8275226: Shenandoah: Relax memory constraint for worker claiming tasks/ranges

Reviewed-by: shade

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

@@ -87,7 +87,7 @@ void ShenandoahParallelCodeHeapIterator::parallel_blobs_do(CodeBlobClosure* f) {
     int current = count++;
     if ((current & stride_mask) == 0) {
       process_block = (current >= _claimed_idx) &&
-                      (Atomic::cmpxchg(&_claimed_idx, current, current + stride) == current);
+                      (Atomic::cmpxchg(&_claimed_idx, current, current + stride, memory_order_relaxed) == current);
     }
     if (process_block) {
       if (cb->is_alive()) {

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

@@ -493,7 +493,7 @@ void ShenandoahNMethodTableSnapshot::parallel_blobs_do(CodeBlobClosure *f) {
 
   size_t max = (size_t)_limit;
   while (_claimed < max) {
-    size_t cur = Atomic::fetch_and_add(&_claimed, stride);
+    size_t cur = Atomic::fetch_and_add(&_claimed, stride, memory_order_relaxed);
     size_t start = cur;
     size_t end = MIN2(cur + stride, max);
     if (start >= max) break;
@@ -520,7 +520,7 @@ void ShenandoahNMethodTableSnapshot::concurrent_nmethods_do(NMethodClosure* cl)
   ShenandoahNMethod** list = _list->list();
   size_t max = (size_t)_limit;
   while (_claimed < max) {
-    size_t cur = Atomic::fetch_and_add(&_claimed, stride);
+    size_t cur = Atomic::fetch_and_add(&_claimed, stride, memory_order_relaxed);
     size_t start = cur;
     size_t end = MIN2(cur + stride, max);
     if (start >= max) break;

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

@@ -453,14 +453,14 @@ void ShenandoahReferenceProcessor::process_references(ShenandoahRefProcThreadLoc
 void ShenandoahReferenceProcessor::work() {
   // Process discovered references
   uint max_workers = ShenandoahHeap::heap()->max_workers();
-  uint worker_id = Atomic::add(&_iterate_discovered_list_id, 1U) - 1;
+  uint worker_id = Atomic::add(&_iterate_discovered_list_id, 1U, memory_order_relaxed) - 1;
   while (worker_id < max_workers) {
     if (UseCompressedOops) {
       process_references<narrowOop>(_ref_proc_thread_locals[worker_id], worker_id);
     } else {
       process_references<oop>(_ref_proc_thread_locals[worker_id], worker_id);
     }
-    worker_id = Atomic::add(&_iterate_discovered_list_id, 1U) - 1;
+    worker_id = Atomic::add(&_iterate_discovered_list_id, 1U, memory_order_relaxed) - 1;
   }
 }
 

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

@@ -337,7 +337,7 @@ T* ParallelClaimableQueueSet<T, F>::claim_next() {
     return NULL;
   }
 
-  jint index = Atomic::add(&_claimed_index, 1);
+  jint index = Atomic::add(&_claimed_index, 1, memory_order_relaxed);
 
   if (index <= size) {
     return GenericTaskQueueSet<T, F>::queue((uint)index - 1);