6822370: ReentrantReadWriteLock: threads hung when there are no threads...

6822370: ReentrantReadWriteLock: threads hung when there are no threads holding onto the lock (Netra x4450)
Summary: This day one bug is caused by missing memory barriers in various Parker::park() paths that can result in lost wakeups and hangs.
Reviewed-by: dice, acorn

src/os/linux/vm/os_linux.cpp

@@ -4683,6 +4683,7 @@ void Parker::park(bool isAbsolute, jlong time) {
   // Return immediately if a permit is available.
   if (_counter > 0) {
       _counter = 0 ;
+      OrderAccess::fence();
       return ;
   }
 
@@ -4725,6 +4726,7 @@ void Parker::park(bool isAbsolute, jlong time) {
     _counter = 0;
     status = pthread_mutex_unlock(_mutex);
     assert (status == 0, "invariant") ;
+    OrderAccess::fence();
     return;
   }
 
@@ -4765,6 +4767,7 @@ void Parker::park(bool isAbsolute, jlong time) {
     jt->java_suspend_self();
   }
 
+  OrderAccess::fence();
 }
 
 void Parker::unpark() {

src/os/solaris/vm/os_solaris.cpp

@@ -5803,6 +5803,7 @@ void Parker::park(bool isAbsolute, jlong time) {
   // Return immediately if a permit is available.
   if (_counter > 0) {
       _counter = 0 ;
+      OrderAccess::fence();
       return ;
   }
 
@@ -5846,6 +5847,7 @@ void Parker::park(bool isAbsolute, jlong time) {
     _counter = 0;
     status = os::Solaris::mutex_unlock(_mutex);
     assert (status == 0, "invariant") ;
+    OrderAccess::fence();
     return;
   }
 
@@ -5892,6 +5894,7 @@ void Parker::park(bool isAbsolute, jlong time) {
     jt->java_suspend_self();
   }
 
+  OrderAccess::fence();
 }
 
 void Parker::unpark() {