Tcl_BackgroundError(3tcl)				      Tcl Library Procedures					 Tcl_BackgroundError(3tcl)

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NAME

       Tcl_BackgroundError - report Tcl error that occurred in background processing

SYNOPSIS

       #include <tcl.h>

       Tcl_BackgroundError(interp)

ARGUMENTS

       Tcl_Interp *interp (in)		Interpreter in which the error occurred.
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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  message.	Tcl_BackgroundError will invoke the command registered in that interpreter to handle background errors by the interp bger-
       ror command.  The registered handler command is meant to report the error 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_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 handler command later as an idle callback.

       It is possible for many background errors to accumulate before the handler command is invoked.  When this happens, each of  the	errors	is
       processed  in  order.   However,  if the handle command returns a break exception, then all remaining error reports for the interpreter are
       skipped.

KEYWORDS

       background, bgerror, error, interp

Tcl									7.5						 Tcl_BackgroundError(3tcl)