How to identify / get automated hints with cyclic object initialization causing deadlocks in Scala?

Question

The following code runs into future timeouts (in Scala 2.x and Dotty, -Xcheckinit or -Ycheck-init does not help here) because of cyclic object initialization. In complex project

Answer 1

In general, the compiler and JVM will not help you avoid this.

The best you can do to address this is delay evaluation of the cycle by, for instance:

• using lazy val
• using def

Note that either results in some overhead relative to a simple val. I haven't done experiments, but I'd suspect that lazy val (incurring the expense of some synchronization) is better for a case like

lazy val all = Set(Left, Right)

to limit allocations of redundant objects, and that def is better for a case like

def basePath = Base.LeftElement

since that's pretty likely to be inlined by JIT.

See also: How to diagnose or detect deadlocks in static initializers