【发布时间】：2020-04-14 07:38:32
【问题描述】：
有一个使用boost::asio::io_context的简单例子
https://github.com/unegare/boost-ex/blob/500e46f4d3b41e2abe48e2deccfab39d44ae94e0/main.cpp
#include <boost/asio.hpp>
#include <boost/beast/core.hpp>
#include <boost/beast/http.hpp>
#include <boost/beast/version.hpp>
#include <thread>
#include <vector>
#include <memory>
#include <mutex>
#include <chrono>
#include <iostream>
#include <exception>
std::mutex m_stdout;
class MyWorker {
std::shared_ptr<boost::asio::io_context> io_context;
std::shared_ptr<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> work_guard;
public:
MyWorker(std::shared_ptr<boost::asio::io_context> &_io_context, std::shared_ptr<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> &_work_guard):
io_context(_io_context), work_guard(_work_guard) {}
MyWorker(const MyWorker &mw): io_context(mw.io_context), work_guard(mw.work_guard) {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] MyWorker copy constructor" << std::endl;
m_stdout.unlock();
}
MyWorker(MyWorker &&mw): io_context(std::move(mw.io_context)), work_guard(std::move(mw.work_guard)) {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] MyWorker move constructor" << std::endl;
m_stdout.unlock();
}
~MyWorker() {}
void operator() () {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] Thread Start" << std::endl;
m_stdout.unlock();
while(true) {
try {
boost::system::error_code ec;
io_context->run(ec);
if (ec) {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] MyWorker: received an error: " << ec << std::endl;
m_stdout.unlock();
continue;
}
break;
} catch (std::exception &ex) {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] MyWorker: caught an exception: " << ex.what() << std::endl;
m_stdout.unlock();
}
}
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] Thread Finish" << std::endl;
m_stdout.unlock();
}
};
class Client: public std::enable_shared_from_this<Client> {
std::shared_ptr<boost::asio::io_context> io_context;
std::shared_ptr<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> work_guard;
std::shared_ptr<boost::asio::ip::tcp::socket> sock;
std::shared_ptr<std::array<char, 512>> buff;
public:
Client(std::shared_ptr<boost::asio::io_context> &_io_context, std::shared_ptr<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> &_work_guard, std::shared_ptr<boost::asio::ip::tcp::socket> &_sock):
io_context(_io_context), work_guard(_work_guard), sock(_sock) {
buff = std::make_shared<std::array<char,512>>();
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << " with args" << std::endl;
m_stdout.unlock();
}
Client(const Client &cl): io_context(cl.io_context), work_guard(cl.work_guard), sock(cl.sock), buff(cl.buff) {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << " copy" << std::endl;
m_stdout.unlock();
}
Client(Client &&cl): io_context(std::move(cl.io_context)), work_guard(std::move(cl.work_guard)), sock(std::move(cl.sock)), buff(std::move(cl.buff)) {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << " move" << std::endl;
m_stdout.unlock();
}
~Client() {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << " buff.use_count: " << buff.use_count() << " | sock.use_count: " << sock.use_count() << " | io_context.use_count: " << io_context.use_count() << std::endl;
m_stdout.unlock();
}
void OnConnect(const boost::system::error_code &ec) {
std::cout << __FUNCTION__ << std::endl;
if (ec) {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << ": " << ec << std::endl;
m_stdout.unlock();
} else {
// buff = std::make_shared<std::array<char, 512>>();
char req[] = "GET / HTTP/1.1\r\nHost: unegare.info\r\n\r\n";
memcpy(buff->data(), req, strlen(req));
m_stdout.lock();
std::cout << req << std::endl;
m_stdout.unlock();
sock->async_write_some(boost::asio::buffer(buff->data(), strlen(buff->data())), std::bind(std::mem_fn(&Client::OnSend), this, std::placeholders::_1, std::placeholders::_2));
}
std::cout << __FUNCTION__ << " use_count: " << buff.use_count() << std::endl;
}
void OnSend(const boost::system::error_code &ec, std::size_t bytes_transferred) {
std::cout << __FUNCTION__ << " use_count: " << io_context.use_count() << std::endl;
if (ec) {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << ": " << ec << std::endl;
m_stdout.unlock();
} else {
std::cout << __FUNCTION__ << " use_count: " << buff.use_count() << std::endl;
buff->fill(0);
std::cout << __FUNCTION__ << std::endl;
sock->async_read_some(boost::asio::buffer(buff->data(), buff->size()), std::bind(std::mem_fn(&Client::OnRecv), this, std::placeholders::_1, std::placeholders::_2));
}
}
void OnRecv(const boost::system::error_code &ec, std::size_t bytes_transferred) {
std::cout << __FUNCTION__ << std::endl;
if (ec) {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << ": " << ec << std::endl;
m_stdout.unlock();
} else {
m_stdout.lock();
std::cout << buff->data() << std::endl;
m_stdout.unlock();
}
}
};
int main () {
std::shared_ptr<boost::asio::io_context> io_context(std::make_shared<boost::asio::io_context>());
std::shared_ptr<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> work_guard(
std::make_shared<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> (boost::asio::make_work_guard(*io_context))
);
MyWorker mw(io_context, work_guard);
std::vector<std::thread> vth;
vth.reserve(1);
for (int i = 1; i > 0; --i) {
vth.emplace_back(mw);
}
std::shared_ptr<Client> cl = 0;
try {
boost::asio::ip::tcp::resolver resolver(*io_context);
boost::asio::ip::tcp::resolver::query query("unegare.info", "80");
boost::asio::ip::tcp::endpoint ep = *resolver.resolve(query);
m_stdout.lock();
std::cout << "ep: " << ep << std::endl;
m_stdout.unlock();
std::shared_ptr<boost::asio::ip::tcp::socket> sock(std::make_shared<boost::asio::ip::tcp::socket>(*io_context));
std::shared_ptr<Client> cl2(std::make_shared<Client>(io_context, work_guard, sock));
cl = cl2->shared_from_this();
m_stdout.lock();
std::cout << "HERE: use_count = " << cl.use_count() << std::endl;
m_stdout.unlock();
sock->async_connect(ep, std::bind(std::mem_fn(&Client::OnConnect), *cl2->shared_from_this(), std::placeholders::_1));
std::this_thread::sleep_for(std::chrono::duration<double>(1));
m_stdout.lock();
std::cout << "AFTER CALL" << std::endl;
m_stdout.unlock();
// asm volatile ("");
} catch (std::exception &ex) {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] Main Thread: caught an exception: " << ex.what() << std::endl;
m_stdout.unlock();
}
try {
char t;
std::cin >> t;
work_guard->reset();
// std::this_thread::sleep_for(std::chrono::duration<double>(1));
// std::cout << "Running" << std::endl;
// io_context->run();
} catch (std::exception &ex) {
m_stdout.lock();
std::cout << "[" << std::this_thread::get_id() << "] Main Thread: caught an exception: " << ex.what() << std::endl;
m_stdout.unlock();
}
std::for_each(vth.begin(), vth.end(), std::mem_fn(&std::thread::join));
return 0;
}
标准输出：
[140487203505984] MyWorker copy constructor
[140487203505984] MyWorker move constructor
[140487185372928] Thread Start
ep: 95.165.130.37:80
[140487203505984] Client with args
HERE: use_count = 2
[140487203505984] Client copy
[140487203505984] Client move
[140487203505984] ~Client buff.use_count: 0 | sock.use_count: 0 | io_context.use_count: 0
[140487185372928] Client move
[140487185372928] ~Client buff.use_count: 0 | sock.use_count: 0 | io_context.use_count: 0
OnConnect
GET / HTTP/1.1
Host: unegare.info
OnConnect use_count: 2
[140487185372928] ~Client buff.use_count: 2 | sock.use_count: 3 | io_context.use_count: 5
Segmentation Fault (core dumped)
但是对Client对象的引用错误导致的segfault理解有点问题。
但我不明白为什么cl2在调用后会被破坏
sock->async_connect(ep, std::bind(std::mem_fn(&Client::OnConnect), *cl2->shared_from_this(), std::placeholders::_1));
在 162 行。
还有……为什么要调用复制构造函数？
从上面的stdout 可以看出。
【问题讨论】：
-
请发布一个完整的示例来重现该问题。根据您的描述，我猜测为调用
bind()创建的函数对象复制了相关对象。 -
@DietmarKühl 在主题第一行的链接中有一个完整的示例。只有一个文件。
-
此链接可能会更改，从而使问题/答案变得毫无价值。因此，问题需要在这里完成。
-
这不是一个真正的简单示例。
标签： c++ c++11 boost boost-asio shared-ptr