notifier.3

linux系统下的音频通信

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'\" Copyright (c) 1995-1997 Sun Microsystems, Inc.
'\"
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'\" SCCS: @(#) Notifier.3 1.16 97/05/17 17:03:17
'\" 
.so man.macros
.TH Notifier 3 8.0 Tcl "Tcl Library Procedures"
.BS
.VS
.SH NAME
Tcl_CreateEventSource, Tcl_DeleteEventSource, Tcl_SetMaxBlockTime, Tcl_QueueEvent, Tcl_DeleteEvents, Tcl_WaitForEvent, Tcl_SetTimer, Tcl_ServiceAll, Tcl_ServiceEvent, Tcl_GetServiceMode, Tcl_SetServiceMode \- the event queue and notifier interfaces

.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
\fBTcl_CreateEventSource\fR(\fIsetupProc, checkProc, clientData\fB)\fR
.sp
\fBTcl_DeleteEventSource\fR(\fIsetupProc, checkProc, clientData\fB)\fR
.sp
\fBTcl_SetMaxBlockTime\fR(\fItimePtr\fB)\fR
.sp
\fBTcl_QueueEvent\fR(\fIevPtr, position\fR)
.VS
.sp
\fBTcl_DeleteEvents\fR(\fIdeleteProc, clientData\fR)
.sp
int
\fBTcl_WaitForEvent\fR(\fItimePtr\fR)
.sp
\fBTcl_SetTimer\fR(\fItimePtr\fR)
.sp
int
\fBTcl_ServiceAll\fR()
.sp
int
\fBTcl_ServiceEvent\fR(\fIflags\fR)
.sp
int
\fBTcl_GetServiceMode\fR()
.sp
int		
\fBTcl_SetServiceMode\fR(\fImode\fR)
.VE

.SH ARGUMENTS
.AS Tcl_EventDeleteProc milliseconds
.AS Tcl_EventSetupProc *setupProc
.AP Tcl_EventSetupProc *setupProc in
Procedure to invoke to prepare for event wait in \fBTcl_DoOneEvent\fR.
.AP Tcl_EventCheckProc *checkProc in
Procedure for \fBTcl_DoOneEvent\fR to invoke after waiting for
events.  Checks to see if any events have occurred and, if so,
queues them.
.AP ClientData clientData in
Arbitrary one-word value to pass to \fIsetupProc\fR, \fIcheckProc\fR, or
\fIdeleteProc\fR.
.AP Tcl_Time *timePtr in
Indicates the maximum amount of time to wait for an event.  This
is specified as an interval (how long to wait), not an absolute
time (when to wakeup).  If the pointer passed to \fBTcl_WaitForEvent\fR
is NULL, it means there is no maximum wait time:  wait forever if
necessary.
.AP Tcl_Event *evPtr in
An event to add to the event queue.  The storage for the event must
have been allocated by the caller using \fBTcl_Alloc\fR or \fBckalloc\fR.
.AP Tcl_QueuePosition position in
Where to add the new event in the queue:  \fBTCL_QUEUE_TAIL\fR,
\fBTCL_QUEUE_HEAD\fR, or \fBTCL_QUEUE_MARK\fR.
.AP int flags in
What types of events to service.  These flags are the same as those
passed to \fBTcl_DoOneEvent\fR.
.AP Tcl_EventDeleteProc *deleteProc in
Procedure to invoke for each queued event in \fBTcl_DeleteEvents\fR.
.VS
.AP int mode in
Inidicates whether events should be serviced by \fBTcl_ServiceAll\fR.
Must be one of \fBTCL_SERVICE_NONE\fR or \fBTCL_SERVICE_ALL\fR.
.VE
.BE

.SH INTRODUCTION
.PP
.VS
The interfaces described here are used to customize the Tcl event
loop.  The two most common customizations are to add new sources of
events and to merge Tcl's event loop with some other event loop, such
as one provided by an application in which Tcl is embedded.  Each of
these tasks is described in a separate section below.
.VE
.PP
The procedures in this manual entry are the building blocks out of which
the Tcl event notifier is constructed.  The event notifier is the lowest
layer in the Tcl event mechanism.  It consists of three things:
.IP [1]
Event sources: these represent the ways in which events can be
generated.  For example, there is a timer event source that implements
the \fBTcl_CreateTimerHandler\fR procedure and the \fBafter\fR
command, and there is a file event source that implements the
\fBTcl_CreateFileHandler\fR procedure on Unix systems.  An event
source must work with the notifier to detect events at the right
times, record them on the event queue, and eventually notify
higher-level software that they have occurred.  The procedures
\fBTcl_CreateEventSource\fR, \fBTcl_DeleteEventSource\fR,
and \fBTcl_SetMaxBlockTime\fR, \fBTcl_QueueEvent\fR, and
\fBTcl_DeleteEvents\fR are used primarily by event sources.
.IP [2]
The event queue: there is a single queue for the whole application,
containing events that have been detected but not yet serviced.  Event
sources place events onto the queue so that they may be processed in
order at appropriate times during the event loop. The event queue
guarantees a fair discipline of event handling, so that no event
source can starve the others.  It also allows events to be saved for
servicing at a future time.
.VS
\fBTcl_QueueEvent\fR is used (primarily
by event sources) to add events to the event queue and 
\fBTcl_DeleteEvents\fR is used to remove events from the queue without
processing them.
.IP [3]
The event loop: in order to detect and process events, the application
enters a loop that waits for events to occur, places them on the event
queue, and then processes them.  Most applications will do this by
calling the procedure \fBTcl_DoOneEvent\fR, which is described in a
separate manual entry.
.PP
Most Tcl applications need not worry about any of the internals of
the Tcl notifier.  However, the notifier now has enough flexibility
to be retargeted either for a new platform or to use an external event
loop (such as the Motif event loop, when Tcl is embedded in a Motif
application).  The procedures \fBTcl_WaitForEvent\fR and
\fBTcl_SetTimer\fR are normally implemented by Tcl, but may be
replaced with new versions to retarget the notifier (the \fBTcl_Sleep\fR,
\fBTcl_CreateFileHandler\fR, and \fBTcl_DeleteFileHandler\fR must
also be replaced; see CREATING A NEW NOTIFIER below for details).
The procedures \fBTcl_ServiceAll\fR, \fBTcl_ServiceEvent\fR,
\fBTcl_GetServiceMode\fR, and \fBTcl_SetServiceMode\fR are provided
to help connect Tcl's event loop to an external event loop such as
Motif's.
.SH "NOTIFIER BASICS"
.VE
.PP
The easiest way to understand how the notifier works is to consider
what happens when \fBTcl_DoOneEvent\fR is called.
\fBTcl_DoOneEvent\fR is passed a \fIflags\fR argument that indicates
what sort of events it is OK to process and also whether or not to
block if no events are ready.  \fBTcl_DoOneEvent\fR does the following
things:
.IP [1]
Check the event queue to see if it contains any events that can
be serviced.  If so, service the first possible event, remove it
.VS
from the queue, and return.  It does this by calling
\fBTcl_ServiceEvent\fR and passing in the \fIflags\fR argument.
.VE
.IP [2]
Prepare to block for an event.  To do this, \fBTcl_DoOneEvent\fR
invokes a \fIsetup procedure\fR in each event source.
The event source will perform event-source specific initialization and
.VS
possibly call \fBTcl_SetMaxBlockTime\fR to limit how long
.VE
\fBTcl_WaitForEvent\fR will block if no new events occur.
.IP [3]
Call \fBTcl_WaitForEvent\fR.  This procedure is implemented differently
on different platforms;  it waits for an event to occur, based on the
information provided by the event sources.
It may cause the application to block if \fItimePtr\fR specifies
an interval other than 0.
\fBTcl_WaitForEvent\fR returns when something has happened,
such as a file becoming readable or the interval given by \fItimePtr\fR
expiring.  If there are no events for \fBTcl_WaitForEvent\fR to
wait for, so that it would block forever, then it returns immediately
and \fBTcl_DoOneEvent\fR returns 0.
.IP [4]
Call a \fIcheck procedure\fR in each event source.  The check
procedure determines whether any events of interest to this source
occurred.  If so, the events are added to the event queue.
.IP [5]
Check the event queue to see if it contains any events that can
be serviced.  If so, service the first possible event, remove it
from the queue, and return.
.IP [6]
See if there are idle callbacks pending. If so, invoke all of them and
return.
.IP [7]
Either return 0 to indicate that no events were ready, or go back to
step [2] if blocking was requested by the caller.

.SH "CREATING A NEW EVENT SOURCE"
.PP
An event source consists of three procedures invoked by the notifier,
plus additional C procedures that are invoked by higher-level code
to arrange for event-driven callbacks.  The three procedures called
by the notifier consist of the setup and check procedures described
above, plus an additional procedure that is invoked when an event
is removed from the event queue for servicing.
.PP
The procedure \fBTcl_CreateEventSource\fR creates a new event source.
Its arguments specify the setup procedure and check procedure for
the event source.
\fISetupProc\fR should match the following prototype:
.CS
typedef void Tcl_EventSetupProc(
	ClientData \fIclientData\fR,
	int \fIflags\fR);
.CE
The \fIclientData\fR argument will be the same as the \fIclientData\fR
argument to \fBTcl_CreateEventSource\fR;  it is typically used to
point to private information managed by the event source.
The \fIflags\fR argument will be the same as the \fIflags\fR
argument passed to \fBTcl_DoOneEvent\fR except that it will never
be 0 (\fBTcl_DoOneEvent\fR replaces 0 with \fBTCL_ALL_EVENTS\fR).
\fIFlags\fR indicates what kinds of events should be considered;
if the bit corresponding to this event source isn't set, the event
source should return immediately without doing anything.  For
example, the file event source checks for the \fBTCL_FILE_EVENTS\fR
bit.
.PP
\fISetupProc\fR's job is to make sure that the application wakes up
when events of the desired type occur.  This is typically done in a
platform-dependent fashion.  For example, under Unix an event source
might call \fBTcl_CreateFileHandler\fR; under Windows it might
request notification with a Windows event.  For timer-driven event
sources such as timer events or any polled event, the event source
can call \fBTcl_SetMaxBlockTime\fR to force the application to wake
up after a specified time even if no events have occurred.
.VS
If no event source calls \fBTcl_SetMaxBlockTime\fR
then \fBTcl_WaitForEvent\fR will wait as long as necessary for an
event to occur; otherwise, it will only wait as long as the shortest
interval passed to \fBTcl_SetMaxBlockTime\fR by one of the event
sources.  If an event source knows that it already has events ready to
report, it can request a zero maximum block time.  For example, the
setup procedure for the X event source looks to see if there are
events already queued.  If there are, it calls
\fBTcl_SetMaxBlockTime\fR with a 0 block time so that
\fBTcl_WaitForEvent\fR does not block if there is no new data on the X
connection.
.VE
The \fItimePtr\fR argument to \fBTcl_WaitForEvent\fR points to
a structure that describes a time interval in seconds and
microseconds:
.CS
typedef struct Tcl_Time {
	long \fIsec\fR;
	long \fIusec\fR;
} Tcl_Time;
.CE
The \fIusec\fR field should be less than 1000000.
.PP
.VS
Information provided to \fBTcl_SetMaxBlockTime\fR
is only used for the next call to \fBTcl_WaitForEvent\fR; it is
discarded after \fBTcl_WaitForEvent\fR returns.
.VE
The next time an event wait is done each of the event sources'
setup procedures will be called again, and they can specify new
information for that event wait.
.PP
.VS
If the application uses an external event loop rather than
\fBTcl_DoOneEvent\fR, the event sources may need to call
\fBTcl_SetMaxBlockTime\fR at other times.  For example, if a new event
handler is registered that needs to poll for events, the event source
may call \fBTcl_SetMaxBlockTime\fR to set the block time to zero to