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pthread 学习系列 case1

2024-07-13 23:21:33   220人阅读

 

 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: 8049a48address of main local 10: bfc567b8address of foo local: b7f553c4In thread bar_funcaddress of global 6: 8049a48address of main local 20: bfc567b8address of bar local: b75543c4In thread mainaddress of global 6: 8049a48address 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=1076910768, 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。 


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