我在分配作业时遇到问题。我正在尝试执行3个并发进程(在C ++中),其中2个是Python程序,其中1个是C ++程序。
我的C ++程序(sample.cpp):
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <string>
#include <stdlib.h>
#include <iostream>
#include <vector>
#include <signal.h>
using namespace std;
int main()
{
while (true)
{
cout << "lol" << endl;
sleep(2);
}
return 0;
}
我的Python程序1(sample.py):
import sys
while True:
line = sys.stdin.readline().strip()
print "Python says: " + str(line)
我的Python程序2(sample2.py):
import sys
while True:
line = sys.stdin.readline().strip()
print "Python 2 says: " + str(line)
这是我的驱动程序C ++程序,用于分叉进程:
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <string>
#include <stdlib.h>
#include <iostream>
#include <vector>
#include <signal.h>
using namespace std;
int main()
{
vector<pid_t> kids;
int fd[2];
if (pipe(fd) < 0)
{
cout << "Error";
return 1;
}
int fd2[2];
if (pipe(fd2) < 0)
{
cout << "Error";
return 1;
}
pid_t pid;
pid = fork();
if (pid == 0)
{
dup2(fd[1], STDOUT_FILENO);
close(fd[1]);
close(fd[0]);
while (true)
{
execvp("./sample", NULL);
}
}
else
{
kids.push_back(pid);
pid = fork();
if (pid == 0)
{
dup2(fd[0], STDIN_FILENO);
close(fd[0]);
close(fd[1]);
dup2(fd2[1], STDOUT_FILENO);
close(fd2[1]);
close(fd2[0]);
char * python = "/usr/bin/python";
char * pythonProgram = "./sample.py";
char * pythonArgs[] = {python, pythonProgram, NULL, NULL};
execvp(python, pythonArgs);
}
else
{
kids.push_back(pid);
pid = fork();
if (pid == 0)
{
dup2(fd2[0], STDIN_FILENO);
close(fd2[0]);
close(fd2[1]);
char * python = "/usr/bin/python";
char * pythonProgram = "./sample2.py";
char * pythonArgs[] = {python, pythonProgram, NULL, NULL};
execvp(python, pythonArgs);
}
else
{
kids.push_back(pid);
}
}
}
close(fd[0]);
close(fd[1]);
close(fd2[0]);
close(fd2[1]);
for (pid_t k : kids)
{
int status;
//kill (k, SIGTERM);
waitpid(k, &status, 0);
}
}
当我运行该程序时,应该会看到“ Python 2说:Python说:大声笑”。但是,我什么也没看到(完全空白)...它只是挂起。我究竟做错了什么?我尝试查找很多东西,但没有运气。
答案 0 :(得分:1)
除非您期望execvp失败,否则围绕./sample开头的while循环是没有意义的。成功调用exec *将永远不会返回。实际对execvp的调用也是错误的:
execvp("./sample", NULL);
第二个参数应为char *const[]
。
您应该为execvp:s添加错误处理(如带有std::exit(1)
的行)。否则,如果execvp失败,您将在程序的主流程中运行子进程。
python程序需要无缓冲运行,否则消息将花费很长时间显示。您还应该检查读取行是否成功。
sample.py
import sys
while True:
line = sys.stdin.readline().strip()
if not line: break
print "Python says: " + str(line)
sample2.py
import sys
while True:
line = sys.stdin.readline().strip()
if not line: break
print "Python 2 says: " + str(line)
driver.cpp
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <string>
#include <stdlib.h>
#include <iostream>
#include <vector>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
using namespace std;
int main()
{
vector<pid_t> kids;
int fd[2];
if (pipe(fd)==-1)
{
clog << "Error\n";
return 1;
}
int fd2[2];
if (pipe(fd2)==-1)
{
clog << "Error\n";
return 1;
}
pid_t pid;
pid = fork();
if (pid == 0)
{
dup2(fd[1], STDOUT_FILENO);
close(fd[1]);
close(fd[0]);
char* const args[] = { NULL };
execvp("./sample", args);
std::clog << "sample failed\n";
std::exit(1);
}
else
{
kids.push_back(pid);
pid = fork();
if (pid == 0)
{
dup2(fd[0], STDIN_FILENO);
close(fd[0]);
close(fd[1]);
dup2(fd2[1], STDOUT_FILENO);
close(fd2[1]);
close(fd2[0]);
char const* python = "/usr/bin/python";
char const* pythonProgram = "./sample.py";
char const* pythonArgs[] = {python, "-u", pythonProgram, NULL};
execvp(python, const_cast<char* const*>(pythonArgs));
std::clog << "sample.py failed\n";
std::exit(1);
}
else
{
kids.push_back(pid);
pid = fork();
if (pid == 0)
{
dup2(fd2[0], STDIN_FILENO);
close(fd2[0]);
close(fd2[1]);
char const* python = "/usr/bin/python";
char const* pythonProgram = "./sample2.py";
char const* pythonArgs[] = {python, "-u", pythonProgram, NULL};
execvp(python, const_cast<char* const*>(pythonArgs));
std::clog << "sample2.py failed\n";
std::exit(1);
}
else
{
kids.push_back(pid);
}
}
}
close(fd[0]);
close(fd[1]);
close(fd2[0]);
close(fd2[1]);
for (pid_t k : kids)
{
int status;
//kill (k, SIGTERM);
waitpid(k, &status, 0);
}
}