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 bgerror Tcl
       command to report the error in an application-specific fashion.   If  no  bgerror  command
       exists,  or  if  it  returns with an error condition, then Tcl_BackgroundError reports the
       error itself by printing a message on the standard error file.

       Tcl_BackgroundError does not invoke bgerror immediately  because  this  could  potentially
       interfere  with  scripts  that are in process at the time the error occurred.  Instead, it
       invokes bgerror later as an idle callback.  Tcl_BackgroundError saves the  values  of  the
       errorInfo and errorCode variables and restores these values just before invoking bgerror.

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

KEYWORDS

       background, bgerror, error