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 = ;

 int main(){
   int local = ;
   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 !=  || bar != ){
     printf("thread creation failed.\n");
     return -;
   }

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

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

   return ;
 }

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

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

打印输出结果

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

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

In thread mainaddress of global : 8049a48
address of main local : 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 = ;

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

     return ;
 }

打印结果：

This is the child process!
, ,
This is the parent process! child processid=
, ,  

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。