CODEWITHSUNDEEP
javaperformancejava-native-interfacemeasureelapsedtime
LGProgramer
LGProgramer

Reputation: 45

Measure time in Java JNI ( native call Java)

I am trying to measure time in JNI call, it call from native to Java.

In C code, I apply "GetTickCount" api to get JNI execution time and "System.nano" in Java.

Example:

long start = GetTickCount();
....//CallStaticMethod exampleMethod...
long end = GetTickCount();
long duration = end - start;

And in Java

public static exampleMethod(){
    long start = System.nano();
    //do something
    long end = System.nano();
    long duration = TimeUnit.NANOSECONDS.toMilis(end - start);
}

Sometimes, it is inconsistent because the java's duration is more than C's duration. ( about 5 to 10 miliseconds)

Upvotes: 3

Views: 1249

Answers (2)

apangin
apangin

Reputation: 98630

GetTickCount and System.nanoTime() use different time sources.

The problem with GetTickCount is its very poor resolution, usually around 10ms. This is explicitly remarked in the documentation:

The resolution of the GetTickCount function is limited to the resolution of the system timer, which is typically in the range of 10 milliseconds to 16 milliseconds.

No wonder that it can differ from nanoTime that much.

To make measurements consistent with System.nanoTime, use higher resolution timer by calling either QueryPerformanceCounter or GetSystemTimeAsFileTime.

EDIT

JDK's System.nanoTime() is implemented on top of QueryPerformanceCounter (the source).

Upvotes: 2

user1257043
user1257043

Reputation:

On the java side of things you will always be at the mercy of the JVM :

http://shipilev.net/blog/2014/nanotrusting-nanotime/

Upvotes: 0

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