1. No Heap Remote Objects for Distributed
Real-Time Java
Pablo Basanta-Val, Marisol García-Valls,
and Iria Estévez-Ayres
mailto:pbasanta@it.uc3m.es
†Jornadas de Tiempo Real 2011- Madrid( )
Publicado en ACM Transactions On Embedded Systems

2. Outline
• Context and Motivation
• No-Heap Remote Objects
– Basic Model
• Programming model
• Example
• Performance
– Extended Model
• Programming patterns
• Extended model
• Performance
• Conclusion and ongoing work
2

3. Memory management for real-
time Java
• Techniques used for memory management in real-time Java
(RTSJ)
– Auto-managed memory (object pools)
– Garbage collection (and its RT* variants)
– Regions (ScopedMemory)
• Memory management issues in distributed real-time Java
(DRTSJ)
– Real-time garbage collection
– Distributed Garbage Collection
– Regions
• Current garbage collectors may be not enough for
distributed real-time applications
– E.g. a heap with 1Gb may introduce a 30 seconds delay
JRT-11 3

4. State of the art
Denomination Technologies Goals
RT- CORBA+ Implementation of RT-CORBA with RTSJ
RTZen
RTSJ
DRTSJ RMI+RTSJ A specification for distributed real-time Java
RT-RMI-York RMI+RTSJ A framework for distributed real-time Java.
RT-RMI-UPM RMI+RTSJ Profiles for distributed real-time Java
DRTJava-on-CSP CSP+Java Produce an alternative based on CSP formalisms
RTJ-COM RTSJ A component framework for embedded Java
Scratchpad RTSJ A no-heap component model for real-time Java
A distributed real-time object-oriented platform
APICOM RTSJ +CAN
• There is not a simple technique to remove the GC’s from the
server side !!!
• RTZen hybrid approach,
• DRTSJ , RTRMI-York, RTRMI-UPM take non-heap as a requirement
JRT-11 4

5. RTSJ region-based memory model
• Three types of memory areas :O1=new Object
– Heap
– Immortal Memory (I)
– Scoped Memory (Sx)
O1
• A selector mechanism Sa
1
– One scope stack per thread
– Enter, executeInArea Sb
O2
1
• Destruction mechanism I
– Stack discipline (counter)
• Safety mechanism Scope Stack
– Assignment rule
– Single parent rule Forbidden assignment
Default allocation
5
context

6. Calculator() Calculator()
NhRo: memory model
lastInteger lastInteger
add() add()
lastResult() lastResult()
doNothing() doNothing()
• Fragmented memory model
– Creation Context
• Represents the state of the remote object
– Invocation Context
• Objects created during remote invocation
• Safe nesting of contexts
– NhRo-rule: references from creation to invocation are
forbidden
– References from invocation to creation are allowed
6

7. NhRo:
Example
JRT-11 7

8. NhRo: Impact on the middleware
Scoped or Immortal
CalculatorImpl_Stub CalculatorImpl
lastInteger
add() add()
lastResult() lastResult()
doNothing() doNothing() Programmer
Layer
ObjId Ref CC
Invocation max
Invocation 1
CalcID
Immortal memory
0
0
Remote Object Table Thread Memory Area
Pool Pool Middleware
Layer
JRMP/IIOP
Transport Transport
RTSJ
Virtual
Machine
Client Server
8

9. NhRo in action
Calculator() Creation Context
lastInteger
(Immortal Memory)
add()
lastResult() Invoc. Context
doNothing()
(LTMemory)
CalcID Ref
OBJId Table
enter
0 0 1
0
Thread Memory Area objID a b
pool pool
meth tmp ser
1
Transport
CalcID.add(DataInt(3),DataInt(4)) Middleware
Program
DataInt(7) created created
object object 9

10. NhRo vs. traditional
GC’d remote objects
Garbage collector RTSJ-RI Memory area pool Garbage collector RTSJ-RI Memory area pool
8
16
7
14
6
Consummed time (ms)
12
Consummed time (ms)
5
10
4
8
3
6
2 4
1 2
0 0
1 21 41 61 81 101 121 141
752
1286
1910
2534
3158
sample
Alive memory (kB)
JRT-11 10

11. Enhancements to the basic NhRo
model
• Patterns for programming with NhRos
• NhRo stored in scoped memory
– Scope stack characterization
– Changes in the middleware
– Policies for the memory are pool
• Performance issues
– Dependency on data transmitted
JRT-11 11

12. Calculator()
NhRo: constraints (I)
lastInteger
add()
lastResult()
doNothing()
• NhRo-rule limitations
– Objects is creation context are destroyed after
remote invocation by default
• Two patterns to avoid the problem
– Copy pattern
– Extended portals
12

13. NhRo: Scope Stack at the server
Invocation
context
:RO1=new RemoteObject Sinv1 a b
Handler 1
Thread
Sa RO1 Sa RO1
Creation context
Creation context
1 1
Sb Sb 1
1
I I
Scope Stack Scope Stack
(during remote object creation) (during remote invocation)
• Creation context: state of the remote object
• Invocation context: parameters of remote invocation 13

14. Decoupling middleware
implemenation from NhRos
JRT-11 14

15. Invocationnumber
Memory Area Pool
Invocationsize
0 0 0
Memory Area
• It stores LTMemory instances only Pool
• It requires two configuration parameters
– Number of instances in the pool
– Memory associated to each invocation context
• Auto-collection
– Invocation context returns automatically to its pool when
they are not used
• Internal counter 1→0
• Avoids memory area leakage
15

16. bytes
5000
0
10000
15000
20000
25000
30000
void
boolean
byte
char
short
int
long
float
double
null
Byte
Short
Integer
Long
Float
Double
Character
X
Boolean
RtUnRemOb
String()
JRT-11
String(10)
and LTMemory size
String(25)
String(50)
String(100)
Object[0]
Object[10D]
Object[25D]
Object[50D]
Object[100D]
Vector(0)
Vector(10D)
Vector(25D)
Vector(50D)
Vector(100D)
Remove invocation parameters
X echo(X)
X doNothing()
void doNothing(X)
16

17. NhRos vs. (RT*) Garbage Collectors [new]
JRT-11 17

18. Conclusions
• This work has introduced a model able to remove
the garbage collection from the end-to-end path
– NhRo model
• Empirical results showed:
– Its implementation in basic environments is simple
– The performance patterns offered are powerful
JRT-11 18

19. Ongoing Work-
• To produce an analytic model for the NhRo
– Use of heap, and different threads
– Identification of useful combinations
• Analyze the parentage-rules proposed by Higuera-
Toledano and integrate them with NhRos
– A more restricted model
JRT-11 19

20. JRT-11 20