src/hotspot/share/gc/shenandoah/shenandoahRootProcessor.inline.hpp

rev 59533 : 8246097: Shenandoah: limit parallelism in CLDG root handling
Reviewed-by: XXX

@@ -120,11 +120,12 @@
   _jni_handle_roots.oops_do(cl, worker_id);
   _vm_global_roots.oops_do(cl, worker_id);
 }
 
 template <bool CONCURRENT, bool SINGLE_THREADED>
-ShenandoahClassLoaderDataRoots<CONCURRENT, SINGLE_THREADED>::ShenandoahClassLoaderDataRoots(ShenandoahPhaseTimings::Phase phase) :
+ShenandoahClassLoaderDataRoots<CONCURRENT, SINGLE_THREADED>::ShenandoahClassLoaderDataRoots(ShenandoahPhaseTimings::Phase phase, uint n_workers) :
+  _semaphore(worker_count(n_workers)),
   _phase(phase) {
   if (!SINGLE_THREADED) {
     ClassLoaderDataGraph::clear_claimed_marks();
   }
   if (CONCURRENT) {

@@ -144,25 +145,27 @@
 void ShenandoahClassLoaderDataRoots<CONCURRENT, SINGLE_THREADED>::always_strong_cld_do(CLDClosure* clds, uint worker_id) {
   if (SINGLE_THREADED) {
     assert(SafepointSynchronize::is_at_safepoint(), "Must be at a safepoint");
     assert(Thread::current()->is_VM_thread(), "Single threaded CLDG iteration can only be done by VM thread");
     ClassLoaderDataGraph::always_strong_cld_do(clds);
-  } else {
+  } else if (_semaphore.try_acquire()) {
     ShenandoahWorkerTimingsTracker timer(_phase, ShenandoahPhaseTimings::CLDGRoots, worker_id);
     ClassLoaderDataGraph::always_strong_cld_do(clds);
+    _semaphore.claim_all();
   }
 }
 
 template <bool CONCURRENT, bool SINGLE_THREADED>
 void ShenandoahClassLoaderDataRoots<CONCURRENT, SINGLE_THREADED>::cld_do(CLDClosure* clds, uint worker_id) {
   if (SINGLE_THREADED) {
     assert(SafepointSynchronize::is_at_safepoint(), "Must be at a safepoint");
     assert(Thread::current()->is_VM_thread(), "Single threaded CLDG iteration can only be done by VM thread");
     ClassLoaderDataGraph::cld_do(clds);
-  } else {
+  } else if (_semaphore.try_acquire()) {
     ShenandoahWorkerTimingsTracker timer(_phase, ShenandoahPhaseTimings::CLDGRoots, worker_id);
     ClassLoaderDataGraph::cld_do(clds);
+    _semaphore.claim_all();
   }
 }
 
 class ShenandoahParallelOopsDoThreadClosure : public ThreadClosure {
 private: