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 bgerror  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