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Tcl_CreateFileHandler(3tcl) Tcl Library Procedures Tcl_CreateFileHandler(3tcl)
 


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.
    
    

    
 

    

  




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 conditions 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 application-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 blocking or nonblocking mode as
  required.


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



KEYWORDS

callback, file, handler



  

    8.0
    Tcl