--- a/src/hotspot/share/runtime/interfaceSupport.inline.hpp Tue Feb 05 13:21:59 2019 -0500
+++ b/src/hotspot/share/runtime/interfaceSupport.inline.hpp Tue Feb 05 15:12:13 2019 -0500
@@ -286,6 +286,69 @@
}
};
+// Unlike ThreadBlockInVM, this class is designed to avoid certain deadlock scenarios while making
+// transitions inside class Monitor in cases where we need to block for a safepoint or handshake. It
+// receives an extra argument compared to ThreadBlockInVM, the address of a pointer to the monitor we
+// are trying to acquire. This will be used to access and release the monitor if needed to avoid
+// said deadlocks.
+// It works like ThreadBlockInVM but differs from it in two ways:
+// - When transitioning in (constructor), it checks for safepoints without blocking, i.e., calls
+// back if needed to allow a pending safepoint to continue but does not block in it.
+// - When transitioning back (destructor), if there is a pending safepoint or handshake it releases
+// the monitor that is only partially acquired.
+class ThreadBlockInVMWithDeadlockCheck : public ThreadStateTransition {
+ private:
+ Monitor** _in_flight_monitor_adr;
+
+ void release_monitor() {
+ assert(_in_flight_monitor_adr != NULL, "_in_flight_monitor_adr should have been set on constructor");
+ Monitor* in_flight_monitor = *_in_flight_monitor_adr;
+ if (in_flight_monitor != NULL) {
+ in_flight_monitor->release_for_safepoint();
+ *_in_flight_monitor_adr = NULL;
+ }
+ }
+ public:
+ ThreadBlockInVMWithDeadlockCheck(JavaThread* thread, Monitor** in_flight_monitor_adr)
+ : ThreadStateTransition(thread), _in_flight_monitor_adr(in_flight_monitor_adr) {
+ // Once we are blocked vm expects stack to be walkable
+ thread->frame_anchor()->make_walkable(thread);
+
+ thread->set_thread_state((JavaThreadState)(_thread_in_vm + 1));
+ InterfaceSupport::serialize_thread_state_with_handler(thread);
+
+ SafepointMechanism::callback_if_safepoint(thread);
+
+ thread->set_thread_state(_thread_blocked);
+
+ CHECK_UNHANDLED_OOPS_ONLY(_thread->clear_unhandled_oops();)
+ }
+ ~ThreadBlockInVMWithDeadlockCheck() {
+ // Change to transition state
+ _thread->set_thread_state((JavaThreadState)(_thread_blocked + 1));
+
+ InterfaceSupport::serialize_thread_state_with_handler(_thread);
+
+ if (SafepointMechanism::should_block(_thread)) {
+ release_monitor();
+ SafepointMechanism::callback_if_safepoint(_thread);
+ // The VMThread might have read that we were in a _thread_blocked state
+ // and proceeded to process a handshake for us. If that's the case then
+ // we need to block.
+ // By doing this we are also making the current thread process its own
+ // handshake if there is one pending and the VMThread didn't try to process
+ // it yet. This is more of a side-effect and not really necessary; the
+ // handshake could be processed later on.
+ if (_thread->has_handshake()) {
+ _thread->handshake_process_by_self();
+ }
+ }
+
+ _thread->set_thread_state(_thread_in_vm);
+ CHECK_UNHANDLED_OOPS_ONLY(_thread->clear_unhandled_oops();)
+ }
+};
+
// This special transition class is only used to prevent asynchronous exceptions
// from being installed on vm exit in situations where we can't tolerate them.