Hi Tamás, Yeah, this was unexpected to me initially as well. From what I can tell the Maven reactor only considers direct dependencies (i.e. not transitive dependencies) between the modules in the reactor when working out the build graph. For example if you have a simple linear dependency chain of: One --> Two --> Three --> Four --> Five Then invoking “mvn clean verify -pl One,Two,Four,Five -T 2 will result in two ‘graphs’ being built in parallel ([One,Two] and [Four,Five]). I assume this is as designed because it actually offers quite powerful functionality to improve the parallelism in your build. An example of where this is legit is when:
* “Four” has a test scope dependency on “Five” * “One” has a test scoped dependency on “Two” If you made a src code change to “Five” and “Two” then it would be safe to build [One,Two] and [Four,Five] in parallel because you know the changes within these graphs cannot impact each other. Joe On 2024/02/06 21:37:42 Tamás Cservenák wrote: > 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. 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 > > >
