Tcl_CreateFileHandler(3) Tcl Library Procedures Tcl_CreateFileHandler(3)______________________________________________________________________________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 combina‐
tion 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.
_________________________________________________________________DESCRIPTIONTcl_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. 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 Tcl_Create‐
FileHandler.
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 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.
KEYWORDS
callback, file, handler
Tcl 8.0 Tcl_CreateFileHandler(3)
