8374449: Shenandoah: Leaf locks used by Shenandoah need lower ranks

Reviewed-by: ysr

src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp

@@ -44,7 +44,7 @@ ShenandoahControlThread::ShenandoahControlThread() :
   ShenandoahController(),
   _requested_gc_cause(GCCause::_no_gc),
   _degen_point(ShenandoahGC::_degenerated_outside_cycle),
-  _control_lock(Mutex::nosafepoint - 2, "ShenandoahGCRequest_lock", true) {
+  _control_lock(CONTROL_LOCK_RANK, "ShenandoahControl_lock", true) {
   set_name("Shenandoah Control Thread");
   create_and_start();
 }

src/hotspot/share/gc/shenandoah/shenandoahController.hpp

@@ -42,6 +42,9 @@ private:
   shenandoah_padding(1);
 
 protected:
+  const Mutex::Rank WAITERS_LOCK_RANK = Mutex::safepoint - 5;
+  const Mutex::Rank CONTROL_LOCK_RANK = Mutex::nosafepoint - 2;
+
   // While we could have a single lock for these, it may risk unblocking
   // GC waiters when alloc failure GC cycle finishes. We want instead
   // to make complete explicit cycle for demanding customers.
@@ -54,8 +57,8 @@ protected:
 public:
   ShenandoahController():
     _gc_id(0),
-    _alloc_failure_waiters_lock(Mutex::safepoint-2, "ShenandoahAllocFailureGC_lock", true),
-    _gc_waiters_lock(Mutex::safepoint-2, "ShenandoahRequestedGC_lock", true)
+    _alloc_failure_waiters_lock(WAITERS_LOCK_RANK, "ShenandoahAllocFailureWaiters_lock", true),
+    _gc_waiters_lock(WAITERS_LOCK_RANK, "ShenandoahGCWaiters_lock", true)
   { }
 
   // Request a collection cycle. This handles "explicit" gc requests

src/hotspot/share/gc/shenandoah/shenandoahGenerationalControlThread.cpp

@@ -47,7 +47,7 @@
 #include "utilities/events.hpp"
 
 ShenandoahGenerationalControlThread::ShenandoahGenerationalControlThread() :
-  _control_lock(Mutex::nosafepoint - 2, "ShenandoahGCRequest_lock", true),
+  _control_lock(CONTROL_LOCK_RANK, "ShenandoahGCRequest_lock", true),
   _requested_gc_cause(GCCause::_no_gc),
   _requested_generation(nullptr),
   _gc_mode(none),