Toward Remote Object Coherence with Compiled Object ...engelen/cpctalk06.pdf · CPC Jan 10, 2006 1...

CPC Jan 10, 2006 1

Toward Remote ObjectCoherence with Compiled

Object Serialization forDistributed Computing with

XML Web Services

Robert van Engelen and Wei Zhang

Florida State University

Madhusudhan Govindaraju

State University of New Yorkat Binghamton

CPC Jan 10, 2006 2

Outline

Motivation:is object-level coherence in XML Web services feasible?

XML serialization:the good, the bad, and the ugly

The gSOAP project:a compiled serialization approach for intercommunication

Results and conclusions

CPC Jan 10, 2006 3

Motivation

“Compiler techniques are necessary toimprove speed and ensure object coherence

in XML-based distributed computing”

CPC Jan 10, 2006 4

Motivation (cont’d)

Object serialization has increasingly becomemore powerful and popular as a means to builddistributed systems Typically based on remote procedure call (RPC) or

its OO equivalent remote method invocation (RMI)

XML is gaining popularity as a serialization format

Message-passing interfaces are also popular, buttheir low-level APIs are not designed to exchangecompound data types and entire object graphs

CPC Jan 10, 2006 5

The Good:a Case for XML Serialization

XML serialization (e.g. used by XML Web services)is gaining popularity, because:+ Binary serialization protocols are inflexible, while XML

is an extensible format that supports compositionality

+ Binary serialization protocols do not interoperate wellacross platforms and through firewalls

+ Hierarchical business data is easily expressed in XML

+ Significant proliferation of XML warehousing

+ Newer generation of office tools use XML-baseddocument formats

CPC Jan 10, 2006 6

The Bad:XML Serialization Issues

XML serialization has shortcomings:– How bad does XML serialization impact

performance and network bandwidth?

– “XML = trees”, so how can XML be used to serializeobject graphs and ensure object-level coherence?

Can compiler techniques help to mitigate theseconcerns?

CPC Jan 10, 2006 7

The Ugly:SOAP RPC Encoding

Plain-old XML to serialize object graphs won’t work:– Naïve approach serializes object graphs into XML trees

(this is fine with business data and most numerical data)

– No standard object referencing mechanism to implementgraph edges of object graphs

– No namespaces to distinguish objects that share thesame name but are structurally different

SOAP RPC encoding standard supports object graphs!

CPC Jan 10, 2006 8

The Ugly (2):SOAP RPC Encoding

XML namespaces to separateoperations and type definitions

The XSD type system to representvalues of primitive types in XML,such as bool, integer, float, string,base64

A new XML array type to encodesparse and partial arrays

Id-href XML attributes toimplement graph edges to encodemulti-ref objects

<env:Envelope> <env:Body env:encodingStyle=“…”> <ns:myRemoteOp> <arg1 xsi:type=“xsd:int”>123</arg1> <arg2 enc:arrayType=“xsd:string[5]”> <item>abc</item> <item href=“#_1”/> <item href=“#_1”/> <item enc:position=“[5]”>xyz</item> </arg2> </ns:myRemoteOp> <mref id=“_1”>def</mref> </env:Body></env:Envelope>

CPC Jan 10, 2006 9

The Ugly (3):SOAP RPC Encoding

At first glance this looks promising, but …– Serialization is still lossy when floating point values

are encoded in text form (due to roundoff)

– No requirements on multi-ref encoding with id-href:

no assurance that the logical structure of an object

graph is unchanged at the receiving side

– Encodes XML with only forward pointing references

to multi-referenced nodes (fixed in SOAP 1.2)

CPC Jan 10, 2006 10

The Ugly (4):SOAP Document/literal Style

More problems with SOAP document/literal style:– Document/literal style requires support for the entire XML

Schema standard, but XML Schemas are intended forvalidation and not for data modeling

– “Impedance mismatch”: programming language typesystems are different than XML schema’s type system

– No default fall-back referencing mechanism such as id-href to implement graph edges, but can use staticdefinition of optional graph edges for each data type

CPC Jan 10, 2006 11

XML Web Services

Object

graph x

Send request

Object

graph

XML

XML Serialization XML Deserialization

Object

graph y

Receive request

Object

graph x’

Receive response

Object

graph

XML

XML Deserialization XML Serialization

Object

graph y’

Send response

Server:transform y

into y’

Client Server

CPC Jan 10, 2006 12

Web Service Tools:Lossy Serialization in XML

Object

graph x

Internal binary format X

Object

graph y

XML

XML Serialization

XML Deserialization

Serialization in XML can be lossy, because object graph x cannot be recoveredfrom its serialized XML form if we are not careful about the choice of mapping

CPC Jan 10, 2006 13

Basic Requirement:Object Graph Isomorphism

Object

graph x

Representation X

Object

graph y

Representation Y

Mapping M

Inverse mapping M -1

Object graphs x and y are isomorph if M is bijective and has an inverse M-1

Object-level coherence requires bijective mappings, so that distributedand serialized object graphs are always isomorph

CPC Jan 10, 2006 14

Object Coherence RequiresLossless XML Serialization

Object

graph x

Internal binary format X

Object

graph y

XML

Serialization method M

Deserialization method M -1

Serialization is lossless if an object graph x can be recovered from itsserialized XML form y = M(x) by deserializing x = M-1(y)

We consider structural equivalence only (location in memory is irrelevant)e.g. as in JavaRMI, IIOP, and DCOM

CPC Jan 10, 2006 15

Compiled XML Serialization

Points-toanalysis

Ptr hash table(graph edges)

XML engineOptimizedserializer

XMLstream

Compiler

Source codetype definitions

generates generates

XML schemadefinitions

CPC Jan 10, 2006 16

Compiled XML Deserialization

Pointerremapper

Id hash table(resolve id-ref)

XML tokenizerLL(1) parser

& deserializerXML

stream

Compiler


generates

Look-asidebuffers (cache)

CPC Jan 10, 2006 17

Static Structure Analysis forSOAP RPC Encoding

<x> <x href=“456”/> … <x href=“456”/> …</x>…<mref id=“456”>…</mref>

<x> <y href=“123”/> … <y href=“123”/> …</x>…<mref id=“123”>…</mref>

<x> <y>…</y> <z>…</z> …</x>

ExampleXML

Instance

<complexType name=“X”> <sequence>…</sequence></complexType

<complexType name=“X”> <sequence>…</sequence></complexType><complexType name=“Y”> <sequence>…</sequence></complexType

<complexType name=“X”> <sequence> <element name=“y” type=“tns:Y”/> <element name=“z” type=“tns:Z”/> </sequence> …</complexType>

XMLSchema

Structure

X

Y Z

X

Y

X X

X

X

CPC Jan 10, 2006 18

Static Structure Analysis forDocument/Literal Encoding

<x ref=“456”>…</x>…<x ref=“456”>…</x>…<x id=“456”>…</x>

<x ref=“123”>…</x>…<x ref=“123”>…</x>…<y id=“123”>…</y>

<x> <y>…</y> <z>…</z> …</x>

ExampleXML

Instance

<complexType name=“X”> <sequence>…</sequence> <attribute name=“id” type=“ID”/> <attribute name=“ref” type=“REF”/></complexType

<complexType name=“X”> <sequence>…</sequence> <attribute name=“ref” type=“REF”/></complexType><complexType name=“Y”> <sequence>…</sequence> <attribute name=“id” type=“ID”/></complexType

<complexType name=“X”> <sequence> <element name=“y” type=“tns:Y”/> <element name=“z” type=“tns:Z”/> </sequence> …</complexType>

XMLSchema

Structure

X

Y Z

X

Y

X X

X

X

CPC Jan 10, 2006 19

Static Structure Analysis forCompiled XML Serialization

Construct a data model Compiler determines which

data type instances canrefer to other data typeinstances at run time

Generate type-specific points-to analysis algorithm Only needed for pointer

types and structs/classeswith pointer fields

Generate type-specificoptimized serialization code Serializer uses id-ref linking

based on pointer analysis

Points-toanalysis

Optimizedserializer

Compiler


generates generates

Ptr hash table(graph edges)

CPC Jan 10, 2006 20

Constructing a Plausible DataModel from Source Code

typedef int SSN;

struct Node{ int val; int *ptr; float num; struct Node *next;};

val ptr num next

Node

SSN

Data model graph(arcs denote all possible

pointer references)

Source code typedefinitions

CPC Jan 10, 2006 21

Generating an XML SchemaDefinition for Serialized XML

val ptr num next

Node

SSN

<simpleType name=“SSN”> <restriction base=“int”/></simpleType>

<complexType name=“Node”> <sequence> <element name=“val” type=“int”/> <element name=“ptr” type=“int” minOccurs=“0”/> <element name=“num” type=“float”/> <element name=“next” type=“tns:Node” minOccurs=“0”/> </sequence></complexType>Data model graph

CPC Jan 10, 2006 22

Generating Code for RuntimePoints-To Analysis

serialize_pointerToint(int *p){ if (p != NULL) { // lookup and mark (p,TYPE_int) // as target in ptr hash table }}

serialize_Node(struct Node *p){ if (p != NULL) { // lookup and mark (p,TYPE_Node) // as target in ptr hash table mark_embedded(&p->val,TYPE_int); serialize_pointerToint(p->ptr); // skip p->num serialize_pointerToNode(p->next); }}

val ptr num next

Node

SSN

Data model graph

CPC Jan 10, 2006 23

Generating Serialization Codeput_pointerToint(int *p){ if (p != NULL) { // lookup (p,TYPE_int) // if embedded, then output “ref” // if single, then output value // if multi, then output value // with “id” and mark embedded }}

put_Node(struct Node *p){ if (p != NULL) { // lookup (p,TYPE_Node) // if embedded, then output “ref” // if single, then output value // if multi, then output value // with “id” and mark embedded put_int(&p->val); put_pointerToint(p->ptr); put_float(&p->num) put_pointerToNode(p->next); }}

val ptr num next

Node

SSN

CPC Jan 10, 2006 24

Serialization Example

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=B

single14intC4

single116NodeB3

embedded14intB2

multi216NodeA1

RefTypePtrCountPtrSizePtrTypePtrLocID

Ptr hash table after runtime points-to analysis by thegenerated algorithm constructed from the data model

CPC Jan 10, 2006 25

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=Bembedded, id=2

multi, id=1

single

single

multi, id=1

CPC Jan 10, 2006 26

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=B

<Node id=“_1”> </Node>

embedded, id=2

multi, id=1

single

single

multi, id=1

CPC Jan 10, 2006 27

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=B

<Node id=“_1”> <val>123</val> </Node>

embedded, id=2

multi, id=1

single

single

multi, id=1

CPC Jan 10, 2006 28

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=B

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> </Node>

embedded, id=2

multi, id=1

single

single

multi, id=1

CPC Jan 10, 2006 29

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=B

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num> </Node>

embedded, id=2

multi, id=1

single

single

multi, id=1

CPC Jan 10, 2006 30

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=B

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num> <next>

</next> </Node>

embedded, id=2

multi, id=1

single

single

multi, id=1

CPC Jan 10, 2006 31

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=B

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num> <next> <val id=“_2”>456</val> </next>

</Node>

embedded, id=2

multi, id=1

single

single

multi, id=1

CPC Jan 10, 2006 32

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=B

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num> <next> <val id=“_2”>456</val> <ptr>789</ptr> </next>

</Node>

embedded, id=2

multi, id=1

single

single

multi, id=1

CPC Jan 10, 2006 33

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=B

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num> <next> <val id=“_2”>456</val> <ptr>789</ptr> <num>2.3</num> </next>

</Node>

embedded, id=2

multi, id=1

single

single

multi, id=1

CPC Jan 10, 2006 34

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=B

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num> <next> <val id=“_2”>456</val> <ptr>789</ptr> <num>2.3</num> <next ref=“#_1”/> </next>

</Node>

embedded, id=2

multi, id=1

single

single

multi, id=1

CPC Jan 10, 2006 35

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Nodeloc=A

SSNloc=C

val=456

ptr=C

num=2.3

next=A

Nodeloc=B

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num> <next> <val id=“_2”>456</val> <ptr>789</ptr> <num>2.3</num> <next ref=“#_1”/> </next></Node>

embedded, id=2

multi, id=1

single

single

multi, id=1

CPC Jan 10, 2006 36

Compiled XML Deserialization

For each data type, generateoptimized deserialization code: Generate a recursive descent

LL(1) XML parser that isoptimized for the data type

Embed deserializationoperations as semantic actionsin the parser

Invoke id hash table lookups assemantic actions to resolve id-ref references on the fly

The pointer remapper ensures theconsistency of pointers in theobject graph when nodes aremoved in the construction process

Pointerremapper

Id hash table(resolve id-ref)

LL(1) parser & deserializer

Compiler


generates

CPC Jan 10, 2006 37

Deserialization Example<Node id=“_1”> </Node>

val=?

ptr=?

num=?

next=?

Nodeid=1

Recursive descent parsingwith object deserializationoperations as semantic actions

CPC Jan 10, 2006 38

Example (cont’d)

val=123

ptr=?

num=?

next=?

Node

<Node id=“_1”> <val>123</val> </Node>

id=1


CPC Jan 10, 2006 39

Example (cont’d)

val=123

ptr=?

num=?

next=?

Node

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> </Node>

id=1

ref=2(unresolved)


CPC Jan 10, 2006 40

Example (cont’d)

val=123

ptr=?

num=1.4

next=?

Node

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num>

</Node>

id=1

ref=2(unresolved)


CPC Jan 10, 2006 41

Example (cont’d)

val=123

ptr=?

num=1.4

next=B

Node

val=?

ptr=?

num=?

next=?

Node

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num> <next> </next></Node>

id=1

ref=2(unresolved)


CPC Jan 10, 2006 42

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

Node

val=456

ptr=?

num=?

next=?

Node

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num> <next> <val id=“_2”>456</val> </next></Node>

id=1

id=2


CPC Jan 10, 2006 43

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Node

SSN

val=456

ptr=C

num=?

next=?

Node

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num> <next> <val id=“_2”>456</val> <ptr>789</ptr>

</next></Node>

id=1

id=2


CPC Jan 10, 2006 44

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Node

SSN

val=456

ptr=C

num=2.3

next=?

Node

<Node id=“_1”> <val>123</val> <ptr ref=“#_2”/> <num>1.4</num> <next> <val id=“_2”>456</val> <ptr>789</ptr> <num>2.3</num>

</next></Node>

id=1

id=2


CPC Jan 10, 2006 45

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Node

SSN

val=456

ptr=C

num=2.3

next=A

Node


id=1


CPC Jan 10, 2006 46

Example (cont’d)

val=123

ptr=B

num=1.4

next=B

=789

Node

SSN

val=456

ptr=C

num=2.3

next=A

Node


id=1


CPC Jan 10, 2006 47

Implementation: the gSOAP Toolkit

Web service applicationsare build in two stages:1. Generate service

definitions in familiarC/C++ header file format

2. Generate client/serverstubs and skeletonsource code andserialization code

Note: the soapcpp2compiler can also beused to generate WSDLfrom header files

soapClient.cppsoapServer.cppsoapC.cpp

wsdl2h tool

soapcpp2compiler

Service defs:service.wsdl

Header file defs:service.h

CPC Jan 10, 2006 48

1. Analyze WSDL/Schema andGenerate C/C++ Header File


wsdl2h tool

Documented methods and class diagrams

Service defs:service.wsdl

CPC Jan 10, 2006 49

2. Analyze Header File andGenerate Stubs and Serializers

stats

Network fabric

gSOAP engineHTTP/S + TCP/IP + UDP

schema-optserializer

schema-optdeserializer

LL(1) XML parsersand (de)serializers

client/server API

gSOAP application

logging

WSSE

Plugins

Native C/C++ data

XML data

soapcpp2compiler

soapClient.cppsoapServer.cppsoapC.cpp


CPC Jan 10, 2006 50

Performance Results3241 callsper second

gSOAP serialization+deserialization perf. with 1.2K structures

CPC Jan 10, 2006 51

Performance Comparison toOther XML Parsers

Experimental parsers

CPC Jan 10, 2006 52

Conclusions

Is XML serialization a viable alternative to binaryserialization protocols?+ It has the advantages of cross-platform interoperability

and flexibility to manipulate XML with tools such as XSLT,filters, data mining, persistent storage, etc.

– Disadvantage is that naïve serialization can be lossy,implying object-level coherence issues

– Disadvantage is the low performance of XML parsers

+ However, compiled serialization speedup is significant

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