[FELIX-5615] Global lock in BaseMethod.NotResolved::resolve method can cause deadlock

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: scr-2.0.10
• Component/s: Declarative Services (SCR)
• External issue URL: https://bugs.eclipse.org/bugs/show_bug.cgi?id=515215
• Assignee: Tom Watson
• Reporter: Tom Watson
• Created: 13/Apr/17 20:08
• Updated: 28/Apr/17 08:40
• Resolved: 20/Apr/17 13:32

Description

See eclipse bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=515215

org.apache.felix.scr.impl.inject.BaseMethod.NotResolved has a single instance which is held by the static field NotResolved.INSTANCE

This means that the synchronized method NotResolved::resolve holds the global lock on this NotResolved.INSTANCE object. It is unclear why this complete method needs to be synchronized. But is is also unclear why it has to be a global lock also. Is this by design? or a consequence of some refactoring that made this method act on a global lock?

This is causing issues because while calling BaseMethod::findMethod reflection is done which can then trigger additional class loads. These can then result in lazy activation to be triggered. There is a whole set of deadlock situations that could happen during lazy activation while this global lock is being held.

I have not studied the code in detail, but it appears BaseMethod:findMethod is stateless and it is unclear why we need to hold a lock between calls to BaseMethod::findMethod and BaseMethod::setMethod (let alone a global lock).