Tcl_CreateChannelHandler, Tcl_DeleteChannelHandler — call a procedure when a channel becomes readable or writable
- Tcl_CreateChannelHandler, Tcl_DeleteChannelHandler — call a procedure when a channel becomes readable or writable
- #include <tcl.h>
- Tcl_CreateChannelHandler(channel, mask, proc, clientData)
- Tcl_DeleteChannelHandler(channel, proc, clientData)
- SEE ALSO
Tcl_CreateChannelHandler(channel, mask, proc, clientData)
Tcl_DeleteChannelHandler(channel, proc, clientData)
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:
- Tcl_Channel channel (in)
Tcl channel such as returned by Tcl_CreateChannel.
- int mask (in)
Conditions under which proc should be called: OR-ed combination of
TCL_READABLE, TCL_WRITABLE and TCL_EXCEPTION. Specify
a zero value to temporarily disable an existing handler.
- Tcl_FileProc *proc (in)
Procedure to invoke whenever the channel indicated by channel meets
the conditions specified by mask.
- ClientData clientData (in)
Arbitrary one-word value to pass to proc.
typedef void Tcl_ChannelProc(
The clientData argument is the same as the value passed to
Tcl_CreateChannelHandler 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 do not
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
Tcl_DeleteChannelHandler deletes a channel handler identified by
channel, 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
For this reason it may be useful to use nonblocking I/O on channels
for which there are event handlers.
Notifier, Tcl_CreateChannel, Tcl_OpenFileChannel, vwait(n).
blocking, callback, channel, events, handler, nonblocking.
Copyright © 1996 Sun Microsystems, Inc.