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Tcl_CreateFileHandler(3)    Tcl Library Procedures    Tcl_CreateFileHandler(3)


       Tcl_CreateFileHandler,   Tcl_DeleteFileHandler  -  associate  procedure
       callbacks with files or devices (Unix only)


       #include <tcl.h>

       Tcl_CreateFileHandler(fd, mask, proc, clientData)



       Unix file descriptor for an open  file  or  device.   Conditions  under
       which  proc  should  be  called:  OR-ed  combination  of  TCL_READABLE,
       TCL_WRITABLE, and TCL_EXCEPTION.  May be set to 0 to  temporarily  dis-
       able  a handler.  Procedure to invoke whenever the file or device indi-
       cated by file meets the conditions specified by mask.   Arbitrary  one-
       word value to pass to proc.


       Tcl_CreateFileHandler  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  TCL_READ-
       ABLE,  proc  will be called when the file is readable.  The callback to
       proc is made by Tcl_DoOneEvent, so Tcl_CreateFileHandler is only useful
       in  programs that dispatch events through Tcl_DoOneEvent or through Tcl
       commands such as vwait.

       Proc should have arguments and result that match the type Tcl_FileProc:
       typedef void Tcl_FileProc(
               ClientData clientData,
               int  mask);  The  clientData parameter to proc is a copy of the
       clientData argument given to Tcl_CreateFileHandler  when  the  callback
       was created.  Typically, clientData points to a data structure contain-
       ing application-specific information about the file.  Mask is an  inte-
       ger  mask  indicating which of the requested conditions actually exists
       for the file;  it will contain a subset of the bits in the  mask  argu-
       ment to Tcl_CreateFileHandler.

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

       Tcl_DeleteFileHandler 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

       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 will not be able to service
       other events. Use Tcl_SetChannelOption with -blocking to set the  chan-
       nel into blocking or nonblocking mode as required.

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


       callback, file, handler

Tcl                                   8.0             Tcl_CreateFileHandler(3)

CrtFileHdlr 8.5.4 - Generated Sun Aug 17 20:59:23 CDT 2008
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