One of the features of traditional Smalltalk is that the development tools are in the same object space as the application being developed. A corollary is that it has generally been a challenge to debug a remote object space or build up a new class library from scratch. But GemStone's multi-user architecture provides some intriguing abilities to isolate not just classes, but methods. In this presentation we provide an introduction to GemStone/S and demonstrate running code from a Minimal-Pharo (with over 1400 classes) in GemStone.

1. Running Pharo on the
GemStone VM
James Foster
VP of Finance & Operations, GemTalk Systems LLC
FAST 2017 – La Plata, Argentina
8 November 2017

2. Agenda
• GemStone/S Introduction
• Replacing Base Class Libraries
• Questions
2

3. Limitations of traditional Smalltalks
• Object space (image) must fit in (virtual) RAM
• Object space visible to one (single-threaded) VM
• Sharing objects between VMs is difficult
– Convert to non-object format (binary, XML, SQL)
– No built-in object identity for multiple exports
• Object state is lost when VM exits
3

4. Welcome to the magical
world of GemStone
• Object space limited by
disk, not RAM
• Object space shared
across multiple VMs on
multiple hosts
• Transactional
persistence
• Image from
http://www.flickr.com/photos/laffy4k/182219003/
• Creative Commons License
http://creativecommons.org/licenses/by-sa/2.0/ 4

5. GemStone/S Architecture
5

6. Gem Types
• Linked Gem
– Gem in application process space
• Remote Procedure Call (RPC) Gem
– GCI library in application space
– Gem has separate process
6
Application &
GCI Library
Gem
OS Process
Gem
Application &
GCI Library TCP/IP
OS Process 1 OS Process 2

7. One-Machine Process Locations (Linked Gem)
7
Application
& GCI
Library Gem
Stone
SPC
Repository

8. One-Machine Process Locations (RPC Gem)
8
Application
& GCI
Library
Gem
Stone
SPC
Repository
NetLDI

9. Two-Machine Process Locations (Gem on Stone Host)
9
Application
& GCI
Library
Client Host
N
E
T
W
O
R
K
Gem
Stone
SPC
Repository
Stone Host
NetLDI

10. Two-Machine Process Locations (Gem Remote from Stone)
10
Application
& GCI
Library
Gem
Gem Host
Remote SPC
Page
Server
N
E
T
W
O
R
K
NetLDI
Stone
SPC
Repository
Stone Host
Page
Server
NetLDI

11. Three-Machine Process Locations
11
Application
& GCI
Library
Client Host
N
E
T
W
O
R
K
Gem
Gem Host
Remote SPC
Page
Server
N
E
T
W
O
R
K
NetLDI
Stone
SPC
Repository
Stone Host
Page
Server
NetLDI

12. Shared Page Cache
12

13. Agenda
• GemStone/S Introduction
• Replacing Base Class Libraries
• Questions
13

14. Replacing Base Class Libraries
• Smalltalk was intended to allow exploration
• Portability
– ANSI
– Grease
• Can we go to a lower level?
• One approach to learn more
14

15. Option 1: Complete Replacement
• Not possible in most Smalltalks
– Creating methods requires code
• GemStone schema editing with Topaz
– Build process starts with a few base classes
– But no methods for any class (initially)
• Challenges
– Difficult to debug (most tools are internal)
– VM has knowledge of schema
15

16. Option 2: Parallel Class Hierarchy
• GemStone’s namespace model allows separate
hierarchy
16

17. Pharo Global Lookup
17
Smalltalk
(a SmalltalkImage)
a SystemDictionary
a GlobalVariable
(Association)
globals
a CompiledMethod
a Symbolkey
an Object
value
Image

18. GemStone/S Global Lookup
18
AllUsers
(a UserProfileSet)
a UserProfile
a SymbolList
(Array)
Repository
a SymbolDictionary a SymbolAssociation
symbolList
a CompiledMethod
a Symbolkey
an Object
value

19. Unique or Shared SymbolDictionary Instances
19
AllUsers
Bob
a SymbolList
Repository
1. UserGlobals
Carol
a SymbolList
2. Globals
1. UserGlobals
3. Published
SymbolDictionary instances

20. Unique or Shared SymbolAssociation Instances
20
1. UserGlobals
assoc
#Arraykey
Array
value
2. Globals
1. UserGlobals
assoc
key
value
Bob’s SymbolList Carol’s SymbolList

21. Unique Keys
21
1. UserGlobals
assoc
#Arraykey
Array
value
2. Globals
1. UserGlobals
assoc
key
value
Bob’s SymbolList Carol’s SymbolList
#List

22. Unique Values
22
1. UserGlobals
2. Globals
1. UserGlobals
Bob’s SymbolList Carol’s SymbolList
assoc
#OrderedCollection
key
OrderedCollection
value
assoc
key
OrderedCollectionvalue

23. Problems with Parallel Class Hierarchy
• GemStone’s namespace model allows separate
hierarchy
• But complications exist:
– Literals
– Classes known to the VM
23

24. Complication: Literals (and their superclasses)
• Array: #()
• BlockClosure: []
• Boolean: true, false
• ByteArray: #[1 2 3]
• Character: $a
• Float: 1.23
• SmallInteger: 42
• String: ‘Smalltalk’
• Symbol: #Array
• UndefinedObject: nil
24

25. Complication: Classes Known to the VM
• Behavior, Class, Metaclass
• Exception, MessageNotUnderstood, ZeroDivide, …
• Pragma
• Process
• ProcessorScheduler
• So, we need to use (some) base classes
25

26. Problem: Conflicting Implementations
• Array>>printOn:
– Pharo
• #(1 2 3) printString '#(1 2 3)'
– GemStone
• #(1 2 3) printString 'anArray( 1, 2, 3)'
26

27. Option 3: Parallel Methods in GemStone Classes
• Each GemStone class has a collection of
MethodDictionary instances
– Methods are compiled into an “environment”
– Message sends to same environment (by default)
• Method environments:
0 = GemStone/S (default)
1 = Maglev (reserved for Ruby)
2+ are for others
– We use 2 for Pharo
27

28. 28
Array Array class
a MethodDictionary a MethodDictionary
Pharo Method Dictionaries
Arrayed
Collection
Arrayed
Collection class
a MethodDictionary a MethodDictionary
Sequenceable
Collection
Sequenceable
Collection class
a MethodDictionary a MethodDictionary

29. 29
Array Array class
method
dicts
a MethodDict [0]
nil
a MethodDict [2]
method
dicts
a MethodDict [0]
nil
a MethodDict [2]
GemStone Method Dictionaries - 1
Sequenceable
Collection
Sequenceable
Collection class
method
dicts
a MethodDict [0]
nil
a MethodDict [2]
method
dicts
a MethodDict [0]
nil
a MethodDict [2]

30. 30
Array Array class
method
dicts
a MethodDict [0]
nil
a MethodDict [2]
method
dicts
a MethodDict [0]
nil
a MethodDict [2]
GemStone Method Dictionaries - 2
Sequenceable
Collection
Sequenceable
Collection class
method
dicts
a MethodDict [0]
nil
a MethodDict [2]
method
dicts
a MethodDict [0]
nil
a MethodDict [2]
Arrayed
Collection
Arrayed
Collection class
method
dicts
a MethodDict [0]
nil
a MethodDict [2]
method
dicts
a MethodDict [0]
nil
a MethodDict [2]

31. Sample Messages
• Implicit
– “in env 0” #(1 2 3) printString 'anArray( 1, 2, 3)'
– “in env 2” #(1 2 3) printString '#(1 2 3)'
• Explicit
– #(1 2 3) @env0:printString 'anArray( 1, 2, 3)'
– #(1 2 3) @env2:printString '#(1 2 3)’
31
Array
method
dicts
a MethodDict [0]
nil
a MethodDict [2]
printOn: aStream
“for GemStone”
printOn: aStream
“for Pharo”

32. Problems with Using GemStone Classes
• GemStone class might have different schema
– OrderedCollection in Pharo
• Instance variables: (array firstIndex lastIndex)
– OrderedCollection in GemStone
• No instance variables
– Since OrderedCollection is not known to the
compiler, we don’t have to use GemStone’s class
32

33. Options
1. Replace all classes
But schema is wrong in some cases
And we would like to use tools during development
2. Use parallel classes exclusively
But compiler & VM know about some GemStone classes
3. Use parallel methods exclusively
But schema is different for some classes
4. Hybrid
Use GemStone classes when necessary
Use parallel classes otherwise
Use method environment 2 for everything
33

34. Tools
• Topaz
– GemStone’s command-line interface
• GemBuilder for Smalltalk (GBS)
– GemStone’s GUI IDE for VA & VW
• Others
– tODE
– gt4gemstone
– Jade
34

35. Issues
• Incomplete Class Types
– GemStone has in-memory Ephemerons, but no
Weak references
– No 32-bit objects
• GemStone compiler is in VM
– Not as easy to experiment with new syntax
• Low-level objects may need extensive rewrite
– BlockClosure, Process, ProcessorScheduler, etc.
35

36. Demo
• http://files.pharo.org/get-files/60/pharo-minimal.zip
• http://downloads.gemtalksystems.com/pub/GemStone64/3.4.0/
• https://github.com/jgfoster/PharoGs/tree/james/james
36

37. Questions?
37
GemTalk Systems LLC
15220 NW Greenbrier Pkwy., Suite 240
Beaverton, Oregon, 97006
Voice & Fax: +1 503 766 4714
james.foster@gemtalksystems.com
James G. Foster
VP of Finance & Operations
www.gemtalksystems.com
®