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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.

  
void *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(


        void *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.






SEE ALSO


fileevent(3tcl), Tcl_CreateTimerHandler(3tcl),
    Tcl_DoWhenIdle(3tcl)






KEYWORDS


callback, file, handler







  

    8.0
    Tcl