DOKK / manpages / debian 11 / tcl8.6-doc / Tcl_CreateChannelHandler.3tcl.en
Tcl_CreateChannelHandler(3tcl) Tcl Library Procedures Tcl_CreateChannelHandler(3tcl) 







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










#include <tcl.h>

void
Tcl_CreateChannelHandler(channel, mask, proc, clientData)

void
Tcl_DeleteChannelHandler(channel, proc, clientData)











  
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.
    
    

    

  










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.








Notifier(3tcl), Tcl_CreateChannel(3tcl),
    Tcl_OpenFileChannel(3tcl), vwait(3tcl).








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







  

    7.5
    Tcl