Note that my diagram formatting is very hard to read in the default formatting on this mailing list. If you view my email in 'raw source' then it is easier to understand!
On 2024/02/06 10:40:14 Joseph Leonard wrote: > Hi all, > > It would be great to get any thoughts on whether the following is a defect: > > > Issue details: > tl;dr > > Maven can resolve dependencies either from: > > * an external repo > * a class directory of a module being built within the reactor > * a packaged jar of a module being built within the reactor > > If you run a concurrent multi-module build it is possible to get a race > condition whereby the build of module Foo may resolve module Bar from either > of the three resolution channels. This inconsistency can result in the Maven > war plugin sometimes failing to build a functional war file. I would expect a > consistent resolution would always take place. > > Full details > Scenario > > Consider you have a repo with the following structure: > > App > > / \ > > / \ > > (compile scope) (test scope) > > / \ > > \/_ _\/ > > ModuleA TestSupportModule1 > > / > > / > > (compile scope) > > / > > \/_ > > ModuleB > > / > > / > > (test scope) > > / > > \/_ > > TestSupportModule2 > > If you were to make a src code change to the following test support modules: > > * TestSupportModule1 > * TestSupportModule2 > > Then the minimum number of modules we need to build to verify the change set > is OK is: > > * TestSupportModule1 > * TestSupportModule2 > * ModuleB > * App > > i.e. there is no requirement to build ModuleA because we know that none of > the src code changes could impact the classpaths used in its maven build. > > We know that despite 'App' depending (transitively) on ModuleB there is no > need for the 'App' build to wait for ModuleB to complete its build because > the src code change to TestSupportModule2 will not impact any of the > classpaths used in the App maven build. Therefore to get the most efficient > build possible we ideally would invoke Maven to run with 2 threads and with > instruction to build two distinct 'dependency graphs': > > * TestSupportModule1 followed by ModuleB > * TestSupportModule1 followed by App > > The following Maven command achieves exactly what we want because the reactor > build order is based only on the direct (i.e. non-transitive) dependencies of > the modules provided to the reactor in the build command. Therefore the > absence of ModuleA results in two distinct 'dependency graphs': > > mvn clean verify -pl TestSupportModule1,TestSupportModule2,ModuleB,App -T 2 > > Note: In reality the code base I maintain has a very large monobuild with > 100s of modules and this type of build optimisation makes a significant > difference to the speed of our monobuild (we use > https://github.com/gitflow-incremental-builder/gitflow-incremental-builder to > automate the logic of determining which modules to include in the reactor > based on our change set). > > Issue > > We have encountered an issue in the above scenario because the 'App' build > has a race condition with the ModuleB build which will result in one of the > following three outcomes: > > * If the 'App' build starts before the ModuleB build has compiled its src > classes then the 'App' build will resolve ModuleB from the external repo > (i.e. equivalent to ModuleB not being in the reactor at all) > * If the 'App' build starts after ModuleB has compiled its src classes > but before it has packaged these classes into a jar then the 'App' build will > resolve ModuleB's target/classes directory > * If the 'App' build starts after ModuleB has packaged its jar file then > the 'App' build will resolve ModuleB's target/ModuleB.jar file. > > In many scenarios this dependency resolution inconsistency doesn't represent > a challenge. However, it does cause an issue in our case because the 'App' > POM has its Maven packaging stanza configured to war and in the scenario > where ModuleB's target/classes directory is resolved by the 'App' then this > results in the resultant 'App' war file being packaged with a completely > empty ModuleB.jar file. > > Proposed solution > > Ideally we would like the Maven reactor to retain isolation between the two > distinct 'dependency graphs' it constructs at instantiation throughout the > entire Maven build. This would mean, in the simple example above, that the > 'App' would always resolves ModuleB from the external repo (regardless of > whether the reactor has built ModuleB or not in a separate 'dependency graph' > in the reactor). > > > > Joseph Leonard > Manager > > Alfa > ________________________________ > e: joseph.leon...@alfasystems.com | w: > alfasystems.com<https://www.alfasystems.com> > t: +44 (0)20 7588 1800 | Moor Place, 1 Fore Street Avenue, London, EC2Y 9DT, > GB > ________________________________ > > The contents of this communication are not intended to be binding or > constitute any form of offer or acceptance or give rise to any legal > obligations on behalf of the sender or Alfa. The views or opinions expressed > represent those of the author and not necessarily those of Alfa. This email > and any attachments are strictly confidential and are intended solely for use > by the individual or entity to whom it is addressed. If you are not the > addressee (or responsible for delivery of the message to the addressee) you > may not copy, forward, disclose or use any part of the message or its > attachments. At present the integrity of email across the internet cannot be > guaranteed and messages sent via this medium are potentially at risk. All > liability is excluded to the extent permitted by law for any claims arising > as a result of the use of this medium to transmit information by or to Alfa > or its affiliates. > > Alfa Financial Software Ltd > Reg. in England No: 0248 2325 >
