C++ thread pass value invoke constructor once and deconstructor many times,while pass ref it only invoke both constructor and deconstructor once

//Pass thread value type 
//Model//Util.h
#ifndef Util_H
#define Util_h
#include <ctime>
#include <chrono>
#include <iostream>
#include <sstream>
#include <thread>
#include <uuid/uuid.h>
#include <vector>

using namespace std;

class Util
{
public:
    static char *uuidValue;
    static char *dtValue;
    static int num;
    Util();
    ~Util();
    char *getTimeNow();
    char *getUuid(); 
    static void printUuidNum3(int x,Util ul);
    static void printNumUuid4(int x,Util ul);
    void mt5(int x,int y,Util ul);
};
#endif



//Model//Util.cpp

#include "Model/Util.h"

char *Util::dtValue = (char *)malloc(20);
char *Util::uuidValue = (char *)malloc(40);
int Util::num = 0;

void Util::mt5(int x, int y, Util ul)
{
    thread t1(printUuidNum3, x, ul);
    t1.join();

    thread t2(printNumUuid4, y,ul);
    t2.join();

    cout << getTimeNow() << ",finished in void Util::mt5(int x,int y,Util ul)!" << endl;
}

void Util::printNumUuid4(int x, Util ul)
{
    for (int i = 0; i < x; i++)
    {
        cout << i << "," << ul.getUuid() << endl;
    }
}

void Util::printUuidNum3(int x, Util ul)
{
    for (int i = 0; i < x; i++)
    {
        cout << ul.getUuid() << "," << i << endl;
    }
}

Util::Util()
{
    cout << ++num << ",In constructor!" << endl;
}

Util::~Util()
{
    cout << --num << ",In deconstructor!" << endl;
}


char *Util::getUuid()
{
    uuid_t newUUID;
    uuid_generate(newUUID);
    uuid_unparse(newUUID, uuidValue);
    return uuidValue;
}

char *Util::getTimeNow()
{
    time_t rawTime = time(NULL);
    struct tm tmInfo = *localtime(&rawTime);
    strftime(dtValue, 20, "%Y%m%d%H%M%S", &tmInfo);
    return dtValue;
}



//main.cpp

#include "Model/Util.h"

using namespace std;

void mt2(int x,int y);


int main(int args, char **argv)
{
    mt2(atoi(argv[1]), atoi(argv[2])); 
}

void mt2(int x,int y)
{ 
    Util ul;
    ul.mt5(x,y,ul); 
}

Compile

g++ -g -std=c++2a -I. *.cpp ./Model/*.cpp -o h1 -luuid -lpthread;

Run

time ./h1 5 5;

C++ thread pass value invoke constructor once and deconstructor many times,while pass ref it only invoke both constructor and deconstructor once

As the above snapshot illustrates,the constructor run only once,but the deconstructor run 8 times which confused me.

The constructor create the class instance only once,however the deconstructor can destory or dispose the instance 8 times.

//Model//Util.h
#ifndef Util_H
#define Util_h
#include <ctime>
#include <chrono>
#include <functional>
#include <iostream>
#include <sstream>
#include <thread>
#include <uuid/uuid.h>
#include <vector>

using namespace std;

class Util
{
public:
    static char *uuidValue;
    static char *dtValue;
    static int num;
    Util();
    ~Util();
    char *getTimeNow();
    char *getUuid(); 
    static void printUuidNum6(int x,Util &ul);
    static void printNumUuid7(int x,Util &ul);
    void mt8(int x,int y,Util &ul);
};
#endif


//Model//Util.cpp
#include "Model/Util.h"

int Util::num = 0;
char *Util::dtValue = (char *)malloc(20);
char *Util::uuidValue = (char *)malloc(40);

Util::Util()
{
    cout << ++num << ",In constructor!" << endl;
}

Util::~Util()
{
    cout << --num << ",In deconstructor!" << endl;
}

void Util::mt8(int x,int y,Util &ul)
{
    thread t1(printUuidNum6,x,std::ref(ul));
    t1.join();

    thread t2(printNumUuid7,y,std::ref(ul));
    t2.join();
    cout<<getTimeNow()<<", finished in void Util::mt8(int x,int y,Util &ul)!"<<endl;
}

void Util::printNumUuid7(int x,Util &ul)
{
    for(int i=0;i<x;i++)
    {
        cout<<i<<","<<ul.getUuid()<<endl;
    }
}

void Util::printUuidNum6(int x,Util &ul)
{
    for(int i=0;i<x;i++)
    {
        cout<<ul.getUuid()<<","<<i<<endl;
    }
}

char *Util::getUuid()
{
    uuid_t newUUID;
    uuid_generate(newUUID);
    uuid_unparse(newUUID, uuidValue);
    return uuidValue;
}

char *Util::getTimeNow()
{
    time_t rawTime = time(NULL);
    struct tm tmInfo = *localtime(&rawTime);
    strftime(dtValue, 20, "%Y%m%d%H%M%S", &tmInfo);
    return dtValue;
}


//main.cpp

#include "Model/Util.h"

using namespace std; 

void mt3(int x,int y);

int main(int args, char **argv)
{
    mt3(atoi(argv[1]), atoi(argv[2])); 
}

void mt3(int x,int y)
{
    Util ul;
    ul.mt8(x,y,std::ref(ul));
}

Compile

g++ -g -std=c++2a -I. *.cpp ./Model/*.cpp -o h1 -luuid -lpthread;

Run

time ./h1 10 10;

C++ thread pass value invoke constructor once and deconstructor many times,while pass ref it only invoke both constructor and deconstructor once

As the above snapshot illustrates that when I pass reference type in thread,it will only invoke deconstructor once.

原文链接: https://www.cnblogs.com/Fred1987/p/16395127.html

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C++ thread pass value invoke constructor once and deconstructor many times,while pass ref it only invoke both constructor and deconstructor once

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C++ thread pass value invoke constructor once and deconstructor many times,while pass ref it only invoke both constructor and deconstructor once

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