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Spin during VirtualThread MountBegin and UnmountBegin #18439

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Nov 13, 2023
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Spin during VirtualThread MountBegin and UnmountBegin #18439

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63 changes: 45 additions & 18 deletions runtime/j9vm/javanextvmi.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,8 @@ extern "C" {

#if JAVA_SPEC_VERSION >= 19
extern J9JavaVM *BFUjavaVM;

extern IDATA (*f_threadSleep)(I_64 millis);
#endif /* JAVA_SPEC_VERSION >= 19 */

/* Define for debug
Expand Down Expand Up @@ -328,6 +330,27 @@ virtualThreadMountBegin(JNIEnv *env, jobject thread)
}

enterVThreadTransitionCritical(currentThread, thread);

/* Virtual thread is being mounted but it has been suspended. Spin until the
* virtual thread is resumed. The virtual thread should not be mounted until
* it is resumed.
*/
J9JavaVM *vm = currentThread->javaVM;
J9InternalVMFunctions *vmFuncs = vm->internalVMFunctions;
threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
while (0 != J9OBJECT_U32_LOAD(currentThread, threadObj, vm->isSuspendedInternalOffset)) {
exitVThreadTransitionCritical(currentThread, threadObj);
vmFuncs->internalReleaseVMAccess(currentThread);
/* Spin is used instead of the halt flag; otherwise, the carrier thread will
* show as suspended.
*
* TODO: Dynamically increase the sleep time to a bounded maximum.
*/
f_threadSleep(10);
vmFuncs->internalAcquireVMAccess(currentThread);
enterVThreadTransitionCritical(currentThread, thread);
threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
}
}

/* Caller must have VMAccess. */
Expand All @@ -354,15 +377,6 @@ virtualThreadMountEnd(JNIEnv *env, jobject thread)
J9VMJDKINTERNALVMCONTINUATION_VMREF(currentThread, continuationObj));
}

/* Virtual thread is being mounted but it has been suspended. Thus,
* set J9_PUBLIC_FLAGS_HALT_THREAD_JAVA_SUSPEND flag. At this
* point, virtual thread object is stored in targetThread->threadObject.
*/
if (0 != J9OBJECT_U32_LOAD(currentThread, threadObj, vm->isSuspendedInternalOffset)) {
Assert_SC_true(threadObj == currentThread->threadObject);
vm->internalVMFunctions->setHaltFlag(currentThread, J9_PUBLIC_FLAGS_HALT_THREAD_JAVA_SUSPEND);
}

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

Expand Down Expand Up @@ -396,6 +410,28 @@ virtualThreadUnmountBegin(JNIEnv *env, jobject thread)

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

J9InternalVMFunctions *vmFuncs = vm->internalVMFunctions;
j9object_t carrierThreadObject = currentThread->carrierThreadObject;
threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
/* Virtual thread is being umounted. If its carrier thread is suspended, spin until
* the carrier thread is resumed. The carrier thread should not be mounted until it
* is resumed.
*/
while (0 != J9OBJECT_U32_LOAD(currentThread, carrierThreadObject, vm->isSuspendedInternalOffset)) {
exitVThreadTransitionCritical(currentThread, threadObj);
vmFuncs->internalReleaseVMAccess(currentThread);
/* Spin is used instead of the halt flag; otherwise, the virtual thread will
* show as suspended.
*
* TODO: Dynamically increase the sleep time to a bounded maximum.
*/
f_threadSleep(10);
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vmFuncs->internalAcquireVMAccess(currentThread);
enterVThreadTransitionCritical(currentThread, thread);
carrierThreadObject = currentThread->carrierThreadObject;
threadObj = J9_JNI_UNWRAP_REFERENCE(thread);
}
}

/* Caller must have VMAccess. */
Expand Down Expand Up @@ -429,15 +465,6 @@ virtualThreadUnmountEnd(JNIEnv *env, jobject thread)
vmFuncs->freeTLS(currentThread, threadObj);
}

j9object_t carrierThreadObject = currentThread->carrierThreadObject;
/* The J9_PUBLIC_FLAGS_HALT_THREAD_JAVA_SUSPEND will be set for the virtual
* thread's carrier thread if it was suspended while the virtual thread was mounted.
*/
if (0 != J9OBJECT_U32_LOAD(currentThread, carrierThreadObject, vm->isSuspendedInternalOffset)) {
Assert_SC_true((currentThread->threadObject == carrierThreadObject) && (NULL == currentThread->currentContinuation));
vmFuncs->setHaltFlag(currentThread, J9_PUBLIC_FLAGS_HALT_THREAD_JAVA_SUSPEND);
}

/* Allow thread to be inspected again. */
exitVThreadTransitionCritical(currentThread, threadObj);
}
Expand Down
8 changes: 6 additions & 2 deletions runtime/j9vm/jvm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -212,6 +212,7 @@ typedef IDATA (*MonitorDestroy)(omrthread_monitor_t monitor);
typedef IDATA (* ThreadLibControl)(const char * key, UDATA value);
typedef IDATA (*SetCategory)(omrthread_t thread, UDATA category, UDATA type);
typedef IDATA (*LibEnableCPUMonitor)(omrthread_t thread);
typedef IDATA (*ThreadSleep)(I_64 millis);

typedef I_32 (*PortInitLibrary)(J9PortLibrary *portLib, J9PortLibraryVersion *version, UDATA size);
typedef UDATA (*PortGetSize)(struct J9PortLibraryVersion *version);
Expand Down Expand Up @@ -260,6 +261,7 @@ static pNewStringPlatform globalNewStringPlatform;
static p_a2e_vsprintf global_a2e_vsprintf;
#endif

ThreadSleep f_threadSleep;
static ThreadGlobal f_threadGlobal;
static ThreadAttachEx f_threadAttachEx;
static ThreadDetach f_threadDetach;
Expand Down Expand Up @@ -1015,8 +1017,9 @@ preloadLibraries(void)
f_threadLibControl = (ThreadLibControl) GetProcAddress (threadDLL, (LPCSTR) "omrthread_lib_control");
f_setCategory = (SetCategory) GetProcAddress (threadDLL, (LPCSTR) "omrthread_set_category");
f_libEnableCPUMonitor = (LibEnableCPUMonitor) GetProcAddress (threadDLL, (LPCSTR) "omrthread_lib_enable_cpu_monitor");
f_threadSleep = (ThreadSleep) GetProcAddress (threadDLL, (LPCSTR) "omrthread_sleep");
if (!f_threadGlobal || !f_threadAttachEx || !f_threadDetach || !f_monitorEnter || !f_monitorExit || !f_monitorInit
|| !f_monitorDestroy || !f_threadLibControl || !f_setCategory || !f_libEnableCPUMonitor
|| !f_monitorDestroy || !f_threadLibControl || !f_setCategory || !f_libEnableCPUMonitor || !f_threadSleep
) {
FreeLibrary(vmDLL);
FreeLibrary(threadDLL);
Expand Down Expand Up @@ -1442,8 +1445,9 @@ preloadLibraries(void)
f_threadLibControl = (ThreadLibControl) dlsym (threadDLL, "omrthread_lib_control");
f_setCategory = (SetCategory) dlsym (threadDLL, "omrthread_set_category");
f_libEnableCPUMonitor = (LibEnableCPUMonitor) dlsym (threadDLL, "omrthread_lib_enable_cpu_monitor");
f_threadSleep = (ThreadSleep) dlsym (threadDLL, "omrthread_sleep");
if (!f_threadGlobal || !f_threadAttachEx || !f_threadDetach || !f_monitorEnter || !f_monitorExit || !f_monitorInit
|| !f_monitorDestroy || !f_threadLibControl || !f_setCategory || !f_libEnableCPUMonitor
|| !f_monitorDestroy || !f_threadLibControl || !f_setCategory || !f_libEnableCPUMonitor || !f_threadSleep
) {
dlclose(vmDLL);
#ifdef J9ZOS390
Expand Down
2 changes: 1 addition & 1 deletion runtime/jvmti/jvmtiThread.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1326,7 +1326,7 @@ jvmtiSuspendResumeCallBack(J9VMThread *vmThread, J9MM_IterateObjectDescriptor *o
{
j9object_t continuationObj = object->object;
j9object_t vthread = J9VMJDKINTERNALVMCONTINUATION_VTHREAD(vmThread, continuationObj);
ContinuationState continuationState = J9VMJDKINTERNALVMCONTINUATION_STATE(vmThread, continuationObj);;
ContinuationState continuationState = J9VMJDKINTERNALVMCONTINUATION_STATE(vmThread, continuationObj);

if ((NULL != vthread) && J9_ARE_NO_BITS_SET(continuationState, J9_GC_CONTINUATION_STATE_LAST_UNMOUNT)) {
jvmtiVThreadCallBackData *data = (jvmtiVThreadCallBackData*)userData;
Expand Down