Question

我试图从Java调用C函数。 C函数使用openmp并行for循环。但是，在程序完成后，结果显示只使用了一个线程。所以，我想知道将openmp与JNI一起使用是否可行。

由于

以下是我的clang信息和makefile的内容：

clang version 3.5.0 
Target: x86_64-apple-darwin15.0.0
Thread model: posix


CC = gcc
CLANG = clang-omp
CFLAGS = -c -Wall -fPIC -std=c11
OMP = -fopenmp
LIBFLAG = -dynamiclib
INCPATH = -I/Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/include -I/usr/local/Cellar/libiomp/20150701/include/libiomp -I/Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/include/darwin -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk/System/Library/Frameworks/JavaVM.framework/Versions/A/Headers
LIBPATH = -L./ -L/usr/local/Cellar/libiomp/20150701/lib -lepanet -liomp5
all: library

library: *.o
    $(CC) $(LIBFLAG) $(OMP) -o libJNIFitness.jnilib *.o 

*.o: *.c
    $(CC) $(OMP) $(CFLAGS) $(INCPATH) *.c

clean:
    rm *.o libJNIFitness.jnilib

Answer 1

当然，您可以在JNI方法中运行OpenMP。请观看以下示例（包括JNI代码[Java和C-counter-side]和Makefile）。它使用几个线程通过近似计算pi，在计算之前，每个线程在屏幕上标识自己。

您可能需要调整它，将CC和JDK变量更改为您的环境以及一些Linux / gcc vs MacOsX / clang标志（例如将-fPIC -DPIC更改为-dynamiclib等）。然后你可以通过执行：

来运行它

make run

并输出以下内容

LD_LIBRARY_PATH=. JNItest
within Java_JNItest_CalculatePi
Java_JNItest_calculatepi: I'm thread 0 out of 4
Java_JNItest_calculatepi: I'm thread 2 out of 4
Java_JNItest_calculatepi: I'm thread 1 out of 4
Java_JNItest_calculatepi: I'm thread 3 out of 4
returning to Java...
In Java, the value of pi is 3.1415926535896825

档案 JNItest.java

public class JNItest
{
    static { System.loadLibrary("pi"); }

    public static native double CalculatePi (long nsteps);

    public static void main(String args[])
    {
        System.out.println ("In Java, the value of pi is " +
          new JNItest().CalculatePi(100_000_000));
    }
}

档案 pi.c

#include <stdio.h>
#include <JNItest.h>

JNIEXPORT jdouble JNICALL Java_JNItest_CalculatePi
  (JNIEnv * env, jclass jc, jlong nsteps)
{
    jdouble h, area, x;

    printf ("within Java_JNItest_CalculatePi\n");

    h = 1.0 / (jdouble) nsteps;
    area = 0.0;
    #pragma omp parallel private(x)
    {
        int i;
        printf ("Java_JNItest_calculatepi: I'm thread %d out of %d\n",
            omp_get_thread_num(), omp_get_num_threads());

        #pragma omp for reduction(+:area)
        for (i = 1; i <= nsteps; i++)
        {
            x = h * ((double)i - 0.5);
            area += (4.0 / (1.0 + x*x));
        }
    }

    printf ("returning to Java...\n");

    return h * area;
}

文件 makefile

all: JNItest.class libpi.so

CC=gcc
JDK=/usr/lib/jvm/java-7-openjdk-amd64

JNItest.class: JNItest.java
    $(JDK)/bin/javac JNItest.java

JNItest.h: JNItest.java
    $(JDK)/bin/javah JNItest

libpi.so: JNItest.h
    $(CC) -fopenmp -fPIC -DPIC pi.c -I. -I$(JDK)/include -shared -o libpi.so

clean:
    rm libpi.so JNItest.h JNItest.class

run: JNItest.class libpi.so
    LD_LIBRARY_PATH=$(PWD):$(LD_LIBRARY_PATH) $(JDK)/bin/java JNItest

JNI与openmp

1 个答案: