JDK-8242440 added support for a JIT compiler to be notified when a CompilerThread has an empty compilation queue. It's possible for a specific compiler implementation of AbstractCompiler::on_empty_queue to temporarily release the MethodCompileQueue_lock (e.g. [1]). This means a non-CompilerThread has a chance to enqueue a new compilation task. As such, the CompilerThread should check for this after calling AbstractCompiler::on_empty_queue.

[1] https://github.com/openjdk/jdk/blob/357b1b18c20233f16fba872b79237e9459f5ba43/src/hotspot/share/jvmci/jvmciCompiler.cpp#L174