94 lines
4.0 KiB
Plaintext
94 lines
4.0 KiB
Plaintext
'\"
|
|
'\" Copyright (c) 1990-1994 The Regents of the University of California.
|
|
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
|
|
'\"
|
|
'\" See the file "license.terms" for information on usage and redistribution
|
|
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
|
|
'\"
|
|
.TH bgerror n 7.5 Tcl "Tcl Built-In Commands"
|
|
.so man.macros
|
|
.BS
|
|
'\" Note: do not modify the .SH NAME line immediately below!
|
|
.SH NAME
|
|
bgerror \- Command invoked to process background errors
|
|
.SH SYNOPSIS
|
|
\fBbgerror \fImessage\fR
|
|
.BE
|
|
.SH DESCRIPTION
|
|
.PP
|
|
Release 8.5 of Tcl supports the \fBinterp bgerror\fR command,
|
|
which allows applications to register in an interpreter the command
|
|
that will handle background errors in that interpreter. In older
|
|
releases of Tcl, this level of control was not available, and applications
|
|
could control the handling of background errors only by creating
|
|
a command with the particular command name \fBbgerror\fR in the
|
|
global namespace of an interpreter. The following documentation
|
|
describes the interface requirements of the \fBbgerror\fR command
|
|
an application might define to retain compatibility with pre-8.5
|
|
releases of Tcl. Applications intending to support only
|
|
Tcl releases 8.5 and later should simply make use of \fBinterp bgerror\fR.
|
|
.PP
|
|
The \fBbgerror\fR command does not exist as built-in part of Tcl. Instead,
|
|
individual applications or users can define a \fBbgerror\fR
|
|
command (e.g. as a Tcl procedure) if they wish to handle background
|
|
errors.
|
|
.PP
|
|
A background error is one that occurs in an event handler or some
|
|
other command that did not originate with the application.
|
|
For example, if an error occurs while executing a command specified
|
|
with the \fBafter\fR command, then it is a background error.
|
|
For a non-background error, the error can simply be returned up
|
|
through nested Tcl command evaluations until it reaches the top-level
|
|
code in the application; then the application can report the error
|
|
in whatever way it wishes. When a background error occurs, the
|
|
unwinding ends in the Tcl library and there is no obvious way for Tcl
|
|
to report the error.
|
|
.PP
|
|
When Tcl detects a background error, it saves information about the
|
|
error and invokes a handler command registered by \fBinterp bgerror\fR
|
|
later as an idle event handler. The default handler command in turn
|
|
calls the \fBbgerror\fR command .
|
|
Before invoking \fBbgerror\fR, Tcl restores the
|
|
\fBerrorInfo\fR and \fBerrorCode\fR variables to their values at the
|
|
time the error occurred, then it invokes \fBbgerror\fR with the error
|
|
message as its only argument. Tcl assumes that the application has
|
|
implemented the \fBbgerror\fR command, and that the command will
|
|
report the error in a way that makes sense for the application. Tcl
|
|
will ignore any result returned by the \fBbgerror\fR command as long
|
|
as no error is generated.
|
|
.PP
|
|
If another Tcl error occurs within the \fBbgerror\fR command (for
|
|
example, because no \fBbgerror\fR command has been defined) then Tcl
|
|
reports the error itself by writing a message to stderr.
|
|
.PP
|
|
If several background errors accumulate before \fBbgerror\fR is
|
|
invoked to process them, \fBbgerror\fR will be invoked once for each
|
|
error, in the order they occurred. However, if \fBbgerror\fR returns
|
|
with a break exception, then any remaining errors are skipped without
|
|
calling \fBbgerror\fR.
|
|
.PP
|
|
If you are writing code that will be used by others as part of a
|
|
package or other kind of library, consider avoiding \fBbgerror\fR.
|
|
The reason for this is that the application programmer may also want
|
|
to define a \fBbgerror\fR, or use other code that does and thus will
|
|
have trouble integrating your code.
|
|
.SH "EXAMPLE"
|
|
.PP
|
|
This \fBbgerror\fR procedure appends errors to a file, with a timestamp.
|
|
.PP
|
|
.CS
|
|
proc bgerror {message} {
|
|
set timestamp [clock format [clock seconds]]
|
|
set fl [open mylog.txt {WRONLY CREAT APPEND}]
|
|
puts $fl "$timestamp: bgerror in $::argv '$message'"
|
|
close $fl
|
|
}
|
|
.CE
|
|
.SH "SEE ALSO"
|
|
after(n), errorCode(n), errorInfo(n), interp(n)
|
|
.SH KEYWORDS
|
|
background error, reporting
|
|
'\" Local Variables:
|
|
'\" mode: nroff
|
|
'\" End:
|