NAME

       Tcl_CancelEval, Tcl_Canceled - cancel Tcl scripts

SYNOPSIS

       #include <tcl.h>
       int
       Tcl_CancelEval(interp, resultObjPtr, clientData, flags)

       int
       Tcl_Canceled(interp, flags)

ARGUMENTS

       Tcl_Interp *interp (in)          Interpreter in which to cancel the script.

       Tcl_Obj *resultObjPtr (in)       Error  message to use in the cancellation, or NULL to use
                                        a default message. If not NULL, this object will have its
                                        reference   count   decremented   before   Tcl_CancelEval
                                        returns.

       int flags (in)                   ORed combination of flag  bits  that  specify  additional
                                        options.   For  Tcl_CancelEval, only TCL_CANCEL_UNWIND is
                                        currently    supported.     For    Tcl_Canceled,     only
                                        TCL_LEAVE_ERR_MSG  and  TCL_CANCEL_UNWIND  are  currently
                                        supported.

       ClientData clientData (in)       Currently reserved for future use.  It should be  set  to
                                        NULL.
_________________________________________________________________________________________________

DESCRIPTION

       Tcl_CancelEval cancels or unwinds the script in progress soon after the next invocation of
       asynchronous handlers, causing TCL_ERROR to be the return  code  for  that  script.   This
       function is thread-safe and may be called from any thread in the process.

       Tcl_Canceled  checks  if the script in progress has been canceled and returns TCL_ERROR if
       it has.  Otherwise, TCL_OK is returned.  Extensions can use this function to check to  see
       if  they  should  abort a long running command.  This function is thread sensitive and may
       only be called from the thread the interpreter was created in.

   FLAG BITS
       Any ORed combination of the following values  may  be  used  for  the  flags  argument  to
       procedures such as Tcl_CancelEval:

       TCL_CANCEL_UNWIND   This   flag   is   used   by  Tcl_CancelEval  and  Tcl_Canceled.   For
                           Tcl_CancelEval, if this  flag  is  set,  the  script  in  progress  is
                           canceled and the evaluation stack for the interpreter is unwound.  For
                           Tcl_Canceled,  if  this  flag  is  set,  the  script  in  progress  is
                           considered  to  be  canceled  only  if  the  evaluation  stack for the
                           interpreter is being unwound.

       TCL_LEAVE_ERR_MSG   This flag is only  used  by  Tcl_Canceled;  it  is  ignored  by  other
                           procedures.   If  an  error  is returned and this bit is set in flags,
                           then an error message will be left in the interpreter's result,  where
                           it  can be retrieved with Tcl_GetObjResult or Tcl_GetStringResult.  If
                           this flag bit is not set  then  no  error  message  is  left  and  the
                           interpreter's result will not be modified.

SEE ALSO

       interp(3tcl), Tcl_Eval(3tcl), TIP 285

KEYWORDS

       cancel, unwind