8324983: race in CompileBroker::possibly_add_compiler_threads

Reviewed-by: kvn, dholmes, dnsimon

src/hotspot/share/compiler/compileBroker.cpp

@@ -841,8 +841,15 @@ void DeoptimizeObjectsALotThread::deoptimize_objects_alot_loop_all() {
 
 
 JavaThread* CompileBroker::make_thread(ThreadType type, jobject thread_handle, CompileQueue* queue, AbstractCompiler* comp, JavaThread* THREAD) {
-  JavaThread* new_thread = nullptr;
+  Handle thread_oop(THREAD, JNIHandles::resolve_non_null(thread_handle));
 
+  if (java_lang_Thread::thread(thread_oop()) != nullptr) {
+    assert(type == compiler_t, "should only happen with reused compiler threads");
+    // The compiler thread hasn't actually exited yet so don't try to reuse it
+    return nullptr;
+  }
+
+  JavaThread* new_thread = nullptr;
   switch (type) {
     case compiler_t:
       assert(comp != nullptr, "Compiler instance missing.");
@@ -871,7 +878,6 @@ JavaThread* CompileBroker::make_thread(ThreadType type, jobject thread_handle, C
   // JavaThread due to lack of resources. We will handle that failure below.
   // Also check new_thread so that static analysis is happy.
   if (new_thread != nullptr && new_thread->osthread() != nullptr) {
-    Handle thread_oop(THREAD, JNIHandles::resolve_non_null(thread_handle));
 
     if (type == compiler_t) {
       CompilerThread::cast(new_thread)->set_compiler(comp);

src/hotspot/share/runtime/javaThread.cpp

@@ -745,6 +745,7 @@ static void ensure_join(JavaThread* thread) {
   // Clear the native thread instance - this makes isAlive return false and allows the join()
   // to complete once we've done the notify_all below. Needs a release() to obey Java Memory Model
   // requirements.
+  assert(java_lang_Thread::thread(threadObj()) == thread, "must be alive");
   java_lang_Thread::release_set_thread(threadObj(), nullptr);
   lock.notify_all(thread);
   // Ignore pending exception, since we are exiting anyway
@@ -2155,6 +2156,8 @@ void JavaThread::start_internal_daemon(JavaThread* current, JavaThread* target,
   // on a ThreadsList. We don't want to wait for the release when the
   // Theads_lock is dropped when the 'mu' destructor is run since the
   // JavaThread* is already visible to JVM/TI via the ThreadsList.
+
+  assert(java_lang_Thread::thread(thread_oop()) == nullptr, "must not be alive");
   java_lang_Thread::release_set_thread(thread_oop(), target); // isAlive == true now
   Thread::start(target);
 }