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Add stronger guarantees to System.gc()
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The JCL code expects that when System.GC() is called a GC occurs and
finalizable objects are finalized. Historically, J9 has never provided
this guarantee. We have often had to modify tests to ensure a GC is
triggered at the appropriate time. Increasingly, we are finding that
more and more tests rely on this behaviour, and most importantly, core
JCL code now relies on this behaviour. This PR ensures that a call to
System.gc() triggers a GC and runs finalization.

Signed-off-by: tajila <[email protected]>
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@tajila
tajila committed Aug 30, 2023
1 parent 553cb6a commit 213d001
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Showing 2 changed files with 46 additions and 25 deletions.
4 changes: 4 additions & 0 deletions runtime/jcl/common/java_lang_ref_Finalizer.c
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Original file line number Diff line number Diff line change
Expand Up @@ -40,4 +40,8 @@ Java_java_lang_ref_Finalizer_runFinalizationImpl(JNIEnv *env, jclass recv)
vmFuncs->internalReleaseVMAccess(currentThread);
#endif /* J9VM_INTERP_ATOMIC_FREE_JNI */
mmFuncs->runFinalization(currentThread);
#if defined(J9VM_INTERP_ATOMIC_FREE_JNI)
vmFuncs->internalAcquireVMAccess(currentThread);
vmFuncs->internalExitVMToJNI(currentThread);
#endif /* J9VM_INTERP_ATOMIC_FREE_JNI */
}
67 changes: 42 additions & 25 deletions runtime/sunvmi/sunvmi.c
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Original file line number Diff line number Diff line change
Expand Up @@ -22,10 +22,10 @@

/**
* @brief This file contains implementations of the Sun VM interface (JVM_ functions).
*
*
* In a VM-Proxy environment all functions in this file are expected to run VM-side,
* and are compiled into the offload services via vpath.
*
* and are compiled into the offload services via vpath.
*
* On the launcher-side we compile in forwarders for JVM_ by reusing code declared
* in the redirector.
*/
Expand Down Expand Up @@ -69,7 +69,7 @@ typedef struct SunVMGlobals {
/* Thread library functions looked up dynamically */
IDATA (*monitorEnter)(omrthread_monitor_t monitor);
IDATA (*monitorExit)(omrthread_monitor_t monitor);

/* stores the current_time_millis at the last GLOBAL_GC_END event */
I_64 lastGCTime;

Expand Down Expand Up @@ -169,7 +169,7 @@ static UDATA
getCallerClassIterator(J9VMThread * currentThread, J9StackWalkState * walkState)
{
J9JavaVM * vm = currentThread->javaVM;


if (J9_ARE_ALL_BITS_SET(J9_ROM_METHOD_FROM_RAM_METHOD(walkState->method)->modifiers, J9AccMethodFrameIteratorSkip)) {
/* Skip methods with java.lang.invoke.FrameIteratorSkip / jdk.internal.vm.annotation.Hidden / java.lang.invoke.LambdaForm$Hidden annotation */
Expand Down Expand Up @@ -214,7 +214,7 @@ getCallerClassJEP176Iterator(J9VMThread * currentThread, J9StackWalkState * walk
J9JavaVM * vm = currentThread->javaVM;
J9InternalVMFunctions *vmFuncs = vm->internalVMFunctions;
J9Class * currentClass = J9_CLASS_FROM_CP(walkState->constantPool);

Assert_SunVMI_mustHaveVMAccess(currentThread);

if (J9_ARE_ALL_BITS_SET(J9_ROM_METHOD_FROM_RAM_METHOD(walkState->method)->modifiers, J9AccMethodFrameIteratorSkip)) {
Expand Down Expand Up @@ -274,9 +274,9 @@ JVM_GetCallerClass_Impl(JNIEnv *env, jint depth)
/* Java 11 removed getCallerClass(depth), and getCallerClass() is equivalent to getCallerClass(-1) */
jint depth = -1;
#endif /* JAVA_SPEC_VERSION >= 11 */

Trc_SunVMI_GetCallerClass_Entry(env, depth);

walkState.frameWalkFunction = getCallerClassIterator;

if (-1 == depth) {
Expand Down Expand Up @@ -352,7 +352,7 @@ JVM_NewInstanceFromConstructor_Impl(JNIEnv * env, jobject c, jobjectArray args)
/**
* JVM_InvokeMethod
*/
JNIEXPORT jobject JNICALL
JNIEXPORT jobject JNICALL
JVM_InvokeMethod_Impl(JNIEnv * env, jobject method, jobject obj, jobjectArray args)
{
J9VMThread *vmThread = (J9VMThread *) env;
Expand Down Expand Up @@ -382,7 +382,7 @@ JVM_GetClassAccessFlags_Impl(JNIEnv * env, jclass clazzRef)
Trc_SunVMI_GetClassAccessFlags_Entry(env, clazzRef);

vmFuncs->internalEnterVMFromJNI(vmThread);

if (clazzRef == NULL) {
Trc_SunVMI_GetClassAccessFlags_NullClassRef(env);
vmFuncs->setCurrentException(vmThread, J9VMCONSTANTPOOL_JAVALANGNULLPOINTEREXCEPTION, NULL);
Expand All @@ -394,7 +394,7 @@ JVM_GetClassAccessFlags_Impl(JNIEnv * env, jclass clazzRef)
} else {
modifiers = romClass->modifiers & 0xFFFF;
}
}
}
vmFuncs->internalExitVMToJNI(vmThread);

Trc_SunVMI_GetClassAccessFlags_Exit(env, modifiers);
Expand All @@ -403,7 +403,7 @@ JVM_GetClassAccessFlags_Impl(JNIEnv * env, jclass clazzRef)
}


static jint
static jint
initializeReflectionGlobals(JNIEnv * env,BOOLEAN includeAccessors) {
J9VMThread *vmThread = (J9VMThread *) env;
J9JavaVM * vm = vmThread->javaVM;
Expand All @@ -429,7 +429,7 @@ initializeReflectionGlobals(JNIEnv * env,BOOLEAN includeAccessors) {
return JNI_ERR;
}
#endif /* defined(J9VM_OPT_METHOD_HANDLE) && !defined(J9VM_IVE_RAW_BUILD) */

if (J2SE_VERSION(vm) >= J2SE_V11) {
clazzConstructorAccessorImpl = (*env)->FindClass(env, "jdk/internal/reflect/ConstructorAccessorImpl");
clazzMethodAccessorImpl = (*env)->FindClass(env, "jdk/internal/reflect/MethodAccessorImpl");
Expand All @@ -450,7 +450,7 @@ initializeReflectionGlobals(JNIEnv * env,BOOLEAN includeAccessors) {
if (NULL == vm->srMethodAccessor) {
return JNI_ERR;
}

return JNI_OK;
}

Expand Down Expand Up @@ -612,13 +612,30 @@ getClassContextIterator(J9VMThread * currentThread, J9StackWalkState * walkState
JNIEXPORT void JNICALL
JVM_GC_Impl(void)
{
J9VMThread *currentThread = VM.javaVM->internalVMFunctions->currentVMThread(VM.javaVM);
J9InternalVMFunctions *vmFuncs = VM.javaVM->internalVMFunctions;
J9VMThread *currentThread = vmFuncs->currentVMThread(VM.javaVM);
J9MemoryManagerFunctions *mmFuncs = VM.javaVM->memoryManagerFunctions;

Trc_SunVMI_GC_Entry(currentThread);

VM.javaVM->internalVMFunctions->internalEnterVMFromJNI(currentThread);
VM.javaVM->memoryManagerFunctions->j9gc_modron_global_collect(currentThread);
VM.javaVM->internalVMFunctions->internalExitVMToJNI(currentThread);
#if defined(J9VM_INTERP_ATOMIC_FREE_JNI)
vmFuncs->internalEnterVMFromJNI(currentThread);
#else /* J9VM_INTERP_ATOMIC_FREE_JNI */
vmFuncs->internalAcquireVMAccess(currentThread);
#endif /* J9VM_INTERP_ATOMIC_FREE_JNI */

mmFuncs->j9gc_modron_global_collect(currentThread);
mmFuncs->j9gc_modron_global_collect(currentThread);

/* make sure we actually release VMAccess as finalization cannot be run with it */
vmFuncs->internalReleaseVMAccess(currentThread);

mmFuncs->runFinalization(currentThread);

#if defined(J9VM_INTERP_ATOMIC_FREE_JNI)
vmFuncs->internalAcquireVMAccess(currentThread);
vmFuncs->internalExitVMToJNI(currentThread);
#endif /* J9VM_INTERP_ATOMIC_FREE_JNI */

Trc_SunVMI_GC_Exit(currentThread);
}
Expand Down Expand Up @@ -1088,7 +1105,7 @@ internalFindClassFromClassLoader(JNIEnv* env, char* className, jboolean init, jo

initializeSent = TRUE;

/* Check for a pending exception directly, do not use ExceptionCheck as it will
/* Check for a pending exception directly, do not use ExceptionCheck as it will
cause jnichk to dump an error since we are calling it with vm access */
if (currentThread->currentException != NULL) {
clazz = NULL;
Expand Down Expand Up @@ -1125,7 +1142,7 @@ typedef struct {

/**
* This is an helper function to call internalFindClassFromClassLoader indirectly from gpProtectAndRun function.
*
*
* @param entryArg Argument structure (J9RedirectedFindClassFromClassLoaderArgs).
*/
static UDATA
Expand All @@ -1145,14 +1162,14 @@ gpProtectedInternalFindClassFromClassLoader(void * entryArg)
* @param throwError set to true in order to throw errors
* @return Assumed to be a jclass.
*
*
*
*/
JNIEXPORT jobject JNICALL
JVM_FindClassFromClassLoader_Impl(JNIEnv* env, char* className, jboolean init, jobject classLoader, jboolean throwError)
{
if (NULL == env) {
return NULL;
}
}

if (((J9VMThread*) env)->gpProtected) {
return internalFindClassFromClassLoader(env, className, init, classLoader, throwError);
Expand Down Expand Up @@ -1180,13 +1197,13 @@ static BOOLEAN
initializeThreadFunctions(J9JavaVM *vm)
{
PORT_ACCESS_FROM_PORT(vm->portLibrary);

if (0 != j9sl_lookup_name(vm->threadDllHandle, "omrthread_monitor_enter", (UDATA*)&VM.monitorEnter, NULL)) {
return FALSE;
return FALSE;
}

if (0 != j9sl_lookup_name(vm->threadDllHandle, "omrthread_monitor_exit", (UDATA*)&VM.monitorExit, NULL)) {
return FALSE;
return FALSE;
}

return TRUE;
Expand Down

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