我已经为此挣扎了一段时间。我试图围绕运行子进程编写一个C++类。我正在使用fork()
,pipe()
,dup2()
和execv()
来启动子进程并将其stdout和stderr重定向到父级。据我所知,一切都可以正常工作,直到dup2()
被调用,并且在EINVAL
下失败(在macOS上,我认为这不是Linux中允许的错误类型)。如果删除管道周围的所有逻辑,则该类将按预期工作。
类声明:
class PosixSubprocess : public Subprocess {
std::string _cmd = {};
std::string _stdout = "";
std::string _stderr = "";
std::vector<std::string> _args = {};
long _pid = -1;
int _status = -1;
public:
void cmd(std::string val) override;
void addArg(std::string val) override;
void run() override;
int status() const override;
std::string out() const override;
std::string err() const override;
};
run()
的定义:void PosixSubprocess::run() {
std::array<int, 2> stdoutPipe = {};
std::array<int, 2> stderrPipe = {};
if (pipe(stdoutPipe.data()) < 0)
{
throw std::runtime_error("Subprocess: failed to create pipes. Errno: " + std::to_string(errno));
}
if (pipe(stderrPipe.data()) < 0)
{
throw std::runtime_error("Subprocess: failed to create pipes. Errno: " + std::to_string(errno));
}
_pid = fork();
if (_pid == 0) {
if (dup2(stderrPipe[1], STDERR_FILENO)) {
std::cout << "Subprocess: failed to redirect stderr. Errno " << errno << '\n';
exit(errno);
}
if (dup2(stdoutPipe[1], STDOUT_FILENO)) {
std::cout << "Subprocess: failed to redirect stdout. Errno " << errno << '\n';
exit(errno);
}
close(stdoutPipe[0]);
close(stdoutPipe[1]);
close(stderrPipe[0]);
close(stderrPipe[1]);
auto argv = std::make_unique<char*[]>(_args.size() + 1);
argv[_args.size()] = nullptr;
for (size_t i = 0; i < _args.size(); ++i) {
argv[i] = &(_args[i].front());
}
if(execvp(_cmd.c_str(), argv.get())) {
std::cerr << "Subprocess: failed to launch. Errno " << errno << '\n';
exit(errno);
}
} else if (_pid > 0) {
close(stdoutPipe[1]);
close(stderrPipe[1]);
std::array<char, 1024> buf;
auto appendPipe = [&buf](int fd, std::string& str) {
ssize_t nBytes = 0;
do {
nBytes = read(fd, buf.data(), buf.size());
str.append(buf.data(), nBytes);
if (nBytes) std::cout << nBytes << '\n';
} while (nBytes > 0);
};
while(!waitpid(_pid, &_status, WNOHANG)) {
appendPipe(stdoutPipe[0], _stdout);
appendPipe(stdoutPipe[0], _stderr);
}
} else {
close(stdoutPipe[0]);
close(stdoutPipe[1]);
close(stderrPipe[0]);
close(stderrPipe[1]);
throw std::runtime_error("Subprocess: fork failed.");
}
}
抱歉,这里没有代码,我可以肯定地说与该问题无关。
最佳答案
从 dup2
's manual page:
显然,由于dup2()
返回了原始文件被复制到的文件描述符,并且该文件描述符非零,因此所示代码认为这是一个错误。
错误条件由负返回值指示。