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diff --git a/tcl8.6/doc/bgerror.n b/tcl8.6/doc/bgerror.n new file mode 100644 index 0000000..3644b3d --- /dev/null +++ b/tcl8.6/doc/bgerror.n @@ -0,0 +1,93 @@ +'\" +'\" 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: |