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Tcl_CreateFileHandler(3)                   Tcl Library Procedures                   Tcl_CreateFileHandler(3)



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

SYNOPSIS
       #include <tcl.h>

       Tcl_CreateFileHandler(fd, mask, proc, clientData)

       Tcl_DeleteFileHandler(fd)

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

       int mask (in)                         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 disable a handler.

       Tcl_FileProc *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.
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DESCRIPTION
       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  condi-tions conditions
       tions  of  interest are indicated by mask.  For example, if mask is TCL_READABLE, 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 containing applica-tion-specific application-specific
       tion-specific information about the file.  Mask is an integer mask indicating which of the  requested
       conditions  actually  exists for the file;  it will contain a subset of the bits in the mask argument
       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 recorded.

       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 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  operations on the files for which handlers are declared.  Otherwise the application may block if
       it reads or writes too much data; while waiting for the I/O to complete the application will  not  be
       able  to service other events. Use Tcl_SetChannelOption with -blocking to set the channel into block-ing blocking
       ing or nonblocking mode as required.

       Note that these interfaces are only supported by the Unix implementation of the Tcl notifier.


KEYWORDS
       callback, file, handler



Tcl                                                  8.0                            Tcl_CreateFileHandler(3)