TclCreateFileHandler(3) Tcl Library Procedures TclCreateFileHandler(3)

NAME
       TclCreateFileHandler,   TclDeleteFileHandler  -  associate  procedure
       callbacks with files or devices (Unix only)

SYNOPSIS
       ##iinncclluuddee <>

       TTccllCCrreeaatteeFFiilleeHHaannddlleerr(fd, mask, proc, clientData)                       |

       TTccllDDeelleetteeFFiilleeHHaannddlleerr(fd)                                               |

AARRGGUUMMEENNTTSS
       int            fd           (in)                                        ||
                                             Unix  file descriptor for an open |
                                             file or device.

       int            mask         (in)      Conditions   under   which   proc
                                             should  be called: OR-ed combina-
                                             tion       of       TTCCLLRREEAADDAABBLLEE,
                                             TTCCLLWWRRIITTAABBLLEE,  and TTCCLLEEXXCCEEPPTTIIOONN.
                                             May be set to  0  to  temporarily
                                             disable a handler.

       TclFileProc   *proc        (in)      Procedure  to invoke whenever the
                                             file or device indicated by  file
                                             meets the conditions specified by
                                             mask.

       ClientData     clientData   (in)      Arbitrary one-word value to  pass
                                             to proc.



DESCRIPTION
       TTccllCCrreeaatteeFFiilleeHHaannddlleerr  arranges  for  proc  to be invoked in the future |
       whenever I/O becomes possible on a file  or  an  exceptional  condition |
       exists  for  the file.  The file is indicated by fd, and the conditions |
       of interest are indicated by mask.  For example, if mask  is  TTCCLLRREEAADD-
       AABBLLEE,  proc  will be called when the file is readable.  The callback to
       proc is made by TTccllDDooOOnneeEEvveenntt, so TTccllCCrreeaatteeFFiilleeHHaannddlleerr is only useful
       in  programs that dispatch events through TTccllDDooOOnneeEEvveenntt or through Tcl
       commands such as vvwwaaiitt.

       Proc should have arguments and result that match the type TTccllFFiilleePPrroocc:
              typedef void TclFileProc(
                ClientData clientData,
                int mask);
       The  clientData  parameter to proc is a copy of the clientData argument
       given to TTccllCCrreeaatteeFFiilleeHHaannddlleerr when the callback  was  created.   Typi-
       cally,  clientData  points  to a data structure containing application-
       specific information about the file.  Mask is an integer mask  indicat-
       ing which of the requested conditions actually exists for the file;  it
       will contain a subset of the bits in the mask argument  to  TTccllCCrreeaattee-
       FFiilleeHHaannddlleerr.


       There  may exist only one handler for a given file at a given time.  If
       TTccllCCrreeaatteeFFiilleeHHaannddlleerr is called when a handler already exists  for  fd,
       then  the  new  callback  replaces  the information that was previously
       recorded.

       TTccllDDeelleetteeFFiilleeHHaannddlleerr may be called to delete the file handler for  fd;
       if no handler exists for the file given by fd then the procedure has no
       effect.

       The purpose of file handlers is to enable an application to respond  to
       events  while  waiting  for files to become ready for I/O.  For this to
       work correctly, the application may need to use non-blocking I/O opera-
       tions  on  the  files  for  which handlers are declared.  Otherwise the
       application may block if it reads or writes too much data; while  wait-
       ing  for  the  I/O to complete the application won't be able to service
       te eet. s TclSetChannelOption wt -blocking o e te  hn
       nel into blocking or nonblocking mode as required.

       Note  that  these interfaces are only supported by the Unix implementa- |
       tion of the Tcl notifier.


KKEEYYWWOORRDDSS
       callback, file, handler



Tcl                                   8.0             TclCreateFileHandler(3)