Tcl_CreateFileHandler(Tcl Library ProceduTcl_CreateFileHandler(3)_________________________________________________________________NAME
Tcl_CreateFileHandler, Tcl_DeleteFileHandler - associate
procedure callbacks with files or devices
SYNOPSIS
#include <tcl.h>
Tcl_CreateFileHandler(file, mask, proc, clientData)
Tcl_DeleteFileHandler(file)ARGUMENTS
Tcl_File file (in) Generic file handle
for an open file or
device (such as
returned by Tcl_Get-
File call).
int mask (in) Conditions under
which proc should be
called: OR-ed combi-
nation of TCL_READ-
ABLE, 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 con-
ditions 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 file, 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 call-
back to proc is made by Tcl_DoOneEvent, so Tcl_CreateFile-
Handler is only useful in programs that dispatch events
through Tcl_DoOneEvent or through Tcl commands such as
vwait.
Tcl 7.5 1
Tcl_CreateFileHandler(Tcl Library ProceduTcl_CreateFileHandler(3)
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 client-
Data 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 file, then the new callback
replaces the information that was previously recorded.
Tcl_DeleteFileHandler may be called to delete the file
handler for file; if no handler exists for the file given
by file 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 applica-
tion 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
won't be able to service other events. Use Tcl_SetChan-
nelOption with -blocking to set the channel into blocking
or nonblocking mode as required.
KEYWORDS
callback, file, handler
Tcl 7.5 2
