RPC over DDS – Presentation by Gerardo Pardo-Castellote, CTO, RTI

1. DDS
RPC
over
DDS
Gerardo
Pardo-­‐Castellote,
Ph.D.
Chief
Technology
Officer,
RTI
Sumant
Tambe,
Ph.D.
Senior
SoBware
Reseach
Engineer,
RTI
October
2014

2. ©
2014
Real-­‐Time
InnovaJons,
Inc.
Outline
• Goals
• Background
• Status
• Details
• More
info

3. ©
2014
Real-­‐Time
InnovaJons,
Inc.
Goals
• Provide
standard
and
interoperable
way
means
to
support
“RPC”
communicaJon
paQerns
in
DDS
• Support
the
PaQers:
– Request/Reply
– Service
InvocaJon
– Remote
Procedure
Call
– Remote
Method
InvocaJon
• Support
invocaJon
of
IDL-­‐specified
interfaces
over
DDS
– Provide
a
simpler
way
to
migrate
CORBA
applicaJons
to
DDS
– Support
familiar
“remote
interface”
programming
style
equivalent
to
Java
RMI
and
Apache
ThriB

4. Advantages
of
RPC
over
DDS
• Client
and
Servers
are
decoupled
©
2014
Real-­‐Time
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Inc.
– No
startup
dependencies
• QoS
enforcement
to
support
service
SLAs
– Ownership–Redundant
pool
of
servers
– Lifespan–request
is
only
valid
for
the
next
N
sec
– Durability-­‐request/replies
will
be
eventually
received
and
processed
– CancellaJon–
aBer
a
good
quality
response
has
arrived
• Data-­‐Centricity
– Explicit
trace-­‐ability
– InteracJon
state
can
be
Monitored,
Logged,
Audited,
Stored,
Manipulated
• Watch
by
subscribing
to
requests
and/or
responses
(wire-­‐tap)
• One
middleware
–
leverage
DDS
infrastructure
– Suited
for
real-­‐Jme
systems
– MulJpla`orm,
MulJlanguage,
Interoperable

5. But
I
can
already
do
it...
True:
• I
can
write
my
own
RCP
using
request/reply
Topics
©
2014
Real-­‐Time
InnovaJons,
Inc.
• RTI
Connext
already
supports
a
“Request/Reply”
equivalent
to
RPC
• Some
other
vendors
do
similar
things
But…
• The
mapping
from
service
to
Topics
and
Types
is
ad-­‐
hoc.
• These
approaches
are
not
portable/Interoperable
• Gebng
everything
right
is
cumbersome
at
best

6. How
can
I
do
it
myself?
• Map
Interfaces
to
types
&
Topics…
©
2014
Real-­‐Time
InnovaJons,
Inc.
– One
Topic
per
interface,
one
per
operaJon?
– What
are
the
types.
How
to
map
excepJons,
output
parameters,
…
– What
happens
if
the
interfaces
change,
e.g.
operaJon
is
added
or
moved?
• Implement
necessary
plumbing:
• Setup
request
topic
and
type
• Setup
reply
topic
and
type
• Filter
unwanted
requests
• Filter
unwanted
replies

7. But
RPC
is
not
a
good/robust
idea/
design
paQern….
• RPC
versus
Desired
State
PaQern
Goal
State
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2014
Real-­‐Time
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Inc.
– Insight:
OBen
a
request-­‐reply
can
be
modeled
as
stateful
data-­‐centric
interacJons
write
Current
State
Affect
Service
Client
Service
Provider
Desired
State
read
write
read
read

8. RPC
vs
Desired
State
• Desired
state
is
good
&
more
robust
if
the
“request”
©
2014
Real-­‐Time
InnovaJons,
Inc.
actually
represents:
– a
request
to
change
of
system
state
– Take
a
long
Jme
to
fulfill
– Needs
to
be
observable
by
others
• However:
– Many
requests
that
do
not
represent
changes
to
state:
Database
Query,
Read
a
File…
– People
familiar
for
“Service”
or
“Request/Reply”
paQern
may
find
Directed
State
cumbersome
–specially
if
extra
robustness
is
unwarranted
RPC
over
DDS
provides
best
of
both
worlds!

9. Example:
RobotControl
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2014
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Inc.
module robot {
@DDSService
interface RobotControl
{
void command(Command command);
float setSpeed(float speed) raises (TooFast);
float getSpeed();
void getStatus(out Status status);
};
}

10. RobotControl
Client
©
2014
Real-­‐Time
InnovaJons,
Inc.
import org.omg.dds.rpc.*;
public class TestRobot {
static void createRobotClient() {
RPCRuntime runtime = RPCRuntime.getInstance(TestRobot.class.getClassLoader());
ClientParams clientParams = runtime.createClientParams(); // optional
RobotControlSupport.Client robotClient =
RobotControlSupport.createClient(
clientParams.withServiceName(”TestRobot”)
.withInstanceName(“iRobot”)); // more configs available
robotClient.waitForService(); // optional
robotClient.getSpeed();
}
}

11. RobotControl
Service
(Java)
package robot;
import robot.RobotControl;
public class MyRobot implements RobotControl
{
public void command(Command command) { }
public float setSpeed(float speed) { return 1; }
public float getSpeed() { return 2; }
public void getStatus(/* out */ Status status) { }
©
2014
Real-­‐Time
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Inc.
}
import org.omg.dds.rpc.*;
public class TestRobot {
public static void createRobotServer()
{
RPCRuntime runtime = RPCRuntime.getInstance(TestRobot.class.getClassLoader());
MyRobot myRobot = new MyRobot();
Server server = runtime.createServer(); // Configurable using ServerParams
RobotControlSupport.Service service =
RobotControlSupport.createService(myRobot, server); // Configurable using ServiceParams
server.run(); // blocking
}
}

12. RobotControl
Requester
public class TestRobot {
static void createRobotRequester() {
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2014
Real-­‐Time
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Inc.
RPCRuntime runtime =
RPCRuntime.getInstance(TestRobot.class.getClassLoader());
RequesterParams reqParams = runtime.createRequesterParams();
// change params here if you like
Requester<RobotControlSupport.RequestType,
RobotControlSupport.ReplyType>
requester = runtime.createRequester(
RobotControlSupport.RequestType.class,
RobotControlSupport.ReplyType.class,
reqParams);
RobotControlSupport.RequestType request =
new RobotControlSupport.RequestType();
// populate request
requester.sendRequest(request);
}
}

13. RobotControl
Replier
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2014
Real-­‐Time
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Inc.
public class TestRobot {
static void createRobotReplier() {
RPCRuntime runtime =
RPCRuntime.getInstance(TestRobot.class.getClassLoader());
ReplierParams repParams = runtime.createReplierParams();
// change params here if you like
Replier<RobotControlSupport.RequestType,
RobotControlSupport.ReplyType>
replier = runtime.createReplier(
RobotControlSupport.RequestType.class,
RobotControlSupport.ReplyType.class,
repParams);
Sample<RobotControlSupport.RequestType>
request = replier.receiveRequest();
}
}

14. RobotControlSupport
public abstract class RobotControlSupport {
public final static class RequestType {
// omg.dds.rpc.RequestHeader header;
// robot.RobotControl_Call data;
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2014
Real-­‐Time
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Inc.
}
public final static class ReplyType {
// omg.dds.rpc.ReplyHeader header;
// robot.RobotControl_Return data
}
public interface Client
extends RobotControl,
RobotControlAsync,
ClientEndpoint
{
}
public interface Service extends ServiceEndpoint
{
}
public static final RobotControlSupport.Client createClient();
public static final RobotControlSupport.Service createService(RobotControl impl);
// more client and service factory methods here
}

15. What
needs
to
be
specified
• Mapping
to
DDS
Topics
&
Filters
©
2014
Real-­‐Time
InnovaJons,
Inc.
– Each
operaJon
maps
to
a
pair
of
topics?
• Simplicity,
Flexibility
vs
Scalability
– Each
interface
to
a
pair
of
Topics?
• What
are
the
types?
Inheritance?
– Is
publish-­‐subscribe
allowed?
e.g.
audiJng,
monitoring…
• Mapping
to
DDS
Data-­‐types
– How
to
model
operaJons?
Parameters
(in,
our)
return,
excepJons,
…
– Fragility
upon
interfaces
/
operaJons
changes?
– Describable
using
X-­‐TYPES?
• DDS
API
and
DDS-­‐RTPS
impact
– Are
extensions
required?
– Deployment
on
top
of
exisJng
DDS
• Language
Bindings
(C,
C++,
Java,
C#,
…)

16. Client Application Service
©
2014
Real-­‐Time
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Inc.
Architecture
Service
Implementa8on
Lang.
Bind.
GUID2
Data
Writer
Client-­‐side
Invoker
Data
Reader
Data
Reader
Data
Writer
GUID1
SN1
Foo
GUID2
SN2
GUID1
SN1
Bar
Message-id1
Message-id2
Correlation-id1
Language
Binding
Bar
Svc.method(in
Foo);
Content-­‐based
Filter
for
filtering
unwanted
replies
Foo
Bar
GUID1
Invoke
Return
Call Topic
Return Topic
Foo
Bar

17. Basic
and
Enhanced
Service
Mappings
• Basic
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2014
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Inc.
– Highest
portability
– Enables
RPC
on
top
of
exisJng
(v1.3
or
earlier)
DDS
ImplementaJons
• Enhanced
– Elegant,
Clean
– Leverages
DDS-­‐XTypes
for
type
matching,
– Adds
support
for
Robust
service
discovery,
Implicit
request/reply
correlaJon
Mapping
Aspect Basic
Service
Mapping
Profile Enhanced
Service
Mapping
Profile
Correla8on
Informa8on
(request-­‐id)
Explicitly
added
to
the
data-­‐type Implicit.
They
appear
on
the
Sample
meta-­‐data.
Topic
Mapping One
request
topic
and
one
reply
topic
per
interface.
2*N
for
a
hierarchy
of
N
interfaces.
One
request
and
one
reply
topic
per
interface.
Independent
of
interface
hierarchy.
Type
Mapping Synthesized
types
compaJble
with
l e g a c y
( p r e
D D S -­‐ X T y p e s )
implementaJons.
Use
faciliJes
of
DDS-­‐XTypes
for
type
descripJons,
annotaJons,
and
type-­‐
compaJbility
checks.
Discovery No
special
extensions.
Robust
service
discovery
(no
sample
loss
due
to
transient
states)

18. Language
Bindings
• Two
©
2014
Real-­‐Time
InnovaJons,
Inc.
types
of
language
bindings
– High-­‐level
binding
that
provide
func%on-­‐call
semanJcs
– Low-­‐level
binding
that
are
akin
to
send/receive
(but
sJll
higher
level
than
raw
DDS
read/take/write)
• Strong
separaJon
between
the
data
model
and
language
binding
Client
ApplicaJon
FuncJon-­‐call
language
binding
DDS
API
Service
Specification
(IDL)
Client
ApplicaJon
Request-­‐Reply
language
binding
DDS
API
Service
ImplementaJon
FuncJon
call
language
binding
DDS
API
Service
ImplementaJon
Request-­‐Reply
language
binding
DDS
API
Service-­‐specific
Interoperable/Evolvable
Data
model
(DDS/RTPS)

19. ©
2014
Real-­‐Time
InnovaJons,
Inc.
QoS
Mapping
• Default
strict
reliable
(request
and
reply)
– RELIABLE
reliability
– KEEP_ALL
history
– VOLATILE
durability
• Can
be
changed
by
the
user
on
a
per-­‐service
level

20. ©
2014
Real-­‐Time
InnovaJons,
Inc.
@DDSService
interface RobotControl
{
struct
RobotControl_setSpeed_In
{
long
s;
};
struct
RobotControl_getSpeed_In
{
boolean
return_;
};
float setSpeed(float speed) raises (TooFast);
float getSpeed();
void start();
void stop();
};
@choice
@autoid
struct
RobotControl_Request
{
RobotControl_setSpeed_In
setSpeed;
RobotControl_getSpeed_In
getSpeed;
RobotControl_start_In
start;
RobotControl_stop_In
stop;
@empty
};
struct
start_In
{
octet
dummy_;};
@empty
struct
stop_In
{
octet
dummy_;};

21. float setSpeed(float speed) raises (TooFast);
float getSpeed();
void start();
void stop();
©
2014
Real-­‐Time
InnovaJons,
Inc.
@DDSService
interface RobotControl
{
};
struct
RobotControl_setSpeed_Out
{
float
return_;
//
Also
inout
and
out
params
};
…
@choice
@autoid
struct
RobotControl_setSpeed_Result
{
RobotControl_setSpeed_Out
out;
SystemExcepJonCode
sysx_;
TooFast
toofast_ex;
};
…
@choice
@autoid
struct
RobotControl_Reply
{
RobotControl_setSpeed_Result
setSpeed;
RobotControl_getSpeed_Result
getSpeed;
RobotControl_start_Result
start;
RobotControl_stop_Result
stop;
};

22. ©
2014
Real-­‐Time
InnovaJons,
Inc.
Status
• Ongoing
standard
at
OMG
• RFP
was
issued
in
June
2012
• IniJally
2
compeJng
submissions:
1. Joint
RTI
+
eProsima
(later
joined
by
TwinOaks)
2. PrismTech
• Very
different
approaches
–
not
converging
– EvaluaJon
team
represenJng
5
companies
formed
to
provide
feedback
• RecommendaJon
was
to
simplify
RTI/eProsima
submission
• PrismTech
dropped
their
submission
and
joined
RTI/eProsimas’/TwinOaks
• Expected
to
be
voted
and
adopted
in
Dec
2014
• Completed
FuncJon-­‐Call
and
Request/Reply
language
binding
– Java
(hQps://github.com/rJcommunity/dds-­‐rpc-­‐java)
– C++*
(hQps://github.com/rJcommunity/dds-­‐rpc-­‐cxx)
– eProsima
has
POC
implementaJon
of
“basic”
profile
working
with
several
DDS
implementaJons

23. QuesJons?
©
2014
Real-­‐Time
InnovaJons,
Inc.

24. ©
2014
Real-­‐Time
InnovaJons,
Inc.
Find
out
more…
dds.omg.org
www.omg.org
www.rJ.com
community.rJ.com
demo.rJ.com
www.youtube.com/realJmeinnovaJons
blogs.rJ.com
www.twiQer.com/RealTimeInnov
www.facebook.com/RTIsoBware
www.slideshare.net/GerardoPardo
www.slideshare.net/RealTimeInnovaJons