There are 2 places in AdvancedThresholdPolicy::select_task where safepoint can occur:
- AdvancedThresholdPolicy::update_rate
- CompileTaskWrapper::~CompileTaskWrapper for a stale task

AdvancedThresholdPolicy::select_task is called from CompileQueue::get() which holds MethodCompileQueue_lock.

Additional precautions are needed to avoid deadlocks in VM thread, so there's an agreement when entering a safepoint to avoid holding any locks VM thread can use (see [1]).

[1] http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/file/tip/src/share/vm/runtime/thread.cpp#l903