如何在Java项目中与C++混合开发 发布于

1. 压缩包直接解压，第一步中大部分用户会遇到`The file has been downloaded incorrectly!`问题导致安装失败，所以我更推荐第二种安装方法： 
    1. 在mingw-w64页面底部下载[x86\_64-win32-seh](https://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win64/Personal%20Builds/mingw-builds/8.1.0/threads-win32/seh/x86_64-8.1.0-release-win32-seh-rt_v6-rev0.7z)
    2. 将压缩包解压到合适的位置后将目录中的`bin`文件夹添加到环境变量中完成安装安装并配置环境变量完成后在cmd中使用命令

public class CPUWatchDog {
	public CPUWatchDog() {}
	
	// native area
	public native double getCPULoad(int cpuIndex); // for single cpu core
	public native double[] getBatchCPULoad(); // for cpu core matrix
}

	#include <jni.h>
	#include "cn_____CPUWatchDog.h" // 在同级目录下引入头文件

	// for single cpu core
	JNIEXPORT jdouble JNICALL Java_cn_____CPUWatchDog_getCPULoad
	(JNIEnv *env, jobject obj, jint cpuIndex)
	{
	}
	// for cpu matrix
	JNIEXPORT jdoubleArray JNICALL Java_cn_____CPUWatchDog_getBatchCPULoad  
	(JNIEnv *env, jobject obj)
	{
	}

	cmake_minimum_required(VERSION 3.25)
	project(native)

	set(CMAKE_CXX_STANDARD 11)  # C++版本

	include_directories(.)
	include_directories("C:/Program Files/Java/jdk-17.0.3.1/include")        # 引入jdk17的函数依赖
	include_directories("C:/Program Files/Java/jdk-17.0.3.1/include/win32")  # 引入jdk17的函数依赖

	add_library(CPUWatchDog SHARED        # 工程名称 构建方式
				CPUWatchDog.cpp           # 源文件
				cn_____CPUWatchDog.h)     # 头文件

	target_link_libraries(CPUWatchDog pdh pthread)  # 额外的动态链接库
	set_target_properties(CPUWatchDog PROPERTIES    # 编译输出配置
						  RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/../resources/native"   # 输出目录
						  LIBRARY_OUTPUT_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/../resources/native")  # 输出目录

#include <jni.h>
#include <pdh.h>
#include <vector>
#include "cn_____CPUWatchDog.h"

extern "C"
{
#include <pthread.h>
}

/**
 * 获取本计算机的最大核心数
 */
int getNumberOfCores()
{
	SYSTEM_INFO sysInfo;
	GetSystemInfo(&sysInfo);
	return sysInfo.dwNumberOfProcessors;
}
  
/**
 * 封装获取单个CPU核心的使用率函数
 * @param cpuIndex CPU的唯一编号（默认从0开始到最大核心数-1）
 */
double getSingleCpuUsePercentage(int cpuIndex)
{
	PDH_HQUERY query;
	PDH_HCOUNTER counter;
	wchar_t counterPath[256];
	
	swprintf_s(counterPath, sizeof(counterPath), L"\\Processor(%d)\\%% Processor Time", cpuIndex);
	PdhOpenQuery(nullptr, 0, &query);
	PdhAddCounterW(query, counterPath, 0, &counter);
	PdhCollectQueryData(query);
	Sleep(1000);
	PdhCollectQueryData(query);
	PDH_FMT_COUNTERVALUE pdhValue;
	DWORD dwValue;
	PdhGetFormattedCounterValue(counter, PDH_FMT_DOUBLE, &dwValue, &pdhValue);
	PdhCloseQuery(query);
	return pdhValue.doubleValue;
}

/**
 * 获取单个CPU核心的使用率
 */
JNIEXPORT jdouble JNICALL Java_cn_____CPUWatchDog_getCPULoad
(JNIEnv *env, jobject obj, jint cpuIndex)
{
	return getSingleCpuUsePercentage(cpuIndex);
}

/**
 * 获取单个CPU核心的使用率但是需要返回一个指针来防止常量被销毁
 */
void *getSingleCpuUsePercentageWrapper(void *args)
{
	int core = *((int*)args);
	double load = getSingleCpuUsePercentage(core);
	return (void*)(new double(load));
}

/**
 * 获取所有CPU核心的使用率并以数组返回
 */
JNIEXPORT jdoubleArray JNICALL Java_cn_____CPUWatchDog_getBatchCPULoad  
(JNIEnv *env, jobject obj)
{
	int SIZE = getNumberOfCores();
	// 创建一个长度为SIZE的Java类型的double[]数组
	jdoubleArray arrayArray = env->NewDoubleArray(SIZE);
	jdouble *elements = env->GetDoubleArrayElements(arrayArray, 0);
	std::vector<pthread_t> threads(SIZE);
	std::vector<int> cores(SIZE);
	for (int i = 0; i < SIZE; i++)
	{
		cores[i] = i;
		pthread_create(&threads[i], nullptr, getSingleCpuUsePercentageWrapper, &cores[i]);
	}
	
	for (int i = 0; i < SIZE; i++)
	{
		double *result;
		pthread_join(threads[i], (void**)&result);
		elements[i] = *result;
		delete result;
	}
	
	env->ReleaseDoubleArrayElements(arrayArray, elements, 0);
	return arrayArray;
}

C:\...\cmake.exe -DCMAKE_BUILD_TYPE=Debug -DCMAKE_MAKE_PROGRAM=C:/.../ninja.exe -G Ninja -S C:\...\native -B C:\...\cmake-build-debug
-- Configuring done
-- Generating done
-- Build files have been written to: C:/.../cmake-build-debug

[Finished]

public class CPUWatchDog {
	static {
		URL resource = CPUWatchDog.class.getResource("/native/libCPUWatchDog.dll");
		if (resource == null)
			throw new Error("can't find native source from /native/libCPUWatchDog.dll");
		File file = new File(resource.getFile());
		System.load(file.getAbsolutePath());
	}
	// ...
}

public class AppUnitTest {
	CPUWatchDog watchDog = new CPUWatchDog();
	@Test
	public void cpuUnitTest() {
		DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
		LocalDateTime currentTime = LocalDateTime.now();
		System.out.println("[" + currentTime.format(formatter) + " CPU-Monitor]" + Arrays.toString(watchDog.getBatchCPULoad()));
	}
}