8282200: ShouldNotReachHere() reached by AsyncGetCallTrace after JDK-…

…8280422

Reviewed-by: dholmes, mdoerr, kevinw

src/hotspot/share/prims/forte.cpp

@@ -562,12 +562,11 @@ static void forte_fill_call_trace_given_top(JavaThread* thd,
 extern "C" {
 JNIEXPORT
 void AsyncGetCallTrace(ASGCT_CallTrace *trace, jint depth, void* ucontext) {
+
   JavaThread* thread;
 
   if (trace->env_id == NULL ||
-    (thread = JavaThread::thread_from_jni_environment(trace->env_id)) == NULL ||
-    thread->is_exiting()) {
-
+      (thread = JavaThread::thread_from_jni_environment(trace->env_id))->is_exiting()) {
     // bad env_id, thread has exited or thread is exiting
     trace->num_frames = ticks_thread_exit; // -8
     return;

src/hotspot/share/runtime/thread.hpp

@@ -1323,14 +1323,15 @@ class JavaThread: public Thread {
   // external JNI entry points where the JNIEnv is passed into the VM.
   static JavaThread* thread_from_jni_environment(JNIEnv* env) {
     JavaThread* current = (JavaThread*)((intptr_t)env - in_bytes(jni_environment_offset()));
-    // We can't get here in a thread that has completed its execution and so
-    // "is_terminated", but a thread is also considered terminated if the VM
+    // We can't normally get here in a thread that has completed its
+    // execution and so "is_terminated", except when the call is from
+    // AsyncGetCallTrace, which can be triggered by a signal at any point in
+    // a thread's lifecycle. A thread is also considered terminated if the VM
     // has exited, so we have to check this and block in case this is a daemon
     // thread returning to the VM (the JNI DirectBuffer entry points rely on
     // this).
     if (current->is_terminated()) {
       current->block_if_vm_exited();
-      ShouldNotReachHere();
     }
     return current;
   }