深入浅出fork()

以你之姓@ 2022-07-03 15:25 102阅读 0赞

先看一个简单的例子1:

#include <stdio.h>
    #include <sys/types.h>
    int main()
    {
    	pid_t pid;
    	int i;
    	char *str = "hello!";
        for (i = 0; i<2; i++) {
    		if ((pid = fork()) < 0) {
    			perror("fork");
    			return -1;
    		} 
    		else if (pid == 0) {	// child
    			printf("in child process pid,parent pid:%d\n", getpid(), getppid());	
    		}
    		else {					//parent
    			printf("in parent process pid:%d, child pid:%d\n", getpid(), pid);
    			return 0;	
    		}	
    		
    		printf("%s,%d\n", str, getpid());
    	}
    
    	return 0;
    }

结果:

in child process pid:4305,parent pid:4304  
hello!,4305  
in child process pid:4306,parent pid:4305  
hello!,4306  
in parent process pid:4305, child pid:4306  
in parent process pid:4304, child pid:4305

再看一个例子2,仅去掉了父进程当中的return 0;语句:

#include <stdio.h>
    #include <sys/types.h>
    int main()
    {
    	pid_t pid;
    	int i;
    	char *str = "hello!";
        for (i = 0; i<2; i++) {
    		if ((pid = fork()) < 0) {
    			perror("fork");
    			return -1;
    		} 
    		else if (pid == 0) {	// child
    			printf("in child process pid,parent pid:%d\n", getpid(), getppid());	
    		}
    		else {					//parent
    			printf("in parent process pid:%d, child pid:%d\n", getpid(), pid);
    			//return 0;	
    		}	
    		
    		printf("%s,%d\n", str, getpid());
    	}
    
    	return 0;
    }

结果:

in child process pid:4331,parent pid:4330  
hello!,4331  
in child process pid:4332,parent pid:4331  
hello!,4332  
in parent process pid:4331, child pid:4332  
hello!,4331  
in parent process pid:4330, child pid:4331  
hello!,4330  
in child process pid:4333,parent pid:4330  
hello!,4333  
in parent process pid:4330, child pid:4333  
hello!,4330

结合两个小例子的结果,自己分析一下,应该对父子进程资源共享有个大概的体验了吧.例1会产生2个子进程,例2会产生2^2-1个子进程.也就是说,如果父子进程中没有一个在for环循中退出去,那么如果有N次环循,会产生2^N-1个子进程(当然这些子进程中,只有N个是根父进程的子进程,其它的是子进程产生的子进程)