Skip to content

Commit

Permalink
Add JVMTI synchronization in JVM_VirtualThreadHideFrames
Browse files Browse the repository at this point in the history 
J9VMThread->threadObject can be modified between
JVM_VirtualThreadHideFrames's first invocation with hide=true and
second invocation with hide=false. Synchronization to prevent JVMTI
operations is acquired between these two invocations. This prevents
JVMTI functions to see an unstable J9VMThread->threadObject.

Related: eclipse-openj9#17865
Related: eclipse-openj9#17869
Related: eclipse-openj9#18370

Co-authored-by: Jack Lu <Jack.S.Lu@ibm.com>
Signed-off-by: Babneet Singh <sbabneet@ca.ibm.com>
  • Loading branch information
@babsingh @fengxue-IS
babsingh and fengxue-IS committed Nov 20, 2023
1 parent 69fbaa8 commit ecdbc7b
Showing 1 changed file with 29 additions and 10 deletions.
39 changes: 29 additions & 10 deletions runtime/j9vm/javanextvmi.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -310,8 +310,6 @@ virtualThreadMountBegin(JNIEnv *env, jobject thread)
{
J9VMThread *currentThread = (J9VMThread *)env;

VM_VMHelpers::virtualThreadHideFrames(currentThread, JNI_TRUE);

j9object_t threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
Assert_SC_true(IS_JAVA_LANG_VIRTUALTHREAD(currentThread, threadObj));

Expand Down Expand Up @@ -351,6 +349,8 @@ virtualThreadMountBegin(JNIEnv *env, jobject thread)
enterVThreadTransitionCritical(currentThread, thread);
threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
}

VM_VMHelpers::virtualThreadHideFrames(currentThread, JNI_TRUE);
}

/* Caller must have VMAccess. */
Expand All @@ -361,8 +361,6 @@ virtualThreadMountEnd(JNIEnv *env, jobject thread)
J9JavaVM *vm = currentThread->javaVM;
j9object_t threadObj = J9_JNI_UNWRAP_REFERENCE(thread);

VM_VMHelpers::virtualThreadHideFrames(currentThread, JNI_FALSE);

Assert_SC_true(IS_JAVA_LANG_VIRTUALTHREAD(currentThread, threadObj));

if (TrcEnabled_Trc_SC_VirtualThread_Info) {
Expand All @@ -377,6 +375,8 @@ virtualThreadMountEnd(JNIEnv *env, jobject thread)
J9VMJDKINTERNALVMCONTINUATION_VMREF(currentThread, continuationObj));
}

VM_VMHelpers::virtualThreadHideFrames(currentThread, JNI_FALSE);

/* Allow thread to be inspected again. */
exitVThreadTransitionCritical(currentThread, threadObj);

Expand Down Expand Up @@ -409,7 +409,6 @@ virtualThreadUnmountBegin(JNIEnv *env, jobject thread)
TRIGGER_J9HOOK_VM_VIRTUAL_THREAD_UNMOUNT(vm->hookInterface, currentThread);

enterVThreadTransitionCritical(currentThread, thread);
VM_VMHelpers::virtualThreadHideFrames(currentThread, JNI_TRUE);

J9InternalVMFunctions *vmFuncs = vm->internalVMFunctions;
j9object_t carrierThreadObject = currentThread->carrierThreadObject;
Expand All @@ -432,6 +431,8 @@ virtualThreadUnmountBegin(JNIEnv *env, jobject thread)
carrierThreadObject = currentThread->carrierThreadObject;
threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
}

VM_VMHelpers::virtualThreadHideFrames(currentThread, JNI_TRUE);
}

/* Caller must have VMAccess. */
Expand All @@ -442,8 +443,6 @@ virtualThreadUnmountEnd(JNIEnv *env, jobject thread)
J9JavaVM *vm = currentThread->javaVM;
J9InternalVMFunctions *vmFuncs = vm->internalVMFunctions;

VM_VMHelpers::virtualThreadHideFrames(currentThread, JNI_FALSE);

j9object_t threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
j9object_t continuationObj = J9VMJAVALANGVIRTUALTHREAD_CONT(currentThread, threadObj);
ContinuationState continuationState = *VM_ContinuationHelpers::getContinuationStateAddress(currentThread, continuationObj);
Expand All @@ -465,6 +464,8 @@ virtualThreadUnmountEnd(JNIEnv *env, jobject thread)
vmFuncs->freeTLS(currentThread, threadObj);
}

VM_VMHelpers::virtualThreadHideFrames(currentThread, JNI_FALSE);

/* Allow thread to be inspected again. */
exitVThreadTransitionCritical(currentThread, threadObj);
}
Expand Down Expand Up @@ -577,13 +578,31 @@ JNIEXPORT void JNICALL
JVM_VirtualThreadHideFrames(JNIEnv *env, jobject vthread, jboolean hide)
{
J9VMThread *currentThread = (J9VMThread *)env;
J9InternalVMFunctions const * const vmFuncs = currentThread->javaVM->internalVMFunctions;

vmFuncs->internalEnterVMFromJNI(currentThread);

j9object_t vThreadObj = currentThread->threadObject;
Assert_SC_true(IS_JAVA_LANG_VIRTUALTHREAD(currentThread, vThreadObj));
/* Do not allow JVMTI operations because J9VMThread->threadObject is modified
* between the first invocation with hide=true and the second invocation with
* hide=false. Otherwise, JVMTI functions will see an unstable
* J9VMThread->threadObject.
*/
bool hiddenFrames = J9_ARE_ALL_BITS_SET(currentThread->privateFlags, J9_PRIVATE_FLAGS_VIRTUAL_THREAD_HIDDEN_FRAMES);
if (hide) {
Assert_SC_true(J9_ARE_NO_BITS_SET(currentThread->privateFlags, J9_PRIVATE_FLAGS_VIRTUAL_THREAD_HIDDEN_FRAMES));
} else {
Assert_SC_true(J9_ARE_ALL_BITS_SET(currentThread->privateFlags, J9_PRIVATE_FLAGS_VIRTUAL_THREAD_HIDDEN_FRAMES));
Assert_SC_true(!hiddenFrames && (vThreadObj == J9_JNI_UNWRAP_REFERENCE(vthread)));
enterVThreadTransitionCritical(currentThread, vthread);
}

VM_VMHelpers::virtualThreadHideFrames(currentThread, hide);

if (!hide) {
Assert_SC_true(hiddenFrames);
exitVThreadTransitionCritical(currentThread, vThreadObj);
}

vmFuncs->internalExitVMToJNI(currentThread);
}
#endif /* JAVA_SPEC_VERSION >= 20 */

Expand Down

0 comments on commit ecdbc7b

Please sign in to comment.