7145345: Code cache sweeper must cooperate with safepoints

Summary: Safepoint in the sweeper loop in necessary
Reviewed-by: kvn, never

src/share/vm/runtime/globals.hpp

@@ -3013,7 +3013,7 @@ class CommandLineFlags {
   product(intx, SafepointTimeoutDelay, 10000,                               \
           "Delay in milliseconds for option SafepointTimeout")              \
                                                                             \
-  product(intx, NmethodSweepFraction, 4,                                    \
+  product(intx, NmethodSweepFraction, 16,                                    \
           "Number of invocations of sweeper to cover all nmethods")         \
                                                                             \
   product(intx, NmethodSweepCheckInterval, 5,                               \

src/share/vm/runtime/sweeper.cpp

@@ -266,7 +266,17 @@ void NMethodSweeper::sweep_code_cache() {
 
     // The last invocation iterates until there are no more nmethods
     for (int i = 0; (i < todo || _invocations == 1) && _current != NULL; i++) {
+      if (SafepointSynchronize::is_synchronizing()) { // Safepoint request
+        if (PrintMethodFlushing && Verbose) {
+          tty->print_cr("### Sweep at %d out of %d, invocation: %d, yielding to safepoint", _seen, CodeCache::nof_nmethods(), _invocations);
+        }
+        MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 
+        assert(Thread::current()->is_Java_thread(), "should be java thread");
+        JavaThread* thread = (JavaThread*)Thread::current();
+        ThreadBlockInVM tbivm(thread);
+        thread->java_suspend_self();
+      }
       // Since we will give up the CodeCache_lock, always skip ahead
       // to the next nmethod.  Other blobs can be deleted by other
       // threads but nmethods are only reclaimed by the sweeper.