[Glass] GsDevKit Server Blocks for Thin Client appications ... pre-announcement
Dale Henrichs via Glass
glass at lists.gemtalksystems.com
Sat Apr 18 20:54:11 PDT 2015
Sebastian,
Follow these directions to do use the server blocks install[1] ... for
best results right now follow all of the steps with a fresh clone so
you'll get the right checkout of gsDevKitHome and tODE ... the standard
installs are written to work with the master branches, but both projects
are in development ... part of the installation instructions arrange for
you to load the dev branch of tode in both pharo and gemstone...
Dale
[1]
https://github.com/GsDevKit/gsDevKitHome/blob/dev/projects/roassal/devBootstrap.md#roassal-visualization-setup-and-install
On 4/18/15 6:51 PM, Sebastian Heidbrink via Glass wrote:
> Hi Dale,
>
> which are the branches on has to load in order to get this package in
> a tODE image?
>
> I am missing he TDShell forSessionNamed: method.
>
> Am I right that this would be the implementation?
> TDShell class >>
> forSessionNamed: aSessionName
> ^ self sessionDescription: (TDSessionDescription importFrom: self
> sessionDescriptionHome, aSessionName)
>
> Cheers
> Sebastian
>
>
> On 2015-04-15 10:23 PM, Dale Henrichs via Glass wrote:
>> A GsDevKit Server Block[1] is a block that is written in-line in
>> client Smalltalk, but is executed in GemStone. For example the
>> following expression is executed in a standard Pharo workspace:
>>
>> | shell x y |
>> shell := TDShell forSessionNamed: 'devKit'.
>> x := 3.
>> y := 4.
>> shell onServerDo: [ x + y ].
>>
>> and the `[3 + 4 ]` block is executed in GemStone using the `devKit`
>> session description to log into the stone. The temp vars x and y
>> referenced in the server block and defined in Pharo are shipped
>> across the wire to GemStone along with block source where the block
>> source is compiled and executed. The result is then shipped back
>> across the wire and returned as the result of #onServerDo: message in
>> Pharo. Pharo execution can continue on using the result. STON[2] is
>> used to serialize the objects that are shipped across the wire.
>>
>> For any of you familiar with underpinnings of GemTools, Jade or tODE,
>> this is not necessarily ground-breaking technology, however, exposing
>> this capability to developers just may be.
>>
>> It has been a long standing crime that developers in the Pharo
>> community choose to use MongoDB and MySQL over GemStone, but frankly
>> the problem is that (until now) we have not had a simple client-based
>> solution for adding GemStone-based persistence for native Pharo
>> applications - the pharo developers have not really had a choice.
>>
>> Being able to embed server blocks in client code certainly qualifies
>> as simple. Solution(?), well that remains to be seen, but I am
>> optimistic.
>>
>> As a more concrete example, here's Pharo workspace code that uses
>> NeoCSV running in Pharo to load stone objects in a Dictionary in
>> GemStone:
>>
>> 'NeoCSVBenchmark.csv' asFileReference
>> readStreamDo: [ :stream |
>> | reader converter buffer bufCnt numRecords records |
>> converter := [ :string | NeoNumberParser parse: string ].
>> reader := NeoCSVReader on: (ZnBufferedReadStream on: stream).
>> reader
>> recordClass: NeoCSVTestObject;
>> addIntegerField: #'x:';
>> addIntegerField: #'y:';
>> addIntegerField: #'z:'.
>> buffer := Array new: 1000.
>> bufCnt := 0.
>> [ reader atEnd ]
>> whileFalse: [
>> bufCnt := bufCnt + 1.
>> buffer at: bufCnt put: reader next.
>> bufCnt = buffer size
>> ifTrue: [
>> numRecords := bufCnt.
>> records := buffer.
>> DevKitShell
>> onServerDo: [
>> 1 to: numRecords do: [ :index |
>> | record |
>> record := records at: index.
>> NeoCSVDictionary at: record x put: record ].
>> System commitTransaction.
>> nil ].
>> bufCnt := 0 ] ] ].
>> DevKitShell onServerDo: [ System commitTransaction ]
>>
>> The code ships 1000 instances of NeoCSVTestObject at a pop to
>> GemStone. Using the above technique, one can easily arrange to store
>> some pretty large object graphs in GemStone ... Efficient queries
>> based on standard Smalltalk can be written on the client and
>> transparently performed in GemStone (see the GsDevKitServerBlocks
>> doc[1] for the complete example).
>>
>> Server blocks do not duplicate the functionality GemBuilder for
>> Smalltalk[6][7] which provides transparent replication and
>> maintenance of objects between the client and server. With server
>> blocks you end up with disconnected copies of server objects.
>>
>> Because of this disconnect, I think the best way to architect an
>> application using server blocks, is to plan on "executing all
>> business logic" on the server --- If you are using an MVC pattern,
>> the M would primarily be managed on the server while the VC would be
>> managed on the client.
>>
>> As an application evolves, the code can migrate back and forth
>> between client and server as needed.
>>
>> Most of the server blocks code leverages tODE and has been in use for
>> several years. The code that spelunks in the block structure and
>> extracts the _value_ of temp variables is only a couple of days old
>> and has some pretty rough edges (notice the odd placement of temp
>> variables and declarations in the above example).
>>
>> The server-side debugger and inspectors, etc. will use tODE (at least
>> for now) ... in the server blocks doc[1] I demonstrate an
>> #exportClassToServer: to illustrate the potential to share code in
>> weird and wonderful ways between the client and server.
>>
>> If you have the interest/opportunity to take this code for a spin,
>> let me know. I have written instructions[5] for installing the
>> experimental Roassal Visualization code[4] (GemStone and Pharo3.0 or
>> Pharo4.0) for Pierre Chanson and those instructions can be used for
>> doing work with GsDevKit
>> Server Blocks. There are a handful of obvious things that need to be
>> done:
>> - connection pools
>> - coordinated client/server debuggers
>> - client-side exception handlers for server errors
>> - more???
>> and if folks express interest in start to do exploratory work with
>> server blocks, then I will make time to provide support.
>>
>> I am hoping to have something to announce by Smalltalks in
>> November,so it would be useful if some experienced GemStoners tried
>> things out before then...
>>
>> I do have to finish up the documentation for GsDevKitHome 1.0.0 and
>> tODE 0.1.0 and I'm also committed to doing some work on the 3.3
>> GemStone release, so we'll see how that goes:)
>>
>> I also think that server blocks can be very useful for the "develop
>> in Pharo, deploy in GemSstone" crowd, since it will be possible to
>> write "pharo-based scripts" to perform server-side tasks ...
>>
>> Questions or comments?
>>
>> Dale
>>
>> [1]
>> https://github.com/GsDevKit/gsDevKitHome/blob/dev/docs/articles/gsDevKitServerBlocks.md#gsdevkit-server-blocks
>> [2] https://github.com/GsDevKit/ston#ston---smalltalk-object-notation
>> [3] https://vimeo.com/123261640
>> [4]
>> https://github.com/GsDevKit/gsDevKitHome/tree/dev/projects/roassal#roassal-visualization
>> [5]
>> https://github.com/GsDevKit/gsDevKitHome/blob/dev/projects/roassal/devBootstrap.md
>> [6] http://gemtalksystems.com/products/gbs-vw/
>> [7] http://gemtalksystems.com/products/gbs-va/
>>
>>
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