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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
<html>
<head>
<title>Real-time Event Channel Configuration</title>
<!-- $Id$ -->
</head>
<body>
<CENTER>
<h1>Real-time Event Channel Configuration</h1>
</CENTER>
<H3>Configuring the Event Channel at Compilation Time</H3>
<P>TAO's Real-Time Event Channel can be configured at compilation
time to use a different payload than its default. To do so
there are several options:
</P>
<UL>
<LI><P>To eliminate the <CODE>CORBA::Any</CODE> field in the
event payload you should define the
<CODE>TAO_LACKS_EVENT_CHANNEL_ANY</CODE>
macro when invoking the IDL compiler.
You can do as follows:
<PRE>
$ cd $TAO_ROOT/orbsvcs/orbsvcs
$ make TAO_IDLFLAGS=-DTAO_LACKS_EVENT_CHANNEL_ANY
</PRE>
</P>
</LI>
<LI><P>Similarly you can eliminate the octet sequence field in
the event payload using:
<PRE>
$ cd $TAO_ROOT/orbsvcs/orbsvcs
$ make TAO_IDLFLAGS=-DTAO_LACKS_EVENT_CHANNEL_OCTET_SEQUENCE
</PRE>
</P>
</LI>
<LI><P>Finally you can provide your own event payload, to do
this you should Replace the contents of the
<CODE>RtecDefaultEventData.idl</CODE>
and define some IDL structure named
<CODE>RtecEventData</CODE>.
For example, you could define you own event type as follows:
<PRE>
// Replace RtecDefaultEventData.idl with this:
struct RtecEventData
{
sequence<long> my_event_payload;
};
</PRE>
</LI>
</UL>
<H3>Run-time Configuration</H3>
<P>The new implementation of the real-time event channel uses a
factory to build all the objects and strategies it requires.
The factory can be dynamically loaded using ACE Service
Configurator, this is extremely convenient because the factory
can also parse options in the Service Configurator script file.
</P>
<P>The current implementation provides a default implementation
for this Factory, this document describes the options used by
this default implementation.
</P>
<H3>The configuration file</H3>
<P>The real-time event channel uses the same service configurator
file that the ORB uses, the default name for this file is
<CODE>svc.conf</CODE>, but the ORB option
<CODE>-ORBSvcConf</CODE> can be used to override this.
The format of the file is described in detail in
the service configurator documentation, but the relevant section
for the event channel looks like this:
</P>
<PRE>
# Comments go here...
# More comments if you want to...
static EC_Factory "-ECFiltering basic ....."
</PRE>
<P>All the event service factory options start with
<CODE>-EC</CODE></P>
<H3>The options</H3>
<P><TABLE BORDER="2" CELLSPACING="2" CELLPADDING="0">
<TR>
<TH>Option</TH>
<TH>Description</TH>
</TR>
<!-- <TR NAME="ECDispatching"> -->
<TR>
<TD><CODE>-ECDispatching</CODE>
<EM>dispatching_strategy</EM>
</TD>
<TD>Select the dispatching strategy used by the real-time
event service. A <EM>reactive</EM> strategy will use the
same thread that received the event from the supplier to
push the event to all the consumers,
the <EM>priority</EM> strategy will use a prioritized pool
of threads and will query the scheduling service to select
the thread that will dispatch each event;
the <EM>mt</EM> strategy will also use a pool of threads,
but the thread to dispatch is randomly selected.
</TD>
</TR>
<!-- <TR NAME="ECDispatchingThreads"> -->
<TR>
<TD><CODE>-ECDispatchingThreads</CODE>
<EM>number_of_threads</EM>
</TD>
<TD>Select the number of threads used bythe <EM>mt</EM>
dispatching strategy.
</TD>
</TR>
<!-- <TR NAME="ECFiltering"> -->
<TR>
<TD><CODE>-ECFiltering</CODE>
<EM>consumer_filtering_strategy</EM>
</TD>
<TD>Select the filtering strategy used by the consumers.
The <EM>null</EM> filtering strategy will build trivial
filters for all consumers.
The <EM>basic</EM> filtering strategy supports
disjunction, conjunctions and timeouts based on the
subscriptions passed by the consumer during the connect
call.
The <EM>priority</EM> filtering strategy supports the same
features, but it also collaborates with the scheduling
service to build the dependency graph.
</TD>
</TR>
<!-- <TR NAME="ECSupplierFiltering"> -->
<TR>
<TD><CODE>-ECSupplierFiltering</CODE>
<EM>supplier_filtering_strategy</EM>
</TD>
<TD>The event channel can also perform some filtering close
to the suppliers by minimizing the number of consumers
that are tested for given event.
If the strategy is <EM>null</EM> then a global collection
of consumers is maintained and each event is filtered by
each consumer.
If the strategy is <EM>per-supplier</EM> then the EC uses
the supplier publications and the consumer subscriptions
to determine which consumers could potentially be
interested in events for each supplier.
This set of consumers is usually smaller than the complete
set and it is thus faster to traverse it, but keeping more
collections of consumers increases the connection and
disconnection time as well as the memory requirements.
</TD>
</TR>
<!-- <TR NAME="ECTimeout"> -->
<TR>
<TD><CODE>-ECTimeout</CODE>
<EM>timeout_strategy</EM>
</TD>
<TD>A consumer can request that the event channel generate
periodic or oneshot timeout events.
This option controls the strategy to generate the
timeouts,
using <EM>reactive</EM> the same reactor used for the ORB
is used by the event service.
The <EM>priority</EM> strategy uses a prioritized group of
threads, timeouts with higher rate are generated by
threads of higher priority.
<BR><B>NOTE: The <EM>priority</EM> strategy is not
implemented</B>
</TD>
</TR>
<!-- <TR NAME="ECObserver"> -->
<TR>
<TD><CODE>-ECObserver</CODE>
<EM>observer</EM>
</TD>
<TD>The event channel uses the Observer pattern to report
changes in the subscriptions and publications of its
suppliers and consumers; this is specially useful in the
implementation of event channel gateways.
The user can disable this feature by selecting the
<EM>null</EM> strategy;
whereas the <EM>basic</EM> strategy provides a simple, yet
efficient implementation.
</TD>
</TR>
<!-- <TR NAME="ECScheduling"> -->
<TR>
<TD><CODE>-ECScheduling</CODE>
<EM>scheduling_strategy</EM>
</TD>
<TD>The event channel can collaborate with the scheduling
service to build the dependency list between the consumers
and the suppliers.
If the <EM>null</EM> scheduling strategy is selected this
feature is disabled,
the <EM>priority</EM> strategy enables this feature.
<BR><B>NOTE:<B> The default is to have the feature disabled.
</TD>
</TR>
<!-- <TR NAME="ECProxyConsumerLock"> -->
<TR>
<TD><CODE>-ECProxyConsumerLock</CODE>
<EM>lock_type</EM>
</TD>
<TD>Select the lock type (<EM>null</EM>, <EM>thread</EM> or
<EM>recursive</EM>) to synchronize access to the
ProxyPushConsumer state.
</TD>
</TR>
<!-- <TR NAME="ECProxySupplierLock"> -->
<TR>
<TD><CODE>-ECProxySupplierLock</CODE>
<EM>lock_type</EM>
</TD>
<TD>Select the lock type (<EM>null</EM>, <EM>thread</EM> or
<EM>recursive</EM>) to synchronize access to the
ProxyPushSupplier state.
</TD>
</TR>
<!-- <TR NAME="ECORBId"> -->
<TR>
<TD><CODE>-ECORBId</CODE>
<EM>orbid</EM>
</TD>
<TD>Set the name of the ORB used by the event service, only
useful in applications that create multiple ORBs and
activate the event service in one of them.
</TD>
</TR>
<!-- <TR NAME="ECConsumerControl"> -->
<TR>
<TD><CODE>-ECConsumerControl</CODE>
<EM>policy</EM>
</TD>
<TD>Select the consumer control policy (<EM>null</EM> or
<EM>reactive</EM>) to detect and discard broken consumer
proxies.
</TD>
</TR>
<!-- <TR NAME="ECSupplierControl"> -->
<TR>
<TD><CODE>-ECSupplierControl</CODE>
<EM>policy</EM>
</TD>
<TD>Select the supplier control policy (<EM>null</EM> or
<EM>reactive</EM>) to detect and discard broken supplier
proxies.
</TD>
</TR>
<!-- <TR NAME="ECConsumerPeriod"> -->
<TR>
<TD><CODE>-ECConsumerPeriod</CODE>
<EM>period</EM>
</TD>
<TD>Set the period (in microseconds) used by the reactive
consumer control policy to poll the state of the
consumer proxies.
</TD>
</TR>
<!-- <TR NAME="ECSupplierPeriod"> -->
<TR>
<TD><CODE>-ECSupplierPeriod</CODE>
<EM>period</EM>
</TD>
<TD>Set the period (in microseconds) used by the reactive
supplier control policy to poll the state of the
supplier proxies.
</TD>
</TR>
<!-- <TR NAME="ECProxyPushConsumerCollection"> -->
<TR>
<TD><CODE>-ECProxyPushConsumerCollection</CODE>
<EM>flag[:flags]</EM>
</TD>
<TD><P>Configure the data structure and strategies used to
implement collections of
<CODE>ProxyPushConsumers</CODE>.
The argument is a colon separated list of flags, with
the following semantics:
<TABLE>
<TR><TH>Flag</TH><TH>Description</TH><
</TR>
<TR>
<TD>MT</TD>
<TD>Use regular mutexes and/or condition
variables for serialization.
</TD>
<TD>ST</TD>
<TD>Use null mutexes and/or condition
variables for serialization.
</TD>
<TD>LIST</TD>
<TD>Implement the collection using an ordered list,
fast for iteration (i.e. during event dispatching),
but slow for insertion and removal (i.e. when
clients connect and disconnect from the EC).
</TD>
<TD>RB_TREE</TD>
<TD>Implement the collection using a Red-Black tree,
slow for iteration (i.e. during event dispatching),
but fast for insertion and removal (i.e. when
clients connect and disconnect from the EC).
</TD>
<TD>IMMEDIATE</TD>
<TD>Threads block until they can execute a change on
the data structure, the system must use other
approaches to guarantee that the iterators are not
invalidated during event dispatching. For example,
use a separate dispatching thread.
</TD>
<TD>COPY_ON_READ</TD>
<TD>Before initiating an iteration to dispatch events
(or similar tasks) a copy of the complete collection
is performed.
This solves most of the synchronization problems,
but introduces a significant source of overhead and
priority inversions on the critical path.
</TD>
<TD>COPY_ON_WRITE <STRONG>UNIMPLEMENTED</STRONG></TD>
<TD>Similar to the previous one, but the copy is only
performed when needed.
</TD>
<TD>DELAYED</TD>
<TD>Threads that need to change the collection can
detect if that change will invalidate iterators used
by other threads.
If so, the thread posts the change on a queue that
is executed once the collection is no longer in
use.
</TD>
</TR>
</TABLE>
</P>
</TD>
</TR>
<!-- <TR NAME="ECPushSupplierSet"> -->
<TR>
<TD><CODE>-ECPushSupplierSet</CODE>
</TD>
<TD><P>Obsolete option, ignored.
</P>
</TD>
</TR>
<!-- <TR NAME="ECConsumerAdminLock"> -->
<TR>
<TD><CODE>-ECConsumerAdminLock</CODE>
</TD>
<TD>Obsolete option, ignored in the current version.
</TD>
</TR>
<!-- <TR NAME="ECSupplierAdminLock"> -->
<TR>
<TD><CODE>-ECSupplierAdminLock</CODE>
</TD>
<TD>Obsolete option, ignored in the current version.
</TD>
</TR>
</TABLE>
</P>
<H3>The constructor</H3>
<P>The <CODE>TAO_EC_Event_Channel</CODE> class implements the
<CODE>RtecEventChannelAdmin::EventChannel</CODE> interface;
this class takes one mandatory and two optional parameters in
its constructor:
</P>
<PRE>
TAO_EC_Event_Channel (const TAO_EC_Event_Channel_Attributes& attributes,
TAO_EC_Factory* factory = 0,
int own_factory = 0);
</PRE>
<P>The <CODE>factory</CODE> is an optional parameter to override
the default strategy factory used by the event channel,
the event channel will destroy the factory if the
<CODE>own_factory</CODE> argument is true.
</P>
<P>The <CODE>attributes</CODE> parameter can be used to fine tune
some of the algorithms and strategies used by the event channel,
the default values are probably OK for most applications.
Notice that the attributes include the POA used to activate the
ConsumerAdmin, SupplierAdmin, ProxyPushConsumer and
ProxyPushSupplier objects;
this POAs must have the <CODE>IMPLICIT_ACTIVATION</CODE> and the
<CODE>SYSTEM_ID</CODE> policies (as the RootPOA does).
</P>
<P><TABLE BORDER="2" CELLSPACING="2" CELLPADDING="0">
<TR><TH>Attribute</TH><TH>Description</TH></TR>
<TR><TD><CODE>consumer_reconnect</CODE></TD>
<TD>If the attribute is not zero then the same consumer can
call <CODE>connect_push_consumer</CODE> on its
ProxyPushSupplier multiple times to change its
subscriptions;
this is usually more efficient that disconnecting and
connecting again.
</TD>
</TR>
<TR><TD><CODE>supplier_reconnect</CODE></TD>
<TD>If the attribute is not zero then the same supplier can
call <CODE>connect_push_supplier</CODE> on its
ProxyPushConsumer multiple times to change its
publications;
this is usually more efficient that disconnecting and
connecting again.
</TD>
</TR>
<TR><TD><CODE>busy_hwm</CODE></TD>
<TD>When using the delayed strategy to update
ProxyPushSupplier sets this flag controls the maximum
number of thread that can simultaneously iterate over the
set before blocking.
It can be used to avoid starvation in delayed updates on
the set.
</TD>
</TR>
<TR><TD><CODE>max_write_delay</CODE></TD>
<TD>When using the delayed strategy to update
ProxyPushSupplier sets this flag controls the maximum
number of threads that will initiate dispatching
<B>after</B> a change has been posted.
Any thread after that is blocked until the operations are
performed.
It can be used to completely stop starvation of delayed
updates on the set.
</TD>
</TR>
<TR><TD><CODE>scheduler</CODE></TD>
<TD>Most configurations of the real-time event channel do
not require an scheduler.
If any of the strategies that require an scheduling
service is selected then this attribute should be set
appropiately.
</TD>
</TR>
</TABLE>
</P>
<P><HR><P>
Back to the TAO <A HREF="index.html">components documentation</A>.
<!--#include virtual="/~schmidt/cgi-sig.html" -->
<address><a href="mailto:coryan@cs.wustl.edu">Carlos O'Ryan</a></address>
<!-- Created: Thu Jul 1 21:44:28 CDT 1999 -->
<!-- hhmts start -->
Last modified: Tue Feb 1 13:50:47 PST 2000
<!-- hhmts end -->
</body>
</html>
|
