[foreign] RFR 8226250: Calling callback from different native threads causes a VM crash

[Henry Jen]

Looks reasonable to me, a nit though,

JavaVM_ *vm = (JavaVM *)(&main_vm);

This line really bothers me, the cast and target type is different, although it’s correct under cpp.
I would suggest make sure we use JavaVM all the way after cast with something like following for all 4 files.

Cheers,
Henry



diff -r 3b046562fe37 src/hotspot/cpu/x86/universalUpcallHandler_x86.cpp
--- a/src/hotspot/cpu/x86/universalUpcallHandler_x86.cpp        Mon Jun 17 12:44:44 2019 -0700
+++ b/src/hotspot/cpu/x86/universalUpcallHandler_x86.cpp        Mon Jun 17 12:57:23 2019 -0700
@@ -189,8 +189,8 @@

   JavaThread* thread = JavaThread::current();
   if (thread == NULL) {
-    JavaVM_ *vm = (JavaVM *)(&main_vm);
-    vm -> functions -> AttachCurrentThreadAsDaemon(vm, &p_env, NULL);
+    JavaVM *vm = (JavaVM *)(&main_vm);
+    vm->AttachCurrentThreadAsDaemon(&p_env, NULL);
     thread = JavaThread::current();
   }


> On Jun 17, 2019, at 10:14 AM, Maurizio Cimadamore <maurizio.cimadamore at oracle.com> wrote:
> 
> Hi,
> Under JNI, it is user responsibility to attach native threads to the VM using attachCurrentThread/detachCurrentThread.
> 
> Panama doesn't do this and, as a result, if native code creates a new thread and uses it to call a Java callback, an hard crash occurs.
> 
> This patch adds a call to AttachCurrentThreadAsDaemon before calling the Java callback, only if the native thread has no associated Java thread.
> 
> The AttachCurrentThreadAsDaemon allows the VM to be shutdown w/o waiting for native threads to complete, which is, I think the semantics we want.
> 
> We don't call the dual detach method for two reasons:
> 
> * re-attaching the same thread over and over can be expensive
> 
> * calling detach after the callback means that we'd lose some register values, so we would additional save/restore
> 
> Overall, it seems like the 'leak' of JavaThread is not worth the extra complexity?
> 
> Webrev:
> 
> http://cr.openjdk.java.net/~mcimadamore/panama/8226250_v2/
> 
> Maurizio
>