[BUG] infinite loop in restxq in exist 6.4.0 with circular dependency

[line-o]

Describe the bug

A XAR with modules that have circular dependencies

• module A imports module B
• module B imports module A

can be installed.
Deinstalling this package and reinstalling this will lead to an infinite loop in hot-code that cannot be aborted.
In my testing this could lead to database corruption!

restxq.log will be full of lines similar to

2026-01-15 15:35:03,471 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/a.xqm' has been added to the database, re-examining '/db/apps/my-app/b.xqm'... 
2026-01-15 15:35:04,311 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/b.xqm' has been added to the database, re-examining '/db/apps/my-app/a.xqm'... 
2026-01-15 15:35:05,097 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/a.xqm' has been added to the database, re-examining '/db/apps/my-app/b.xqm'... 
2026-01-15 15:35:05,939 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/b.xqm' has been added to the database, re-examining '/db/apps/my-app/a.xqm'... 
2026-01-15 15:35:06,751 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/a.xqm' has been added to the database, re-examining '/db/apps/my-app/b.xqm'... 
2026-01-15 15:35:07,586 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/b.xqm' has been added to the database, re-examining '/db/apps/my-app/a.xqm'... 
2026-01-15 15:35:08,405 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/a.xqm' has been added to the database, re-examining '/db/apps/my-app/b.xqm'... 
2026-01-15 15:35:09,259 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/b.xqm' has been added to the database, re-examining '/db/apps/my-app/a.xqm'... 
2026-01-15 15:35:10,102 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/a.xqm' has been added to the database, re-examining '/db/apps/my-app/b.xqm'... 
2026-01-15 15:35:10,982 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/b.xqm' has been added to the database, re-examining '/db/apps/my-app/a.xqm'... 
2026-01-15 15:35:11,813 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/a.xqm' has been added to the database, re-examining '/db/apps/my-app/b.xqm'... 
2026-01-15 15:35:12,695 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/b.xqm' has been added to the database, re-examining '/db/apps/my-app/a.xqm'... 
2026-01-15 15:35:13,529 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/a.xqm' has been added to the database, re-examining '/db/apps/my-app/b.xqm'... 
2026-01-15 15:35:14,398 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/b.xqm' has been added to the database, re-examining '/db/apps/my-app/a.xqm'... 
2026-01-15 15:35:15,241 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/a.xqm' has been added to the database, re-examining '/db/apps/my-app/b.xqm'... 
2026-01-15 15:35:16,125 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/b.xqm' has been added to the database, re-examining '/db/apps/my-app/a.xqm'... 
2026-01-15 15:35:16,955 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/a.xqm' has been added to the database, re-examining '/db/apps/my-app/b.xqm'... 
2026-01-15 15:35:17,858 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/b.xqm' has been added to the database, re-examining '/db/apps/my-app/a.xqm'... 
2026-01-15 15:35:18,700 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/a.xqm' has been added to the database, re-examining '/db/apps/my-app/b.xqm'... 
2026-01-15 15:35:19,587 [qtp394019287-33] INFO  (ExistXqueryRegistry.java [reexamineModulesWithResolvedDependencies]:321) - Missing dependency '/db/apps/my-app/b.xqm' has been added to the database, re-examining '/db/apps/my-app/a.xqm'... 

Important findings:

1. There are restxq handlers defined in module C which itself depends on module A
2. The routes annotated in module C are not registered after installation of the package. They had to be re-registered by saving module C in eXide

Expected behavior

1. XAR packages with restxq annotations to be immediately available after installation.
2. restxq routes to be de-registered reliably after XAR package removal
3. XAR packages with circular dependencies to not create an infinite loop on re-installation.

To Reproduce

1. Install xar package with a module with restxq annotations that depends on a module with a circular dependency
2. deinstall package
3. re-install package
4. database rendered unusable as the infinite loop blocks the entire instance

Context (please always complete the following information)

• Build: eXist-6.4.0 (2e41828)
• Java: 1.8.0_452 (Temurin)
• OS: Linux 6.12.54-linuxkit (aarch64)

Additional context

• How is eXist-db installed? Docker
• Any custom changes in e.g. conf.xml? none

[adamretter]

@line-o I fixed this 2+ years ago now in eXist-db 7.x.x - see: #4996