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OpenDarwin 7.2.1 - man page for tcl_deletechannelhandler (opendarwin section 3)

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_CreateChan-
						nel.

       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 temporar-
						ily disable an existing handler.

       Tcl_FileProc	 *proc	      (in)	Procedure to invoke whenever  the  channel  indi-
						cated  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  sub-
       set  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  client-
       Data.   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 channel, proc and client-
       Data; 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(3), Tcl_CreateChannel(3), Tcl_OpenFileChannel(3), vwait(n).

KEYWORDS
       blocking, callback, channel, events, handler, nonblocking.

Tcl					       7.5		      Tcl_CreateChannelHandler(3)


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