fork.md

fork

The fork() system call will spawn a new child process which is an identical process to the parent and returns a process ID. The purpose of fork() is to create a child process for the caller. After calling fork function, the code below the fork() would be executed by both process, parent and child. To discriminate which process should do what, we check pID

int globalVariable = 2;

int main()
{
    std::cout<<"The code before fork(), it runs only by parent" <<std::endl;
    std::string sIdentifier;
    int    iStackVariable = 20;

    pid_t pID = fork();
    /*
    after calling fork function, the below code would be executed by both process, parent and child
    to discriminet which process should do what, we check pID
    */
    if (pID == 0)                // child
    {
        // Code only executed by child process

        sIdentifier = "Child Process: ";
        globalVariable++;
        iStackVariable++;
    }
    else if (pID < 0)            // failed to fork
    {
        std::cerr << "Failed to fork" << std::endl;
        exit(1);
        // Throw exception
    }
    else                                   // parent
    {
    // Code only executed by parent process

        sIdentifier = "Parent Process:";
    }

    // Code executed by both parent and child.

    pid_t pid = getpid();
    std::cout <<sIdentifier<<" pid:  "<< pid<<std::endl;
    std::cout << " Global variable: " << globalVariable;
    std::cout << " Stack variable: "  << iStackVariable << std::endl;
}

Refs: 1, 2

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