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 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 fd, and the conditions of interest are indi
cated 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
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 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 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.
Note that these interfaces are only supported by the Unix |
implementation of the Tcl notifier.
KEYWORDS
callback, file, handler
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