使用fork在进程的二叉树中进行广度优先搜索
我正在尝试使用c中的 fork（）构建一个包含四个级别的进程二叉树。
类似于：
我的目标是按顺序打印每个进程号（如广度优先搜索）例如：
输出
I'm the process 1 I'm the process 2 I'm the process 3 ... I'm the process 15
所以我写了这段代码：
#include <stdio.h>
#include <unistd.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
double last;
void new_tree(int);
int main(int narg, char * argv[]){
int n;
n = atoi(argv[1]);
last = pow(2,(n-1));
new_tree(1);
return 0;
}
void new_tree(int x){
char buff[60];
sprintf(buff, "Im the procces %d with pid %d and ppid %d\n",x,getpid(),getppid());
write(1,buff,strlen(buff));
if (x >= last)
return;
if (!fork()){
new_tree(2*x);
exit(0);
}
if(!fork()){
new_tree(2*x+1);
exit(0);
}
wait(NULL);
wait(NULL);
}
但是当我运行代码（./tree 4）时，我无法控制进程执行的顺序。我的输出有点正确但它仍然无序，因为有些进程在其他进程之前完成了同一级别。
任何人都可以帮我一个忙吗？
我的输出到现在为止：
Im the procces 1 Im the procces 3 Im the procces 2 Im the procces 6 Im the procces 7 Im the procces 5 Im the procces 13 Im the procces 15 Im the procces 4 Im the procces 8 Im the procces 14 Im the procces 12 Im the procces 11 Im the procces 10 Im the procces 9
每次执行时都会改变。
EDIT1： 我的代码可以创建进程的二叉树，但问题是按照我想要的顺序执行这些进程。
EDIT2： 我的输出有点不正确。我以为是，但我错了。
1 个答案:
答案 0 :(得分：0)
您的原始代码几乎在我的首选选项下干净利落地编译，这是一种恭维。我修改了它以将n初始化为4并在从if (narg == 2)计算n之前测试argv[1]，这可以防止程序在没有运行时崩溃参数。
该程序版本为ptree29.c。当使用参数3运行时，它按顺序生成结果，但是使用参数4（或无参数）或参数5，结果完全不按顺序排列：
$ ptree29 3
Im the procces 1 with pid 92986 and ppid 41763
Im the procces 2 with pid 92987 and ppid 92986
Im the procces 3 with pid 92988 and ppid 92986
Im the procces 4 with pid 92989 and ppid 92987
Im the procces 5 with pid 92991 and ppid 92987
Im the procces 6 with pid 92990 and ppid 92988
Im the procces 7 with pid 92992 and ppid 92988
$ ptree29 5
Im the procces 1 with pid 92993 and ppid 41763
Im the procces 2 with pid 92994 and ppid 92993
Im the procces 3 with pid 92995 and ppid 92993
Im the procces 4 with pid 92996 and ppid 92994
Im the procces 6 with pid 92997 and ppid 92995
Im the procces 5 with pid 92998 and ppid 92994
Im the procces 7 with pid 92999 and ppid 92995
Im the procces 8 with pid 93000 and ppid 92996
Im the procces 12 with pid 93001 and ppid 92997
Im the procces 10 with pid 93002 and ppid 92998
Im the procces 9 with pid 93003 and ppid 92996
Im the procces 13 with pid 93004 and ppid 92997
Im the procces 14 with pid 93005 and ppid 92999
Im the procces 11 with pid 93006 and ppid 92998
Im the procces 16 with pid 93007 and ppid 93000
Im the procces 24 with pid 93008 and ppid 93001
Im the procces 15 with pid 93009 and ppid 92999
Im the procces 25 with pid 93014 and ppid 93001
Im the procces 18 with pid 93011 and ppid 93003
Im the procces 28 with pid 93015 and ppid 93005
Im the procces 20 with pid 93010 and ppid 93002
Im the procces 26 with pid 93012 and ppid 93004
Im the procces 17 with pid 93013 and ppid 93000
Im the procces 22 with pid 93016 and ppid 93006
Im the procces 21 with pid 93017 and ppid 93002
Im the procces 30 with pid 93019 and ppid 93009
Im the procces 27 with pid 93018 and ppid 93004
Im the procces 19 with pid 93020 and ppid 93003
Im the procces 29 with pid 93021 and ppid 93005
Im the procces 23 with pid 93022 and ppid 93006
Im the procces 31 with pid 93023 and ppid 93009
$
您需要设计一种机制来控制进程打印“我是进程”消息的顺序。系统调用后，您已被授权使用（ fork()，wait()，waitpid()，fflush()，getpid()，getppid() ，pipe()，dup()，dup2()，read()，write()，close()，execl()，execv()，{ {1}}，execle()，execlp() ） - 我希望使用open()也不会成为一个停止 - 然后你可以创建一个文件包含打印其“我是进程”消息的最后一个进程的编号。每个进程都会等到它轮到它 - 它通过检查文件中的数字是否为数字减去1来知道。其他进程也可以读取该文件。当进程写出“我是进程”消息时，它会启动它的两个子节点，然后等待它们完成。
我选择使用我的execvp()和stderr.c代码（可从https://github.com/jleffler/soq/tree/master/src/libsoq获得Github），因为其中的函数（其名称都以stderr.h开头）使其变得微不足道使用PID和时间记录错误和消息，这在诸如此类的上下文中是非常宝贵的，同时有很多进程在运行。另一个优点是它提供单行错误处理，而不是每个错误3行或更多行，如果你没有这样的函数 - 这使我不太愿意编写错误处理代码。
代码也使用nanosleep()，这样如果一个进程读取的数字太小（或太大 - 但代码不处理该错误情况），它会在重试前休眠一毫秒。这足以限制重试率。
新代码位于err_的来源：
ptree17.c示例输出1 - 发送到/* SO 4574-5483 */
#include "stderr.h"
#include <fcntl.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>
static const char filename[] = "pt-next.dat";
static double last = 0.0;
static void new_tree(int num);
static void write_file(int num);
int main(int argc, char *argv[])
{
err_setarg0(argv[0]);
err_setlogopts(ERR_PID|ERR_MILLI);
int n = 4;
if (argc == 2)
n = atoi(argv[1]);
write_file(0);
last = pow(2, (n - 1));
new_tree(1);
return 0;
}
static void write_file(int num)
{
int fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0600);
if (fd < 0)
err_syserr("failed to create file '%s' for writing\n", filename);
if (write(fd, &num, sizeof(num)) != sizeof(num))
err_syserr("failed to write %d to file '%s'\n", num, filename);
close(fd);
err_remark("wrote %2d to '%s'\n", num, filename);
}
static int read_file(void)
{
int num = -1;
int fd = open(filename, O_RDONLY);
if (fd > 0)
{
if (read(fd, &num, sizeof(num)) != sizeof(num))
num = -1;
close(fd);
}
err_remark("read %2d from '%s'\n", num, filename);
return num;
}
static void wait_for_turn(int num)
{
struct timespec ms = { .tv_sec = 0, .tv_nsec = 1000000 };
while (read_file() != num - 1)
{
err_remark("dozing\n");
nanosleep(&ms, 0);
}
}
static void new_tree(int x)
{
char buff[60];
err_remark("Process = %2d\n", x);
wait_for_turn(x);
sprintf(buff, "I'm process %2d with pid %5d and ppid %5d\n", x, getpid(), getppid());
write(1, buff, strlen(buff));
write_file(x);
if (x >= last)
return;
if (!fork())
{
new_tree(2 * x);
exit(0);
}
if (!fork())
{
new_tree(2 * x + 1);
exit(0);
}
int corpse, status;
while ((corpse = wait(&status)) > 0)
err_remark("child %5d exited with status 0x%.4X\n", corpse, status);
}
的错误：
/dev/null示例输出2 - 标准错误可见：
$ ptree17 5 2>/dev/null
I'm process 1 with pid 93174 and ppid 41763
I'm process 2 with pid 93175 and ppid 93174
I'm process 3 with pid 93176 and ppid 93174
I'm process 4 with pid 93177 and ppid 93175
I'm process 5 with pid 93178 and ppid 93175
I'm process 6 with pid 93179 and ppid 93176
I'm process 7 with pid 93180 and ppid 93176
I'm process 8 with pid 93181 and ppid 93177
I'm process 9 with pid 93182 and ppid 93177
I'm process 10 with pid 93183 and ppid 93178
I'm process 11 with pid 93184 and ppid 93178
I'm process 12 with pid 93185 and ppid 93179
I'm process 13 with pid 93186 and ppid 93179
I'm process 14 with pid 93187 and ppid 93180
I'm process 15 with pid 93188 and ppid 93180
I'm process 16 with pid 93189 and ppid 93181
I'm process 17 with pid 93190 and ppid 93181
I'm process 18 with pid 93191 and ppid 93182
I'm process 19 with pid 93192 and ppid 93182
I'm process 20 with pid 93193 and ppid 93183
I'm process 21 with pid 93194 and ppid 93183
I'm process 22 with pid 93195 and ppid 93184
I'm process 23 with pid 93196 and ppid 93184
I'm process 24 with pid 93197 and ppid 93185
I'm process 25 with pid 93198 and ppid 93185
I'm process 26 with pid 93199 and ppid 93186
I'm process 27 with pid 93200 and ppid 93186
I'm process 28 with pid 93201 and ppid 93187
I'm process 29 with pid 93203 and ppid 93187
I'm process 30 with pid 93202 and ppid 93188
I'm process 31 with pid 93204 and ppid 93188
$
正如您所看到的，“我是过程”消息是严格按顺序打印的。并且整个程序运行不需要很长时间 - 从第一个到最后一个打印的消息总共大约19毫秒。
$ ptree17
ptree17: 2017-08-17 20:03:20.798 - pid=93210: wrote 0 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.799 - pid=93210: Process = 1
ptree17: 2017-08-17 20:03:20.799 - pid=93210: read 0 from 'pt-next.dat'
I'm process 1 with pid 93210 and ppid 41763
ptree17: 2017-08-17 20:03:20.800 - pid=93210: wrote 1 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.801 - pid=93211: Process = 2
ptree17: 2017-08-17 20:03:20.801 - pid=93211: read 1 from 'pt-next.dat'
I'm process 2 with pid 93211 and ppid 93210
ptree17: 2017-08-17 20:03:20.801 - pid=93212: Process = 3
ptree17: 2017-08-17 20:03:20.801 - pid=93212: read -1 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.801 - pid=93212: dozing
ptree17: 2017-08-17 20:03:20.804 - pid=93211: wrote 2 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.804 - pid=93212: read 2 from 'pt-next.dat'
I'm process 3 with pid 93212 and ppid 93210
ptree17: 2017-08-17 20:03:20.804 - pid=93212: wrote 3 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.804 - pid=93213: Process = 4
ptree17: 2017-08-17 20:03:20.805 - pid=93213: read 3 from 'pt-next.dat'
I'm process 4 with pid 93213 and ppid 93211
ptree17: 2017-08-17 20:03:20.805 - pid=93214: Process = 6
ptree17: 2017-08-17 20:03:20.805 - pid=93215: Process = 5
ptree17: 2017-08-17 20:03:20.805 - pid=93216: Process = 7
ptree17: 2017-08-17 20:03:20.805 - pid=93213: wrote 4 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.805 - pid=93216: read 4 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.805 - pid=93214: read 4 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.805 - pid=93215: read 4 from 'pt-next.dat'
I'm process 5 with pid 93215 and ppid 93211
ptree17: 2017-08-17 20:03:20.805 - pid=93216: dozing
ptree17: 2017-08-17 20:03:20.805 - pid=93214: dozing
ptree17: 2017-08-17 20:03:20.805 - pid=93215: wrote 5 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.806 - pid=93217: Process = 8
ptree17: 2017-08-17 20:03:20.806 - pid=93217: read 5 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.806 - pid=93217: dozing
ptree17: 2017-08-17 20:03:20.806 - pid=93218: Process = 9
ptree17: 2017-08-17 20:03:20.806 - pid=93219: Process = 10
ptree17: 2017-08-17 20:03:20.806 - pid=93219: read 5 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.806 - pid=93218: read 5 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.806 - pid=93219: dozing
ptree17: 2017-08-17 20:03:20.806 - pid=93218: dozing
ptree17: 2017-08-17 20:03:20.806 - pid=93220: Process = 11
ptree17: 2017-08-17 20:03:20.806 - pid=93220: read 5 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.806 - pid=93216: read 5 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.806 - pid=93220: dozing
ptree17: 2017-08-17 20:03:20.806 - pid=93216: dozing
ptree17: 2017-08-17 20:03:20.806 - pid=93214: read 5 from 'pt-next.dat'
I'm process 6 with pid 93214 and ppid 93212
ptree17: 2017-08-17 20:03:20.807 - pid=93214: wrote 6 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.807 - pid=93217: read 6 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.807 - pid=93217: dozing
ptree17: 2017-08-17 20:03:20.807 - pid=93218: read 6 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.807 - pid=93219: read 6 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.807 - pid=93218: dozing
ptree17: 2017-08-17 20:03:20.807 - pid=93221: Process = 12
ptree17: 2017-08-17 20:03:20.807 - pid=93219: dozing
ptree17: 2017-08-17 20:03:20.808 - pid=93221: read 6 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.808 - pid=93220: read 6 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.808 - pid=93221: dozing
ptree17: 2017-08-17 20:03:20.808 - pid=93220: dozing
ptree17: 2017-08-17 20:03:20.808 - pid=93222: Process = 13
ptree17: 2017-08-17 20:03:20.808 - pid=93216: read 6 from 'pt-next.dat'
I'm process 7 with pid 93216 and ppid 93212
ptree17: 2017-08-17 20:03:20.808 - pid=93222: read 6 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.808 - pid=93222: dozing
ptree17: 2017-08-17 20:03:20.808 - pid=93216: wrote 7 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.808 - pid=93217: read 7 from 'pt-next.dat'
I'm process 8 with pid 93217 and ppid 93213
ptree17: 2017-08-17 20:03:20.809 - pid=93217: wrote 8 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.809 - pid=93218: read 8 from 'pt-next.dat'
I'm process 9 with pid 93218 and ppid 93213
ptree17: 2017-08-17 20:03:20.809 - pid=93223: Process = 14
ptree17: 2017-08-17 20:03:20.809 - pid=93218: wrote 9 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.809 - pid=93223: read -1 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.809 - pid=93219: read 8 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.809 - pid=93221: read 9 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.809 - pid=93224: Process = 15
ptree17: 2017-08-17 20:03:20.809 - pid=93223: dozing
ptree17: 2017-08-17 20:03:20.809 - pid=93219: dozing
ptree17: 2017-08-17 20:03:20.809 - pid=93213: child 93217 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.809 - pid=93222: read 9 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.809 - pid=93224: read 9 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.809 - pid=93220: read 9 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.809 - pid=93221: dozing
ptree17: 2017-08-17 20:03:20.809 - pid=93224: dozing
ptree17: 2017-08-17 20:03:20.809 - pid=93222: dozing
ptree17: 2017-08-17 20:03:20.810 - pid=93220: dozing
ptree17: 2017-08-17 20:03:20.810 - pid=93213: child 93218 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.810 - pid=93211: child 93213 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.810 - pid=93223: read 9 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.810 - pid=93219: read 9 from 'pt-next.dat'
I'm process 10 with pid 93219 and ppid 93215
ptree17: 2017-08-17 20:03:20.811 - pid=93223: dozing
ptree17: 2017-08-17 20:03:20.811 - pid=93219: wrote 10 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.811 - pid=93224: read 10 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.811 - pid=93222: read 10 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.811 - pid=93220: read 10 from 'pt-next.dat'
I'm process 11 with pid 93220 and ppid 93215
ptree17: 2017-08-17 20:03:20.811 - pid=93221: read 10 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.811 - pid=93224: dozing
ptree17: 2017-08-17 20:03:20.811 - pid=93221: dozing
ptree17: 2017-08-17 20:03:20.811 - pid=93222: dozing
ptree17: 2017-08-17 20:03:20.812 - pid=93220: wrote 11 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.812 - pid=93215: child 93219 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.812 - pid=93223: read 11 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.812 - pid=93223: dozing
ptree17: 2017-08-17 20:03:20.812 - pid=93215: child 93220 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.812 - pid=93211: child 93215 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.813 - pid=93210: child 93211 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.813 - pid=93222: read 11 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.813 - pid=93224: read 11 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.813 - pid=93222: dozing
ptree17: 2017-08-17 20:03:20.813 - pid=93224: dozing
ptree17: 2017-08-17 20:03:20.813 - pid=93221: read 11 from 'pt-next.dat'
I'm process 12 with pid 93221 and ppid 93214
ptree17: 2017-08-17 20:03:20.813 - pid=93221: wrote 12 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.813 - pid=93223: read 12 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.813 - pid=93223: dozing
ptree17: 2017-08-17 20:03:20.814 - pid=93214: child 93221 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.814 - pid=93222: read 12 from 'pt-next.dat'
I'm process 13 with pid 93222 and ppid 93214
ptree17: 2017-08-17 20:03:20.815 - pid=93222: wrote 13 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.815 - pid=93224: read 13 from 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.815 - pid=93223: read 13 from 'pt-next.dat'
I'm process 14 with pid 93223 and ppid 93216
ptree17: 2017-08-17 20:03:20.815 - pid=93224: dozing
ptree17: 2017-08-17 20:03:20.815 - pid=93214: child 93222 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.815 - pid=93212: child 93214 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.816 - pid=93223: wrote 14 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.816 - pid=93224: read 14 from 'pt-next.dat'
I'm process 15 with pid 93224 and ppid 93216
ptree17: 2017-08-17 20:03:20.816 - pid=93216: child 93223 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.816 - pid=93224: wrote 15 to 'pt-next.dat'
ptree17: 2017-08-17 20:03:20.817 - pid=93216: child 93224 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.817 - pid=93212: child 93216 exited with status 0x0000
ptree17: 2017-08-17 20:03:20.817 - pid=93210: child 93212 exited with status 0x0000
$
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