plucky (3) Tcl_DeleteChannelHandler.3tcl.gz

NAME

       Tcl_CreateChannelHandler,  Tcl_DeleteChannelHandler - call a procedure when a channel becomes readable or
       writable

SYNOPSIS

       #include <tcl.h>

       Tcl_CreateChannelHandler(channel, mask, proc, clientData)

       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_ChannelProc *proc (in)               Procedure to invoke whenever the channel  indicated  by  channel
                                                meets the conditions specified by mask.

       void *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(
                      void *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