JNI Construction Benchmark

2017-2-7 13:39| 发布者: zhangjf| 查看: 700| 评论: 0

摘要: JNI Construction Benchmark We provide the code for a small benchmark to compare the costs of JNI object creation, and then present theresults. The code contrasts three different approaches to constr ...

We provide the code for a small benchmark to compare the costs of JNI object creation, and then present theresults.

The code contrasts three different approaches to constructing a Java Object that wraps a C++ object (which it has to construct). Such a scenario is common when writing a Java API wrapper for an existing C++ project.

Scenario 1 - By Call

From Java we call a JNI C++ member function to construct the C++ object and return a jlong which represents the memory pointer to the C++ object.

public class FooByCall extends NativeBackedObject {
public FooByCall() {
super();
this._nativeHandle = newFoo();
}
private native long newFoo();
...

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jlong Java_com_evolvedbinary_jni_consbench_FooByCall_newFoo(JNIEnv* env, jobject jobj) {
consbench::Foo* foo = new consbench::Foo();
return reinterpret_cast<jlong>(foo);
}

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Scenario 2 - By Call, Static

Similar to Scenario 1 , except that we use a static call to a JNI C++ function.

public class FooByCallStatic extends NativeBackedObject {
public FooByCallStatic() {
super();
this._nativeHandle = newFoo();
}
private static native long newFoo();
...

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jlong Java_com_evolvedbinary_jni_consbench_FooByCallStatic_newFoo(JNIEnv* env, jclass jcls) {
consbench::Foo* foo = new consbench::Foo();
return reinterpret_cast<jlong>(foo);
}

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Scenario 3 - By Call, Invoke

Similar to Scenario 1 , however instead of returning a jlong pointer, we instead in C++ find the _nativeHandle member of the calling Java object, and then directly set the long field from C++.

public class FooByCallInvoke extends NativeBackedObject {
public FooByCallInvoke() {
super();
newFoo(); //the native method, will find _nativeHandle from the class and set it directly
}
private native void newFoo();
...

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void Java_com_evolvedbinary_jni_consbench_FooByCallInvoke_newFoo(JNIEnv* env, jobject jobj) {
consbench::Foo* foo = new consbench::Foo();
//set the _nativeHandle in Java
consbench::FooByCallInvokeJni::setHandle(env, jobj, foo);
}
template<class PTR, class DERIVED> class FooJniClass {
public:
// Get the java class id
static jclass getJClass(JNIEnv* env, const char* jclazz_name) {
jclass jclazz = env->FindClass(jclazz_name);
assert(jclazz != nullptr);
return jclazz;
}
// Get the field id of the member variable to store
// the ptr
static jfieldID getHandleFieldID(JNIEnv* env) {
static jfieldID fid = env->GetFieldID(
DERIVED::getJClass(env), "_nativeHandle", "J");
assert(fid != nullptr);
return fid;
}
// Get the pointer from Java
static PTR getHandle(JNIEnv* env, jobject jobj) {
return reinterpret_cast<PTR>(
env->GetLongField(jobj, getHandleFieldID(env)));
}
// Pass the pointer to the java side.
static void setHandle(JNIEnv* env, jobject jdb, PTR ptr) {
env->SetLongField(
jdb, getHandleFieldID(env),
reinterpret_cast<jlong>(ptr));
}
};
// The portal class for com.evolvedbinary.jni.consbench.FooByCallInvoke
class FooByCallInvokeJni : public FooJniClass<consbench::Foo*, FooByCallInvokeJni> {
public:
static jclass getJClass(JNIEnv* env) {
return FooJniClass::getJClass(env,
"com/evolvedbinary/jni/consbench/FooByCallInvoke");
}
};

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Results

Test machine: MacBook Pro Retina Mid-2015: 2.8 GHz Intel Core i7 / 16 GB 1600 MHz DDR3.

$ java -version
java version "1.8.0_51"
Java(TM) SE Runtime Environment (build 1.8.0_51-b16)
Java HotSpot(TM) 64-Bit Server VM (build 25.51-b03, mixed mode)

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The com.evolvedbinary.jni.consbench.Benchmark class already calls each scenario 1,000,000 times, so for the benchmark we repeated this 100 times and plotted the results.

Conclusion

Scenario 2 - By Call, Static, appears to have the lowest JNI overhead for constructing C++ objects from Java.

Reproducing

If you want to run the code yourself, you need to have Java 8, Maven 3, and a C++ compiler that supports the C++ 11 standard. You can then simply run:

$ mvn clean compile package

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In the target/ sub-directory, you will then find both a jni-construction-benchmark-1.0-SNAPSHOT-application folder and a jni-construction-benchmark-1.0-SNAPSHOT-application.zip file, you can use either of these. They both contain bash scripts in their bin/ sub-folders for Mac, Linux, Unix and batch scripts for Windows.

来自： https://github.com/adamretter/jni-construction-benchmark

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