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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 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 regis-
       tered 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 fash-
       ion.  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_Back-
       groundError 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  inter-
       preter are skipped.

KEYWORDS
       background, bgerror, error, interp

Tcl					       7.5			   Tcl_BackgroundError(3)
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