pthread 学习系列 case1

 1 #include <stdio.h>
 2 #include <unistd.h>
 3 #include <stdlib.h>
 4 #include <pthread.h>
 5
 6
 7 void *thread_foo_func(void *);
 8 void *thread_bar_func(void *);
 9
10
11 int global = 4;
12
13
14 int main(){
15   int local = 8;
16   int foo, bar;
17   pthread_t fthread, bthread;
18   foo = pthread_create(&fthread, NULL, thread_foo_func, (void *)&local);
19   bar = pthread_create(&bthread, NULL, thread_bar_func, (void *)&local);
20   if (foo != 0 || bar != 0){
21     printf("thread creation failed.\n");
22     return -1;
23   }
24
25
26   foo = pthread_join(fthread, NULL);
27   bar = pthread_join(bthread, NULL);
28   if (foo != 0 || bar != 0){
29     printf("thread join failed.\n");
30     return -2;
31   }
32
33
34   printf("In thread main");
35   printf("address of global %d: %x\n", global, &global);
36   printf("address of main local %d: %x\n", local, &local);
37
38   return 0;
39 }
40
41
42 void *thread_foo_func(void *arg){
43   int foo_local = 16;
44   global  ++;
45   *(int *)arg = 10;
46   printf("In thread foo_func");
47   printf("address of global %d: %x\n", global, &global);
48   printf("address of main local %d: %x\n", *(int *)arg, arg);
49   printf("address of foo local: %x\n", &foo_local);
50   printf("\n");
51 }
52
53
54 void *thread_bar_func(void *arg){
55   int bar_local = 32;
56   global  ++;
57   *(int *)arg = 20;
58   printf("In thread bar_func");
59   printf("address of global %d: %x\n", global, &global);
60   printf("address of main local %d: %x\n", *(int *)arg, arg);
61   printf("address of bar local: %x\n", &bar_local);
62   printf("\n");
63 }

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

 1 int global = 6;
 2
 3 int main(int argc,char** argv)
 4 {
 5     int var=10;
 6     int pid=fork();
 7     if(pid==-1){
 8         printf("error!");
 9     }
10     else if(pid==0){
11         global++;
12         var++;
13         printf("This is the child process!\n");
14     }
15     else{
16         printf("This is the parent process! child processid=%d\n",pid);
17     }
18     printf("%d, %d, %d \n", getpid(), global, var);
19
20     return 1;
21 }

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。

pthread 学习系列 case1