Question

当我在方法deadline_timer::async_wait中调用SendMessageAgain时，会偶尔抛出一个段错误。它可以通过两种方式之一发生;我在下面列出了回溯。它似乎是随机的，这让我觉得某种程度上涉及竞争条件。我有一个带有io_service对象ioService的类，以及多个线程，每个线程都有定时器挂钩到ioService。在调用ioService之前，我是否需要锁定async_wait？我认为它处理了这个问题。

当计时器滴答时，它可能与任何代码被中断有关。在其他代码执行时设置截止时间计时器的正确方法是什么？

我在SendMessageAgain中使用的代码是

void Node::SendMessageAgain(unsigned long seqNum) {
  // figure out if and what to send (using object fields)
  if (should_send_again) {
    Send(...);
    timer->expires_from_now(INTERVAL);
    timer->async_wait(bind(&Node::SendMessageAgain, this, seqNum));
  }
}

#0  0x08060609 in boost::asio::detail::deadline_timer_service<boost::asio::time_traits<boost::posix_time::ptime> >::async_wait<boost::_bi::bind_t<void, boost::_mfi::mf1<void, Node, unsigned long>, boost::_bi::list2<boost::_bi::value<Node*>, boost::_bi::value<unsigned long> > > > (this=0x14, impl=..., handler=...)
    at /usr/include/boost/asio/detail/deadline_timer_service.hpp:170
#1  0x0805e2e7 in boost::asio::deadline_timer_service<boost::posix_time::ptime, boost::asio::time_traits<boost::posix_time::ptime> >::async_wait<boost::_bi::bind_t<void, boost::_mfi::mf1<void, Node, unsigned long>, boost::_bi::list2<boost::_bi::value<Node*>, boost::_bi::value<unsigned long> > > > (this=0x0, impl=..., 
    handler=...) at /usr/include/boost/asio/deadline_timer_service.hpp:135
#2  0x0805bcbb in boost::asio::basic_deadline_timer<boost::posix_time::ptime, boost::asio::time_traits<boost::posix_time::ptime>, boost::asio::deadline_timer_service<boost::posix_time::ptime, boost::asio::time_traits<boost::posix_time::ptime> > >::async_wait<boost::_bi::bind_t<void, boost::_mfi::mf1<void, Node, unsigned long>, boost::_bi::list2<boost::_bi::value<Node*>, boost::_bi::value<unsigned long> > > > (this=0x807fc50, handler=...)
    at /usr/include/boost/asio/basic_deadline_timer.hpp:435
#3  0x080555a2 in Node::SendMessageAgain (this=0xbfffefdc, seqNum=8)
    at node.cpp:147

#0  __pthread_mutex_lock (mutex=0x2f200c4) at pthread_mutex_lock.c:50
#1  0x08056c79 in boost::asio::detail::posix_mutex::lock (this=0x2f200c4)
    at /usr/include/boost/asio/detail/posix_mutex.hpp:52
#2  0x0805a036 in boost::asio::detail::scoped_lock<boost::asio::detail::posix_mutex>::scoped_lock (this=0xbfffeb04, m=...)
    at /usr/include/boost/asio/detail/scoped_lock.hpp:36
#3  0x08061dd0 in boost::asio::detail::epoll_reactor::schedule_timer<boost::asio::time_traits<boost::posix_time::ptime> > (this=0x2f200ac, queue=..., 
    time=..., timer=..., op=0x807fca0)
    at /usr/include/boost/asio/detail/impl/epoll_reactor.hpp:43
#4  0x0806063a in boost::asio::detail::deadline_timer_service<boost::asio::time_traits<boost::posix_time::ptime> >::async_wait<boost::_bi::bind_t<void, boost::_mfi::mf1<void, Node, unsigned long>, boost::_bi::list2<boost::_bi::value<Node*>, boost::_bi::value<unsigned long> > > > (this=0xb6b005fc, impl=..., 
    handler=...)
    at /usr/include/boost/asio/detail/deadline_timer_service.hpp:170
#5  0x0805e2fd in boost::asio::deadline_timer_service<boost::posix_time::ptime, boost::asio::time_traits<boost::posix_time::ptime> >::async_wait<boost::_bi::bind_t<void, boost::_mfi::mf1<void, Node, unsigned long>, boost::_bi::list2<boost::_bi::value<Node*>, boost::_bi::value<unsigned long> > > > (this=0xb6b005e8, 
    impl=..., handler=...)
    at /usr/include/boost/asio/deadline_timer_service.hpp:135
#6  0x0805bcd1 in boost::asio::basic_deadline_timer<boost::posix_time::ptime, bo---Type <return> to continue, or q <return> to quit---
ost::asio::time_traits<boost::posix_time::ptime>, boost::asio::deadline_timer_service<boost::posix_time::ptime, boost::asio::time_traits<boost::posix_time::ptime> > >::async_wait<boost::_bi::bind_t<void, boost::_mfi::mf1<void, Node, unsigned long>, boost::_bi::list2<boost::_bi::value<Node*>, boost::_bi::value<unsigned long> > > > (this=0xb6b005a0, handler=...)
    at /usr/include/boost/asio/basic_deadline_timer.hpp:435
#7  0x080555a7 in Node::SendMessageAgain (this=0xbfffefdc, seqNum=9)
    at node.cpp:148

Answer 1

好的，它是固定的。正如Sam建议的那样，这是一个对象生命周期问题，但不是Node。我在Node拥有的对象中有一个计时器。在我的代码中有一个竞争条件，我在关键部分之外重置计时器，它的所有者在关键部分结束和重置计时器之间被销毁。我只是扩展了关键部分并修复了它。

我不确定为什么segfault在async_wait中表现得如此之差，因为回调（以及相关的this指针）属于Node，它仍然存在。< / p>

Answer 2

为：

timer->async_wait(bind(&Node::SendMessageAgain, this, seqNum, _1));

好：

timer->async_wait(bind(&Node::SendMessageAgain, shared_from_this(), seqNum, _1));

让节点扩展enable_shared_from_this

class Node : public boost::enable_shared_from_this<Node>

这可以解决问题，如果它是由你的Node被销毁而仍在为它调度回调而造成的。

在boost :: asio :: deadline_timer :: async_wait中的Segfault

2 个答案: