Howdy, To me this looks like Maven is not aware that the App depends on ModuleB... Are they "plain dependency" linked? Or what kind of dependency we talk about here? In short: why would App start while ModuleB (upstream dep) is not done? Something is fishy here.
T On Tue, Feb 6, 2024 at 11:40 AM Joseph Leonard < joseph.leon...@alfasystems.com> 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. 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