fork mmap 共享映射区

傷城~ 2022-08-12 01:06 243阅读 0赞

\#include <sys/types.h>  
\#include <unistd.h>  
pid\_t fork(void);

fork 调用失败则返回-1

//fork 创建一个子进程
    #include <stdio.h>
    #include <unistd.h>
    
    int main(void)
    {
    	pid_t pid;
    
    	pid = fork();
    
    	if(pid == 0){
    		printf("child\n");
    	} else {
    		printf("parent\n");
    	}
    
    	return 0;
    }
    
    /*
    $ ./fork
    parent
    child
    */<pre name="code" class="cpp">
    
    
    
    
    
    
    
    
    
    
    
    
    /*
    creat parent child
    */
    
    #include <stdio.h>
    #include <unistd.h>
    #include <stdlib.h>
    
    int main(void)
    {
    	pid_t pid;
    	char *message;
    	int n;
    
    	pid = fork();
    	if(pid == -1){
    		perror("fork error");
    		exit(1);
    	}else if(pid == 0){
    		printf("i'am child, pid = %d\n", getpid());
    		printf("parent id = %d\n", getppid());
    
    	}else if(pid > 0){
    		printf("parent, pid = %d\n", getpid());
    	}
    
    	return 0;
    
    }
    
    /*akaedu@akaedu-G41MT-D3:~/lin/20140828_fock$ ./4
    parent, pid = 7034
    i'am child, pid = 7035
    parent id = 7034
    */
    
    
    <pre name="code" class="cpp">/*
    creat 5 child
    循环创建５个子进程
    */
    
    #include <stdio.h>
    #include <unistd.h>
    #include <stdlib.h>
    
    int main(int argc, char *argv[])
    {
    	int n = 5, i;			   //默认创建5个子进程
    
    	if(argc == 2){
    		n = atoi(argv[1]);
    	}
    
    	for(i = 0; i < n; i++){  	   //出口1,父进程专用出口
    		if(fork() == 0)	　  	
    			break;  	   //出口2,子进程出口,i不自增
    	}
    
    	if(n == i){
    		sleep(i);
    		printf("parent. pid = %d\n", getpid());
    	}else {
    		sleep(i);
    		printf("%d child. pid = %d\n", i+1, getpid());
    	}
    
    	return 0;
    
    }
    
    /*akaedu@akaedu-G41MT-D3:~/lin/20140828_fock$ ./6
    1 child. pid = 7448
    2 child. pid = 7449
    3 child. pid = 7450
    4 child. pid = 7451
    5 child. pid = 7452
    parent. pid = 7447
    */

//父子进程共享打开的文件，建立的映射区
    //不共享：.data malloc stack heap 命令行参数　全局变量　
    #include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>
    
    int a = 100;
    
    int main(void)
    {
    	pid_t pid;
    	pid = fork();
    
    	if(pid == 0){	//sun
    		a = 2000;	//子进程修改了a值,父进程不共享修改
    		printf("child, a = %d\n", a);
    	} else {
    		sleep(1);	//保证sun先运行
    		printf("parent, a = %d\n", a);
    	}
    
    	return 0;
    }
    
    /*
    akaedu@akaedu-G41MT-D3:~/桌面/T74_system/0828_chp3_process_environ_control$ ./fork_shared 
    child, a = 2000
    parent, a = 100
    */

/＊＊＊＊推荐＊＊＊＊／
    /*
    父子进程映射区共享
    
    /dev/zero 是一个特殊的文件，当你读它的时候，它会提供无限的空字符(NULL, ASCII NUL, 0x00)。
    其中的一个典型用法是用它提供的字符流来覆盖信息，另一个常见用法是产生一个特定大小的空白文件。
    BSD就是通过mmap把/dev/zero映射到虚地址空间实现共享内存的。
    
    */
    #include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <fcntl.h>
    #include <sys/mman.h>
    
    #define N 4
    
    int main(void)
    {
    	int *p;
    	pid_t pid;
    
    	int fd = open("/dev/zero", O_RDWR);　
    
    	p = mmap(NULL, N, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
    	if(p == MAP_FAILED){		//注意:不是p == NULL
    		perror("mmap error");
    		exit(1);
    	}
    	close(fd);　　　		//映射完就可以关闭fd
    
    	pid = fork();				//创建子进程
    	if(pid == 0){
    		*p = 2000;
    		printf("child, *p = %d\n", *p);
    	} else {
    		sleep(1);
    		printf("parent, *p = %d\n", *p);
    	}
    
    	munmap(p, N);				//释放映射区
    
    	return 0;
    }
    
    /*akaedu@akaedu-G41MT-D3:~/桌面/T74_system/0828_chp3_process_environ_control$ ./fork_map_anon 
    child, *p = 2000
    parent, *p = 2000
    */
    <pre name="code" class="cpp">
    
    
    
    //父子进程共享打开的文件，建立的映射区 
    //方法较老，不推荐
    #include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <fcntl.h>
    #include <sys/mman.h>
    
    int var = 100;
    
    int main(void)
    {
    	int *p;
    	pid_t pid;
    
    	int fd;
    	fd = open("temp", O_RDWR|O_CREAT|O_TRUNC, 0644);
    	if(fd < 0){
    		perror("open error");
    		exit(1);
    	}
    	unlink("temp");				//删除临时文件目录项
    
    	lseek(fd, 3, SEEK_SET);		//open的文件长度0,不能直接建映射区
    	write(fd, "a", 1);			//引起IO操作，物理上拓展文件
    
    	p = (int *)mmap(NULL, 4, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
    	if(p == MAP_FAILED){		//注意:不是p == NULL
    		perror("mmap error");
    		exit(1);
    	}
    	close(fd);					//映射区建立完毕,即可关闭文件
    
    	pid = fork();				//创建子进程
    	if(pid == 0){
    		*p = 2000;
    		var = 1000;
    		printf("child, *p = %d, var = %d\n", *p, var);
    	} else {
    		sleep(1);
    		printf("parent, *p = %d, var = %d\n", *p, var);
    	}
    
    	munmap(p, 4);				//释放映射区
    
    	return 0;
    }
    
    /*akaedu@akaedu-G41MT-D3:~/桌面/T74_system/0828_chp3_process_environ_control$ ./fork_mmap 
    child, *p = 2000, var = 1000
    parent, *p = 1627389952, var = 100
    */