Environment

• jruby 9.1.10.0 (2.3.3) 2017-05-25 b09c48a OpenJDK 64-Bit Server VM 25.141-b16 on 1.8.0_141-b16 +jit [linux-x86_64]
• Linux localhost.localdomain 4.12.5-300.fc26.x86_64 break script engine #1 SMP Mon Aug 7 15:27:25 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

Expected Behavior

• A warning should be emitted, but the overload selection should be stable, e.g. first of all equally good matches.

Actual Behavior

• Different overloads are chosen each time.

Test case

java_import 'java.util.concurrent.Executors'

service = Executors.newFixedThreadPool(1)
future = service.submit(->() { return 42; })
puts "result: '#{future.get}'"
service.shutdown

jruby test.rb
test.rb:4: warning: ambiguous Java methods found, using submit(java.lang.Runnable)
jruby test.rb
test.rb:4: warning: ambiguous Java methods found, using submit(java.util.concurrent.Callable)

Just a guess, this seems like it depends on some unordered data structure, so using a sorted one or sorting overloads before resolution would fix the issue.

Workaround

Use java_send to manually pick the overload.

java_import 'java.util.concurrent.Callable'
future = service.java_send :submit, [Callable], ->() { return 42; }