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Tcl_BackgroundError(3)                     Tcl Library Procedures                     Tcl_BackgroundError(3)



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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 identi-fying identifying
       fying  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



Tcl                                                  7.5                              Tcl_BackgroundError(3)