Tcl_CreateChannelHandler(3) Tcl Library Procedures Tcl_CreateChannelHandler(3)______________________________________________________________________________NAME
Tcl_CreateChannelHandler, Tcl_DeleteChannelHandler - call a procedure
when a channel becomes readable or writable
SYNOPSIS
#include <tcl.h>
void
Tcl_CreateChannelHandler(channel, mask, proc, clientData)
void
Tcl_DeleteChannelHandler(channel, proc, clientData)
ARGUMENTS
Tcl_Channel channel (in) Tcl channel such as returned
by Tcl_CreateChannel.
int mask (in) Conditions under which proc
should be called: OR-ed combi‐
nation of TCL_READABLE,
TCL_WRITABLE and TCL_EXCEP‐
TION. Specify a zero value to
temporarily disable an exist‐
ing handler.
Tcl_FileProc *proc (in) Procedure to invoke whenever
the channel indicated by chan‐
nel meets the conditions spec‐
ified by mask.
ClientData clientData (in) Arbitrary one-word value to
pass to proc.
_________________________________________________________________DESCRIPTION
Tcl_CreateChannelHandler arranges for proc to be called in the future
whenever input or output becomes possible on the channel identified by
channel, or whenever an exceptional condition exists for channel. The
conditions of interest under which proc will be invoked are specified
by the mask argument. See the manual entry for fileevent for a precise
description of what it means for a channel to be readable or writable.
Proc must conform to the following prototype:
typedef void Tcl_ChannelProc(
ClientData clientData,
int mask);
The clientData argument is the same as the value passed to Tcl_Create‐
ChannelHandler when the handler was created. Typically, clientData
points to a data structure containing application-specific information
about the channel. Mask is an integer mask indicating which of the
requested conditions actually exists for the channel; it will contain a
subset of the bits from the mask argument to Tcl_CreateChannelHandler
when the handler was created.
Each channel handler is identified by a unique combination of channel,
proc and clientData. There may be many handlers for a given channel as
long as they don't have the same channel, proc, and clientData. If
Tcl_CreateChannelHandler is invoked when there is already a handler for
channel, proc, and clientData, then no new handler is created;
instead, the mask is changed for the existing handler.
Tcl_DeleteChannelHandler deletes a channel handler identified by chan‐
nel, proc and clientData; if no such handler exists, the call has no
effect.
Channel handlers are invoked via the Tcl event mechanism, so they are
only useful in applications that are event-driven. Note also that the
conditions specified in the mask argument to proc may no longer exist
when proc is invoked: for example, if there are two handlers for
TCL_READABLE on the same channel, the first handler could consume all
of the available input so that the channel is no longer readable when
the second handler is invoked. For this reason it may be useful to use
nonblocking I/O on channels for which there are event handlers.
SEE ALSONotifier(3), Tcl_CreateChannel(3), Tcl_OpenFileChannel(3), vwait(n).
KEYWORDS
blocking, callback, channel, events, handler, nonblocking.
Tcl 7.5 Tcl_CreateChannelHandler(3)
