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 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.
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_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
existing handler.
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 is invoked. For this reason it may be useful to use nonblocking
I/O on channels for which there are event handlers.
SEE ALSO¶
Notifier(3tcl), Tcl_CreateChannel(3tcl), Tcl_OpenFileChannel(3tcl), vwait(3tcl).
KEYWORDS¶
blocking, callback, channel, events, handler, nonblocking.