wiring hacker synapses

8/14/2019 Wiring Hacker Synapses

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Wiring Hacker Synapses

Mustafa K. Isikcodesurgeonblog.com

Scott Lewiscomposent.com

Eclipse Communication FrameworkEclipseDay at the GoogleplexJune 24th, 2008Mountain View, CA


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Who has seen the

screencast?


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4/28

Collaborative Coding andTeam Tooling in Eclipse


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Collaborative Coding

Real-Time Shared Editing with Cola

Motivation

Conceptual Overview

Challenges

Solutions

The Future


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Motivation

Enable Pair Programming

Live Code Review

Help, Tutor, Mentor

Tap into Domain/API Knowledge

Independent of Geographic Restrictions

Resilient to Location Limitations


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Make Coding More Social,Effective & Fun


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Conceptual Overview

2 Participants working on the samedocument

text file, java source code, etc.

On different machines

changes sent over the network

Consistent document state

No unintended changes


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Conflict Free IdealAnna Zo

time

ins(a)

index a

ins(a)

initial consistent doc initial consistent doc

index a

ins(a)

ins(0)

ins(a)ins(0)

index 0ins(a)ins(0)

index 0


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ReviewAnna Zo

time


Some Editing

Consistent Documents

Intention Preserving Changes


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Review (cont.) No conflicts because

Anna generates change on common documentstate, sends to Zo

Zo updates unmodified local doc withincoming change

Zo generates change on updated document,

sends to Anna

Anna updates common doc state with incomingchange

Strictly Sequential Execution ideal, but unrealistic


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Challenge Out of Order sending/reception

time

ins(a)

index a

ins(a)

ins(0)

index 0

ins(a)ins(0)

Anna

initial consistent doc

Zo

initial consistent doc

index 0

ins(0)

index a

index 0

ins(0)

index a

ins(a)


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Solution

In-order Message sending/reception

network protocols to the rescue

build on TCP

build on application level protocol relyingon TCP, e.g. XMPP

ECF provides for abstraction fromunderlying protocol, XMPPS, Skype, etc.


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Challenge

Text Editor Responsiveness

Local changes need to be applied

immediately

Network Latency

Messages crossing on the wire

Immediate application of local changes andNetwork Latency High Probability forConflicts


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Cross-on-Wire Conflicttime

ins(a)

index a

ins(a)

Anna Zo


ins(0)

ins(a)ins(0)

index 0

index 0

ins(0)

ins(0)

index 0

ins(a)

index a


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Solution

Resolution mechanism for conflicting,mutually directed changes operationaltransformations

precondition: locally applied operationand incoming remote operation originatefrom same document state

postcondition: transformed remoteoperation ready for intention-preservingapplication to local document


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Operational

Transformations How to determine origination state/

compatibility?

stamp each locally generated operationwith counters

local operation count

remote operation count


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Operational

Transformations cont. compare counters on incoming remoteoperation & conflicting, already appliedlocal operation

cola operational transformation

input: conflicting incoming remote op &

already applied local op

output: updated remote op, ready forlocal application, e.g. index update


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Operational Transformation for Cross-on-Wire Conflict Resolution

ins(a)

index a

ins(a)

Anna Zo


ins(0)

ins(a)ins(0)

index 0

index 0

ins(0)

coopt( ) ins(a) ins(0) ins(a+L)

ins(0)

index 0 index a + L

ins(a+L)

coopt( ) ins(a)ins(0) ins(0)

updated index!no update necessary!

time


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Pseudocode:

Resolving Cross-On-Wire//assert operation compatibility, i.e. sameorigination state

Assert.isTrue(

localOp.sentCount == remoteOp.receivedCount );

if ( localOp.isIns && remoteOp.isIns ) {if( localOp.index < remoteOp.index){

//move remoteOp.index right by length oflocalOp

} else if (localOp.index == remoteOp.index) {

//notion of docOwner, consistently clarify

preference} else if (localOp.index > remoteOp.index) {

//do nothing to remote op, apply withoutmodification

}

}


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Combinatorial

Ex losion Determine atomic operations, e.g. del, ins

to be transformed against each other

The fewer the better

model compound operations from simple

ones (e.g. replacement as deletion andinsertion)


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Divergence by More

than one O eration Generation of multiple local changes while

remote operation is traveling

that is: upon arrival of remote operation,local doc changed by more than locallyapplied operation

precondition for operationaltransformation not met


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Divergence by More than One

Op. (cont.)ins(a)

ins(a)

Anna Zo


time

ins(v)

ins(a) ins(v)

ins(z)

ins(z)

coopt( ? ) ?ins(z)

ins(a) ins(z)

coopt( ) ins(a) ins(z) ins(a)

no update necessary!

coopt( ) ins(z)ins(v) ins(v)


ins(a) ins(z)ins(v)


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coopt( ) where y = x + Length of

ins(x) ins(v)

ins(v)

Resolution

ins(a)

ins(a)

Anna Zo


time

ins(v)

ins(a) ins(v)

ins(z)

ins(z)

ins(a) ins(z)

coopt( ) ins(a) ins(z) ins(a)


coopt( ) ins(z)ins(v) ins(v)


ins(a) ins(z)ins(v)

coopt( )

where x = z + Length of

ins(z) ins(a)

ins(a)

ins(x)

ins(y)

ins(a) ins(v) ins(y)


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Additional Details Manage local queue of unacknowledgedoperations

add local operations as executed

remove local operations as implicitlyacknowledged by remote operationsappropriate counter

virtual update of queued up, appliedlocal ops properties not in this talk

Helps to introduce notion of state-space

which is being traversed

not in this talk


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The Future More than 2 session participants

Project Sharing

API for Cola and its Model for OptimisticConcurrency Control

Diagrams, anyone?

Deeper Integration

Multiple Cursors

Highlighted Areas

More on this from Scott ... time left?


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ResourcesMustafas blog http://codesurgeonblog.com

Scotts ECF blog http://eclipseecf.blogspot.com/

ECF Eclipse Wiki http://wiki.eclipse.org/Eclipse_Communication_Framework_Project

ECF Project Home http://www.eclipse.org/ecf/

Cola Screencast

http://www.vimeo.com/1195398

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