processing” such as executing an event handler. When such
an error occurs, the error 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 error to the user. In these cases the code calls
Tcl_BackgroundError with an interp argument identifying the interpreter
in which the error occurred. At the time Tcl_BackgroundError is
invoked, the interpreter's result is expected to contain an error mes‐
sage. Tcl_BackgroundError will invoke the command registered in that
interpreter to handle background errors by the interp bgerror command.
The registered handler command is meant to report the error in an
application-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_BackgroundError reports the error itself by
printing a message on the standard error file.
Tcl_BackgroundError 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 errors to accumulate before the han‐
dler command is invoked. When this happens, each of the errors is pro‐
cessed in order. However, if the handle command returns a break excep‐
tion, then all remaining error reports for the interpreter are skipped.
KEYWORDS
background, bgerror, error, interp
Tcl 7.5 Tcl_BackgroundError(3)
