[Pharo-dev] How does Metacello decide what is already loaded ?

Sven Van Caekenberghe sven at stfx.eu
Fri Feb 15 17:19:04 EST 2019


Hi Dale,

Thanks for the explanation.

For now I managed to do what I wanted, using #onConflict #useLoaded I could prevent a dependencies' ConfigurationOf from going over a BaselineOf with the same name.

Sven

> On 15 Feb 2019, at 01:50, Dale Henrichs <dale.henrichs at gemtalksystems.com> wrote:
> 
> 
> 
> On 2/14/19 11:28 AM, Sven Van Caekenberghe wrote:
>> OK, where is the registry, how does it work, where can I read about it ?
> `MetacelloProjectRegistration registry` ... It is a private registry of loaded baselines and configurations used by Metacello. It's been around roughly 6-7 years or so (ever since I added git       support to Metacello and when I create the `Metacello new` style of launching Metacello loads)  ... 6-7 years ago I wrote a first cut of documentation that Torsten references, but at that time no one cared about the features I had added to Metacello, because, well they pretty much applied to git-based support and using and the `Metacello new` style of launching Metacello and  it was hard enought to get folks to use `Metacello new` by itself, let alone any of the "new features" ...
> 
> Metacello started out (2009) supporting Monticello repositories (ConfigurationOf) and then transitioned (2012)  to supporting git repositories (BaselineOf). Much of the complexity in Metacello is a carry over from Monticello support ... and isn't really needed.
> 
> Today (2018) I am working on Rowan which is/will be a wholesale replacement for Monticello/Metacello and the specifications for what packages will be loaded is simplified quite a bit ... 
> 
> So it is a bit ironic, that real interest in how Metacello works comes at a time when I am well on my way to finishing a replacement for Metacello:) Okay this is not entirely true ... over the years I have been quizzed by folks and if you look through the pharo mailing list archives, you'll probably see that I've written a few long-winded mails answering questions or trying to describe how things work:)
> 
>> 
>> Let's make this more concrete: I load Bootstrap which will load Seaside and I load Material Design Lite which will load Seaside. Will Seaside be loaded twice ? On what does this depend ? How can we as a community make sure we are talking about the same Seaside ?
>> 
>> That is essentially my question.
>> 
>> I know it is not an easy question, but I find it an important one.
>> 
> First there is the Monticello "mcz file" answer, which applies to real .mcz files and filetree repositories with Monticello meta data.
> The simplest case is a project without dependencies.
> 
> When a Metacello load is kicked off, Metacello evaluates the configuration or baseline specification and determines the  list of packages in load order that are needed to satisfy the specification. Metacello then traverses the list and compares the mcz version of the Monticello package working copy in the image with the mcz version of the Monticello package on disk those Monticello packages that are newer than the loaded packages are then loaded into the image .... (how the packages are loaded is dependent upon whether not using are using #atomic or #linear loads).
> 
> If there is a project dependency, Metacello determines the version of the project that is loaded in the image (looking in the registry) and compares that to the incoming version of the project. If the incoming project version is greater than or equal to the loaded project (this is a simplification of reality, since individual loads can be customized to allow or disallow a number of conflicts and or default decisions made by Metacello), the packages from the dependent project are added to the list of packages in load order ...
> 
> This process is repeated until all dependent projects are accounted for ... 
> 
> If a dependency loop is encountered as you suggest, Metacello will choose to load the latest version of the dependent project ...
> 
> In general Metacello loads the latest version of a project encountered and the latest version of package encountered ... 
> 
> If you inspect/print the result `Metacello new ... record` you will see a collection of load directives, which details which packages will be loaded the order that they will be loaded. 
> 
> Here's an example printed load directive from a GemStone image I happen to have open (Seaside is not loaded):
> 
> [ Metacello new
>  baseline: 'Seaside3'; record ] on: Warning do: [:ex | ex resume ].
> 
>  linear load : 
> 	linear load : baseline [BaselineOfSeaside3]
> 		load : BaselineOfGLASS1
> 	linear load : baseline [BaselineOfSeaside3]
> 		load : BaselineOfGrease
> 	linear load : baseline [BaselineOfSeaside3]
> 		load : BaselineOfGrease
> 	linear load : baseline [BaselineOfSeaside3]
> 		linear load : baseline [BaselineOfGLASS1]
> 			load : BaselineOfGrease
> 		linear load : baseline [BaselineOfGLASS1]
> 			load : BaselineOfMetacello
> 		linear load : baseline [BaselineOfGLASS1]
> 			linear load : 1.0-alpha2.2 [ConfigurationOfGoferProjectLoader]
> 			load : Network-Url
> 			linear load : baseline [BaselineOfGrease]
> 				atomic load : 0.250 [ConfigurationOfGsCore]
> 					load : Network-Url-dkh.2
> 				atomic load : 0.243 [ConfigurationOfGsMisc]
> 				load : Grease-Core
> 				atomic load : 0.243 [ConfigurationOfGsMisc]
> 				atomic load : 0.243 [ConfigurationOfGsMisc]
> 				load : Grease-GemStone-Core
> 				load : Grease-GemStone330-Core
> 				load : Grease-Tests-Core
> 				load : Grease-Tests-GemStone-Core.v32
> 			linear load : baseline [BaselineOfMetacello]
> 				load : BaselineOfFileTree
> 			linear load : baseline [BaselineOfMetacello]
> 				load : Metacello-Base
> 				load : Metacello-Core
> 				load : Metacello-MC
> 				load : Metacello-Platform.gemstone
> 				load : Metacello-ToolBox
> 				load : Metacello-Cypress
> 				load : Metacello-Tutorial
> 				load : Metacello-TestsCore
> 				load : Metacello-TestsMCResources
> 				load : Metacello-TestsCommonMC.common
> 				load : Metacello-TestsMCCore
> 				load : Metacello-TestsTutorial
> 				linear load : baseline [BaselineOfFileTree]
> 					load : MonticelloFileTree-Core
> 					load : MonticelloFileTree-FileDirectory-Utilities
> 				load : Metacello-GS3x-Platform
> 				load : Metacello-FileTree
> 				load : Metacello-GitBasedRepository
> 				load : Metacello-GitHub
> 				load : Metacello-Bitbucket
> 				load : Metacello-Reference
> 				load : Metacello-TestsReference
> 				load : Metacello-TestsMC
> 				load : Metacello-TestsMCB
> 				load : Metacello-TestsCypress
> 				load : Metacello-TestsMCA
> 				load : Metacello-TestsPlatform.gemstone
> 				load : Metacello-GemStone-TestsMCB
> 			load : GemStone-Interactions
> 			load : Core.v3
> 			load : GemStone-Compression
> 			load : Core322x
> 			load : Base-Bootstrap.v3
> 			load : Bootstrap.v34
> 			load : GemStone-ANSI-Streams
> 			load : GemStone-Indexing-Extensions.v34
> 			load : OmniBrowser
> 			load : OB-GemStone-Platform
> 			load : Squeak.v34
> 			load : Regex-Core
> 			load : Regex-Tests-Core
> 			load : GsSqueakCommon-Core
> 			load : GsSqueakCommon-CoreV30
> 			load : PackageInfo-Base.g
> 			load : Monticello.v34
> 			load : MonticelloGs.v33
> 			load : GemStone-Deployment.v310
> 			load : Change-Notification.v310
> 			load : OB-Standard.v3
> 			load : OB-Monticello
> 			load : OB-SymbolListBrowser
> 			load : OB-SUnitIntegration
> 			load : OB-SUnitGUI.g
> 			load : Announcements
> 			load : OB-Tools.v33
> 			load : JadeServer
> 			load : GemStone-Release-Support
> 		load : Seaside-Squeak-Compatibility
> 		linear load : baseline [BaselineOfGrease]
> 			atomic load : 0.250 [ConfigurationOfGsCore]
> 				load : Core.v3-dkh.78
> 				load : Core322x-dkh.2
> 				load : Base-Bootstrap.v3-dkh.29
> 				load : Bootstrap.v34-dkh.261
> 				load : GemStone-ANSI-Streams-dkh.9
> 				load : GemStone-Indexing-Extensions-dkh.3
> 				load : Squeak.v34-dkh.339
> 				load : Regex-Core-DaleHenrichs.3
> 				load : Regex-Tests-Core-DaleHenrichs.5
> 			atomic load : 0.243 [ConfigurationOfGsMisc]
> 				load : Announcements.v3-dkh.18
> 				load : GemStone-Release-Support-dkh.67
> 			load : Grease-Core
> 			atomic load : 0.243 [ConfigurationOfGsMisc]
> 			atomic load : 0.243 [ConfigurationOfGsMisc]
> 			load : Grease-GemStone-Core
> 			load : Grease-GemStone330-Core
> 			load : Grease-Tests-Core
> 			load : Grease-Tests-GemStone-Core.v32
> 		load : Seaside-Continuation
> 		linear load : baseline [BaselineOfGrease]
> 			atomic load : 0.243 [ConfigurationOfGsMisc]
> 			load : Grease-Core
> 			atomic load : 0.243 [ConfigurationOfGsMisc]
> 			atomic load : 0.243 [ConfigurationOfGsMisc]
> 			load : Grease-GemStone-Core
> 			load : Grease-GemStone330-Core
> 			load : Grease-Tests-Core
> 			load : Grease-Tests-GemStone-Core.v32
> 		load : Seaside-Core
> 		load : Seaside-GemStone320-Core
> 		load : Seaside-GemStone-Core
> 		load : Seaside-GemStone-Basic-Development
> 		load : Seaside-Tests-Core
> 		load : Seaside-Tests-GemStone-Core
> 		load : Seaside-Email
> 		load : Seaside-GemStone-Email
> 		load : Seaside-Canvas
> 		load : Seaside-JSON-Core
> 		load : Seaside-GemStone-JSON-Core
> 		load : Javascript-Core
> 		load : Javascript-GemStone-Core
> 		load : JQuery-Core
> 		load : JQuery-UI
> 		load : JQuery-JSON
> 		load : Seaside-Session
> 		load : Seaside-GemStone-Session
> 		load : Seaside-Component
> 		load : Seaside-Widgets
> 		load : Seaside-GemStone-Tools-Production
> 		load : Seaside-RenderLoop
> 		load : Seaside-Tools-Core
> 		load : Seaside-Tools-Web
> 		load : Seaside-GemStone-Tools-Web
> 		load : Seaside-Flow
> 		load : Seaside-Development
> 		load : Seaside-GemStone-Development
> 		load : Seaside-Examples
> 		load : Seaside-Environment
> 		load : Seaside-GemStone-Environment
> 		load : Seaside-Tests-Functional
> 		load : Seaside-Tests-GemStone-Functional
> 		load : Seaside-Tests-Flow
> 		load : Seaside-Tests-GemStone-Flow
> 		load : Seaside-Welcome
> 		load : Seaside-GemStone-Welcome
> 		load : Seaside-GemStone-Continuation
> 		load : Seaside-Tests-GemStone-Continuation
> 		load : Seaside-GemStone-Flow
> 
> I started off talking about the Monticello load with Monticello meta data ... If you've got a metadataless repository and you've got a projectClass method in the baseline that references MetacelloCypressBaselineProject, then Metacello will ignore the mcz version calculation and load all of the packages from the target repository (which because of git, are all of the proper version). Metacello relies on the fact that Monticello does a package definition comparison before loading which means that only the changed definitions will actually be loaded ... 
> 
> If you don't have a projectClass method in your baseline in a metadataless repository, then Metacello _will_ apply the mcz version rule and because all of the mcz version for packages in a metadataless repository is 1, Metacello will not load anything at all ... the second time you try to load the project in the repository ... 
> 
> Dale
> 




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