1Tcl_CreateChannelHandler(3) Tcl Library Procedures Tcl_CreateChannelHandler(3)
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6
8 Tcl_CreateChannelHandler, Tcl_DeleteChannelHandler - call a procedure
9 when a channel becomes readable or writable
10
12 #include <tcl.h>
13 void
15 Tcl_CreateChannelHandler(channel, mask, proc, clientData)
16 void
18 Tcl_DeleteChannelHandler(channel, proc, clientData)
19
22 Tcl_Channel channel (in) Tcl channel such as returned
23 by Tcl_CreateChannel.
24 int mask (in) Conditions under which proc
26 should be called: OR-ed combi‐
27 nation of TCL_READABLE,
28 TCL_WRITABLE and TCL_EXCEP‐
29 TION. Specify a zero value to
30 temporarily disable an exist‐
31 ing handler.
32 Tcl_FileProc *proc (in) Procedure to invoke whenever
34 the channel indicated by chan‐
35 nel meets the conditions spec‐
36 ified by mask.
37 ClientData clientData (in) Arbitrary one-word value to
39 pass to proc.
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41
43 Tcl_CreateChannelHandler arranges for proc to be called in the future
44 whenever input or output becomes possible on the channel identified by
45 channel, or whenever an exceptional condition exists for channel. The
46 conditions of interest under which proc will be invoked are specified
47 by the mask argument. See the manual entry for fileevent for a precise
48 description of what it means for a channel to be readable or writable.
49 Proc must conform to the following prototype:
50 typedef void Tcl_ChannelProc(
52 ClientData clientData,
53 int mask);
54 The clientData argument is the same as the value passed to Tcl_Create‐
56 ChannelHandler when the handler was created. Typically, clientData
57 points to a data structure containing application-specific information
58 about the channel. Mask is an integer mask indicating which of the
59 requested conditions actually exists for the channel; it will contain a
60 subset of the bits from the mask argument to Tcl_CreateChannelHandler
61 when the handler was created.
62 Each channel handler is identified by a unique combination of channel,
64 proc and clientData. There may be many handlers for a given channel as
65 long as they do not have the same channel, proc, and clientData. If
66 Tcl_CreateChannelHandler is invoked when there is already a handler for
67 channel, proc, and clientData, then no new handler is created;
68 instead, the mask is changed for the existing handler.
69 Tcl_DeleteChannelHandler deletes a channel handler identified by chan‐
71 nel, proc and clientData; if no such handler exists, the call has no
72 effect.
73 Channel handlers are invoked via the Tcl event mechanism, so they are
75 only useful in applications that are event-driven. Note also that the
76 conditions specified in the mask argument to proc may no longer exist
77 when proc is invoked: for example, if there are two handlers for
78 TCL_READABLE on the same channel, the first handler could consume all
79 of the available input so that the channel is no longer readable when
80 the second handler is invoked. For this reason it may be useful to use
81 nonblocking I/O on channels for which there are event handlers.
82
84 Notifier(3), Tcl_CreateChannel(3), Tcl_OpenFileChannel(3), vwait(n).
85
87 blocking, callback, channel, events, handler, nonblocking.
88Tcl 7.5 Tcl_CreateChannelHandler(3)