pthread 学习系列 case1-- 共享进程数据 VS 进程

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>


void *thread_foo_func(void *);
void *thread_bar_func(void *);


int global = 4;


int main(){
  int local = 8;
  int foo, bar;
  pthread_t fthread, bthread;
  foo = pthread_create(&fthread, NULL, thread_foo_func, (void *)&local);
  bar = pthread_create(&bthread, NULL, thread_bar_func, (void *)&local);
  if (foo != 0 || bar != 0){
    printf("thread creation failed.
");
    return -1;
  }


  foo = pthread_join(fthread, NULL);
  bar = pthread_join(bthread, NULL);
  if (foo != 0 || bar != 0){
    printf("thread join failed.
");
    return -2; 
  }


  printf("In thread main");
  printf("address of global %d: %x
", global, &global);
  printf("address of main local %d: %x
", local, &local);

  return 0;
}


void *thread_foo_func(void *arg){
  int foo_local = 16;
  global  ++;
  *(int *)arg = 10;
  printf("In thread foo_func");
  printf("address of global %d: %x
", global, &global);
  printf("address of main local %d: %x
", *(int *)arg, arg);
  printf("address of foo local: %x
", &foo_local);
  printf("
");
}


void *thread_bar_func(void *arg){
  int bar_local = 32;
  global  ++;
  *(int *)arg = 20;
  printf("In thread bar_func");
  printf("address of global %d: %x
", global, &global);
  printf("address of main local %d: %x
", *(int *)arg, arg);
  printf("address of bar local: %x
", &bar_local);
  printf("
");
}

打印输出结果

In thread foo_funcaddress of global 5: 8049a48
address of main local 10: bfc567b8
address of foo local: b7f553c4

In thread bar_funcaddress of global 6: 8049a48
address of main local 20: bfc567b8
address of bar local: b75543c4

In thread mainaddress of global 6: 8049a48
address of main local 20: bfc567b8

可见：

1 global 在线程中可见，而且共享，

2 main中的loca通过指针传给了进程，进程可以改变

3 两个线程中的私有变量是不同的，是线程私有的。

这和fork出的进程就完全不同

int global = 6;

int main(int argc,char** argv)
{
    int var=10;
    int pid=fork();
    if(pid==-1){
        printf("error!");
    }   
    else if(pid==0){
        global++;
        var++;
        printf("This is the child process!
");
    }   
    else{
        printf("This is the parent process! child processid=%d
",pid);
    }   
    printf("%d, %d, %d 
", getpid(), global, var); 

    return 1;                                                                                                                           
}

打印结果：

This is the child process!
10769, 7, 11 
This is the parent process! child processid=10769
10768, 6, 10 

可见，调用fork，会有两次返回，一次是父进程、一次是子进程，因为子进程是父进程的副本，所以它拥有父进程数据空间、栈和堆的副本，它们并没有共享这些存储空间，它们只共享正文段。