Graal AOT is 12x times slower then JVM doing trivial native calls

[kirillp]

Assume we need to communicate with "C", and we dont need complex JNI like call a method
Assume the following code:
static native int call(int[] arr);

Testsource code:

JniTest.cpp
JniTest.java

Build commands
native-image.cmd --no-fallback -cp . test.JniTest
cl /I%JAVA_HOME%\include /I%JAVA_HOME%\include\win32 /LD /O1 /FAs JniTest.cpp /link /noentry

• GraalVM version graalvm-ce-java11-20.2.0
• JDK major version: 14
• OS: windows
• Architecture: AMD64

This is my results, numbers is time spent, lower better:
Graal:
min critical: 989800
min non critical: 984400
Jvm
min critical: 84200
min non critical: 558200

[christianwimmer]

While there is probably room for improvement, there is a fundamental difference how GetPrimitiveArrayCritical is implemented on SVM vs. HotSpot: while HotSpot just disables the GC while a critical array is requested, SVM properly just pins that single object. This has far less severe side effects on the GC, on HotSpot JNI code that uses GetPrimitiveArrayCritical can let the VM run out of memory because no GC is possible anymore.

[kirillp]

Is there a better way to pass
float data[] = new float[16];
to a @CFunction somehow to invoke ?
extern "C" void getMatrix(float *);

Can I use org.grallvm.naiveimage.c interop somehow here ?

[christianwimmer]

You can pass pointers into primitive arrays to C functions if you "pin" the array, i.e., prevent it from being moved while C code might access it. The API for pinning is in https://github.com/oracle/graal/blob/fe2ba8d03ae8c032da8f2c0f467117b5a56991e2/sdk/src/org.graalvm.nativeimage/src/org/graalvm/nativeimage/PinnedObject.java

[kirillp]

<T extends PointerBase> T addressOfArrayElement(int index);

Sounds good. It is not clear for me how to use it later on.

Should I use
extern "C" JNIEXPORT jint JNICALL Java_test_JniTest_getMatrix(JNIEnv * env, jclass c, void *array);
instead of
extern "C" JNIEXPORT jint JNICALL Java_test_JniTest_getMatrix(JNIEnv * env, jclass c, jintArray array);
?
Can I avoid "JNIEnv * env, jclass" somehow ?

[christianwimmer]

When using @CFunction, you just define your function as extern "C" void getMatrix(float *); on the C side. No JNI parameters involved at all.

[kirillp]

sounds good, will take a look

[christianwimmer]

btw, examples how to use @CFunction are in https://github.com/oracle/graal/blob/master/substratevm/src/com.oracle.svm.tutorial/src/com/oracle/svm/tutorial/CInterfaceTutorial.java