我在代码中发现了这个奇怪的错误。这是我自己设定的测试案例。
#include <memory>
#include <thread>
#include <stack>
#include <system_error>
#include <boost/asio.hpp>
using boost::asio::io_service;
using std::placeholders::_1;
class async_service
{
public:
async_service();
async_service(size_t number_threads);
~async_service();
async_service(const async_service&) = delete;
void operator=(const async_service&) = delete;
void spawn();
void shutdown();
io_service& get_service();
const io_service& get_service() const;
private:
io_service service_;
io_service::work* work_;
std::vector<std::thread> threads_;
};
async_service::async_service()
: work_(nullptr)
{
}
async_service::async_service(size_t number_threads)
: work_(nullptr)
{
for (size_t i = 0; i < number_threads; ++i)
spawn();
}
async_service::~async_service()
{
std::cout << __PRETTY_FUNCTION__ << std::endl;
service_.stop();
for (std::thread& t: threads_)
t.join();
}
void run_service(io_service* service)
{
service->run();
}
void async_service::spawn()
{
if (!work_)
work_ = new io_service::work(service_);
threads_.push_back(std::thread(run_service, &service_));
}
void async_service::shutdown()
{
delete work_;
work_ = nullptr;
}
io_service& async_service::get_service()
{
return service_;
}
const io_service& async_service::get_service() const
{
return service_;
}
// --------------------------------------------------------------
template <typename... Args>
class subscriber
: public std::enable_shared_from_this<subscriber<Args...>>
{
public:
typedef std::function<void (Args...)> handler_type;
typedef std::shared_ptr<subscriber<Args...>> ptr;
subscriber(async_service& service)
: strand_(service.get_service())
{
}
void subscribe(handler_type handle)
{
strand_.dispatch(
std::bind(&subscriber<Args...>::do_subscribe,
this->shared_from_this(), handle));
}
void relay(Args... params)
{
strand_.dispatch(
std::bind(&subscriber<Args...>::do_relay,
this->shared_from_this(), std::forward<Args>(params)...));
}
private:
typedef std::stack<handler_type> registry_stack;
void do_subscribe(handler_type handle)
{
registry_.push(handle);
}
void do_relay(Args... params)
{
registry_stack notify_copy = std::move(registry_);
registry_ = registry_stack();
while (!notify_copy.empty())
{
notify_copy.top()(params...);
notify_copy.pop();
}
assert(notify_copy.empty());
}
io_service::strand strand_;
registry_stack registry_;
};
// --------------------------------------------------------
class lala_channel_proxy
: public std::enable_shared_from_this<lala_channel_proxy>
{
public:
typedef std::function<void (const std::error_code&)> receive_inventory_handler;
lala_channel_proxy(async_service& service)
: strand_(service.get_service())
{
inventory_subscriber_ =
std::make_shared<inventory_subscriber_type>(service);
}
void start()
{
read_header();
}
void subscribe_inventory(receive_inventory_handler handle_receive)
{
inventory_subscriber_->subscribe(handle_receive);
}
typedef subscriber<const std::error_code&> inventory_subscriber_type;
void read_header()
{
strand_.post(
std::bind(&lala_channel_proxy::handle_read_header,
shared_from_this(), boost::system::error_code(), 0));
}
void handle_read_header(const boost::system::error_code& ec,
size_t bytes_transferred)
{
std::cout << "inventory ----------" << std::endl;
inventory_subscriber_->relay(std::error_code());
sleep(1.0);
read_header();
}
io_service::strand strand_;
inventory_subscriber_type::ptr inventory_subscriber_;
};
typedef std::shared_ptr<lala_channel_proxy> lala_channel_proxy_ptr;
class lala_channel
{
public:
lala_channel(async_service& service)
{
lala_channel_proxy_ptr proxy =
std::make_shared<lala_channel_proxy>(service);
proxy->start();
//weak_proxy_ = proxy;
strong_proxy_ = proxy;
}
void subscribe_inventory(
lala_channel_proxy::receive_inventory_handler handle_receive)
{
lala_channel_proxy_ptr proxy = strong_proxy_;
proxy->subscribe_inventory(handle_receive);
}
lala_channel_proxy_ptr strong_proxy_;
// Normally this has a weak pointer to the channel pimpl to allow
// it to die, but whether it uses a weak_ptr or shared_ptr makes
// no difference.
//std::weak_ptr<channel_proxy> weak_proxy_;
};
typedef std::shared_ptr<lala_channel> lala_channel_ptr;
//typedef lala_channel_proxy_ptr lala_channel_ptr;
class session
: public std::enable_shared_from_this<session>
{
public:
typedef std::function<void (const std::error_code&)> completion_handler;
session(async_service& service, async_service& mempool_service,
async_service& disk_service)
: strand_(service.get_service()),
txpool_strand_(mempool_service.get_service()),
chain_strand_(disk_service.get_service()), service_(service)
{
}
void start()
{
auto this_ptr = shared_from_this();
lala_channel_ptr node =
std::make_shared<lala_channel>(service_);
node->subscribe_inventory(
std::bind(&session::inventory, this_ptr, _1, node));
for (size_t i = 0; i < 500; ++i)
{
chain_strand_.post(
[]()
{
std::cout << "HERE!" << std::endl;
sleep(2);
});
}
}
private:
void inventory(const std::error_code& ec, lala_channel_ptr node)
{
if (ec)
{
std::cerr << ec.message() << std::endl;
return;
}
auto this_ptr = shared_from_this();
txpool_strand_.post([]() {});
node->subscribe_inventory(
std::bind(&session::inventory, this_ptr, _1, node));
}
async_service& service_;
io_service::strand txpool_strand_, strand_, chain_strand_;
};
int main()
{
// First level
{
// Bug only happens for this ordering of async_service's
// That means it is only triggered when they are destroyed in
// this reverse order.
async_service network_service(1), disk_service(1), mempool_service(1);
//async_service network_service(1), mempool_service(1), disk_service(1);
//async_service disk_service(1), mempool_service(1), network_service(1);
//async_service disk_service(1), network_service(1), mempool_service(1);
//async_service mempool_service(1), disk_service(1), network_service(1);
//async_service mempool_service(1), network_service(1), disk_service(1);
// Second level
{
// Should be kept alive by io_service
auto s = std::make_shared<session>(network_service, mempool_service, disk_service);
s->start();
}
//network_service.shutdown();
//disk_service.shutdown();
//mempool_service.shutdown();
sleep(3);
// Never gets past here
}
std::cout << "Exiting..." << std::endl;
return 0;
}
当我运行它时，我明白了：
$ g++ -std=c++0x /tmp/ideone_y6OlI.cpp -lboost_system -pthread -ggdb
$ gdb a.out
GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2) 7.4-2012.04
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://bugs.launchpad.net/gdb-linaro/>...
Reading symbols from /home/genjix/src/brokenlibbtc/a.out...done.
(gdb) r
Starting program: /home/genjix/src/brokenlibbtc/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7ffff6deb700 (LWP 28098)]
[New Thread 0x7ffff65ea700 (LWP 28099)]
[New Thread 0x7ffff5de9700 (LWP 28100)]
inventory ----------
HERE!
inventory ----------
HERE!
inventory ----------
async_service::~async_service()
async_service::~async_service()
[Thread 0x7ffff5de9700 (LWP 28100) exited]
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff6deb700 (LWP 28098)]
0x0000000000405873 in boost::asio::detail::task_io_service::wake_one_idle_thread_and_unlock (this=0x6255e0, lock=...) at /usr/include/boost/asio/detail/impl/task_io_service.ipp:461
461 first_idle_thread_ = idle_thread->next;
与1.48和1.49相同。
我想知道为什么会这样。它只发生在这种高度特殊的配置中。如果我改变了什么，那么就不会发生错误。
async_service是io_service的便利包装器。奇怪的是，如果我将io_service更改为* io_service并且不删除io_service，那么错误就不会发生......但是这肯定不重要吗？
如果查看main（）中的源代码，则会创建3个async_service对象。他们每个人都管理一个io_service的生命周期。
// Bug only happens for this ordering of async_service's
// That means it is only triggered when they are destroyed in
// this reverse order.
async_service network_service(1), disk_service(1), mempool_service(1);
//async_service network_service(1), mempool_service(1), disk_service(1);
//async_service disk_service(1), mempool_service(1), network_service(1);
//async_service disk_service(1), network_service(1), mempool_service(1);
//async_service mempool_service(1), disk_service(1), network_service(1);
//async_service mempool_service(1), network_service(1), disk_service(1);
订阅者类表示特定事件的订阅...调用事物。会话和频道的内容是根据较大的节目改编的，因此它们可能看起来很混乱/混乱。
答案 0 :(得分：3)
一个问题是session::inventory，当从构造函数的第一个参数（在失败的情况下为network_service）下的线程执行时，尝试访问使用第二个参数初始化的链（{ {1}}）。
mempool_service鉴于破坏的顺序，void inventory(const std::error_code& ec, lala_channel_ptr node)
{
if (ec)
{
std::cerr << ec.message() << std::endl;
return;
}
auto this_ptr = shared_from_this();
txpool_strand_.post([]() {}); // <-- one problem is here.
node->subscribe_inventory(
std::bind(&session::inventory, this_ptr, _1, node));
}
已经被破坏，并且在执行帖子期间访问权限将在某处失败。