boost.asio的又一个bug.

最近在设计一个多线程分块支持续传的http的异步客户端时, 测试部门常常发现http下载模
块退出时偶尔会卡住, 在win7系统上由为明显. 反复检查代码, 并未明显问题, 因而专门写
了一个反复退出的单元测试, 当即发现问题, 并定位在io_service的析构函数中, 奇怪的是,
个人投递io的全部socket都早已经关闭, run线程也已经退出, 按理说, 这时的io_service的
outstanding_work_应该为0才是, 可我一看它倒是1, 因而始终在win_iocp_io_service.hpp的
shutdown_service里一直循环调用GetQueuedCompletionStatus, 从而致使没法正常退出...
很明显, 这是asio对outstanding_work_计数维护的有问题, 为了解决
问题, 因而我很快想到不使用iocp, 添加宏BOOST_ASIO_DISABLE_IOCP一切就正常了...
因为本身使用的是boost.1.45版本, 因而换了个boost.1.46.1再试试, 结果同样. 难道这么严
重的bug跨在了这两个很是重要的发行版本上而没人知道?
在官方的邮件列表中细节检查, 终于看到了某人的bug报告和我描述的状况差很少, 并且
在那我的报告了bug的次日, asio做者就发布了补丁, 但这个补丁并未更新到boost.1.45
和boost.1.46中, 唉, 这两个版本但是大版本啊, 估计受害人很多...
不过幸运的是, 我在boost的主分枝中看到了修正的代码.
下面是这个补丁内容:

From 81a6a51c0cb66de6bc77e1fa5dcd46b2794995e4 Mon Sep 17 00:00:00 2001
From: Christopher Kohlhoff <chris@kohlhoff.com>
Date: Wed, 23 Mar 2011 15:03:56 +1100
Subject: [PATCH] On Windows, ensure the count of outstanding work is decremented for
 abandoned operations (i.e. operations that are being cleaned up within
 the io_service destructor).

---
 asio/include/asio/detail/impl/dev_poll_reactor.ipp |    2 ++
 asio/include/asio/detail/impl/epoll_reactor.ipp    |    2 ++
 asio/include/asio/detail/impl/kqueue_reactor.ipp   |    2 ++
 asio/include/asio/detail/impl/select_reactor.ipp   |    2 ++
 .../asio/detail/impl/signal_set_service.ipp        |    2 ++
 asio/include/asio/detail/impl/task_io_service.ipp  |    7 +++++++
 .../asio/detail/impl/win_iocp_io_service.ipp       |   11 +++++++++++
 asio/include/asio/detail/task_io_service.hpp       |    4 ++++
 asio/include/asio/detail/win_iocp_io_service.hpp   |    4 ++++
 9 files changed, 36 insertions(+), 0 deletions(-)

diff --git a/asio/include/asio/detail/impl/dev_poll_reactor.ipp b/asio/include/asio/detail/impl/dev_poll_reactor.ipp
index 06d89ea..2a01993 100644
--- a/asio/include/asio/detail/impl/dev_poll_reactor.ipp
+++ b/asio/include/asio/detail/impl/dev_poll_reactor.ipp
@@ -63,6 +63,8 @@ void dev_poll_reactor::shutdown_service()
     op_queue_[i].get_all_operations(ops);
 
   timer_queues_.get_all_timers(ops);
+
+  io_service_.abandon_operations(ops);
 } 
 
 // Helper class to re-register all descriptors with /dev/poll.
diff --git a/asio/include/asio/detail/impl/epoll_reactor.ipp b/asio/include/asio/detail/impl/epoll_reactor.ipp
index 22f567a..d08dedb 100644
--- a/asio/include/asio/detail/impl/epoll_reactor.ipp
+++ b/asio/include/asio/detail/impl/epoll_reactor.ipp
@@ -84,6 +84,8 @@ void epoll_reactor::shutdown_service()
   }
 
   timer_queues_.get_all_timers(ops);
+
+  io_service_.abandon_operations(ops);
 }
 
 void epoll_reactor::fork_service(asio::io_service::fork_event fork_ev)
diff --git a/asio/include/asio/detail/impl/kqueue_reactor.ipp b/asio/include/asio/detail/impl/kqueue_reactor.ipp
index f0cdf73..45aff60 100644
--- a/asio/include/asio/detail/impl/kqueue_reactor.ipp
+++ b/asio/include/asio/detail/impl/kqueue_reactor.ipp
@@ -74,6 +74,8 @@ void kqueue_reactor::shutdown_service()
   }
 
   timer_queues_.get_all_timers(ops);
+
+  io_service_.abandon_operations(ops);
 }
 
 void kqueue_reactor::fork_service(asio::io_service::fork_event fork_ev)
diff --git a/asio/include/asio/detail/impl/select_reactor.ipp b/asio/include/asio/detail/impl/select_reactor.ipp
index f4e0314..00fd9fc 100644
--- a/asio/include/asio/detail/impl/select_reactor.ipp
+++ b/asio/include/asio/detail/impl/select_reactor.ipp
@@ -81,6 +81,8 @@ void select_reactor::shutdown_service()
     op_queue_[i].get_all_operations(ops);
 
   timer_queues_.get_all_timers(ops);
+
+  io_service_.abandon_operations(ops);
 }
 
 void select_reactor::fork_service(asio::io_service::fork_event fork_ev)
diff --git a/asio/include/asio/detail/impl/signal_set_service.ipp b/asio/include/asio/detail/impl/signal_set_service.ipp
index f0f0e78..4cde184 100644
--- a/asio/include/asio/detail/impl/signal_set_service.ipp
+++ b/asio/include/asio/detail/impl/signal_set_service.ipp
@@ -145,6 +145,8 @@ void signal_set_service::shutdown_service()
       reg = reg->next_in_table_;
     }
   }
+
+  io_service_.abandon_operations(ops);
 }
 
 void signal_set_service::fork_service(
diff --git a/asio/include/asio/detail/impl/task_io_service.ipp b/asio/include/asio/detail/impl/task_io_service.ipp
index cb585d5..0a2c6fa 100644
--- a/asio/include/asio/detail/impl/task_io_service.ipp
+++ b/asio/include/asio/detail/impl/task_io_service.ipp
@@ -230,6 +230,13 @@ void task_io_service::post_deferred_completions(
   }
 }
 
+void task_io_service::abandon_operations(
+    op_queue<task_io_service::operation>& ops)
+{
+  op_queue<task_io_service::operation> ops2;
+  ops2.push(ops);
+}
+
 std::size_t task_io_service::do_one(mutex::scoped_lock& lock,
     task_io_service::idle_thread_info* this_idle_thread)
 {
diff --git a/asio/include/asio/detail/impl/win_iocp_io_service.ipp b/asio/include/asio/detail/impl/win_iocp_io_service.ipp
index ca3125e..7aaa6b8 100644
--- a/asio/include/asio/detail/impl/win_iocp_io_service.ipp
+++ b/asio/include/asio/detail/impl/win_iocp_io_service.ipp
@@ -262,6 +262,17 @@ void win_iocp_io_service::post_deferred_completions(
   }
 }
 
+void win_iocp_io_service::abandon_operations(
+    op_queue<win_iocp_operation>& ops)
+{
+  while (win_iocp_operation* op = ops.front())
+  {
+    ops.pop();
+    ::InterlockedDecrement(&outstanding_work_);
+    op->destroy();
+  }
+}
+
 void win_iocp_io_service::on_pending(win_iocp_operation* op)
 {
   if (::InterlockedCompareExchange(&op->ready_, 1, 0) == 1)
diff --git a/asio/include/asio/detail/task_io_service.hpp b/asio/include/asio/detail/task_io_service.hpp
index 285d83e..654f83c 100644
--- a/asio/include/asio/detail/task_io_service.hpp
+++ b/asio/include/asio/detail/task_io_service.hpp
@@ -105,6 +105,10 @@ public:
   // that work_started() was previously called for each operation.
   ASIO_DECL void post_deferred_completions(op_queue<operation>& ops);
 
+  // Process unfinished operations as part of a shutdown_service operation.
+  // Assumes that work_started() was previously called for the operations.
+  ASIO_DECL void abandon_operations(op_queue<operation>& ops);
+
 private:
   // Structure containing information about an idle thread.
   struct idle_thread_info;
diff --git a/asio/include/asio/detail/win_iocp_io_service.hpp b/asio/include/asio/detail/win_iocp_io_service.hpp
index a562834..b5d7f0b 100644
--- a/asio/include/asio/detail/win_iocp_io_service.hpp
+++ b/asio/include/asio/detail/win_iocp_io_service.hpp
@@ -126,6 +126,10 @@ public:
   ASIO_DECL void post_deferred_completions(
       op_queue<win_iocp_operation>& ops);
 
+  // Enqueue unfinished operation as part of a shutdown_service operation.
+  // Assumes that work_started() was previously called for the operations.
+  ASIO_DECL void abandon_operations(op_queue<operation>& ops);
+
   // Called after starting an overlapped I/O operation that did not complete
   // immediately. The caller must have already called work_started() prior to
   // starting the operation.
-- 
1.7.0.1

注: 在boost.asio中, 使用这个补丁时, 须要将ASIO_DECL 改为 BOOST_ ASIO_DECL
注: 最新发布的boost1.47版本已经修复了这个bug, 建议尽可能采用新版本的boost.

这是我第二次在使用asio的过程当中, 发现的比较严重的bug了, 不过幸运的是, 每一次都能在官方的论坛 
或邮件列表中找到解决方案. 

结论, 再牛的人写的代码也会有bug, 我的很是崇拜asio的做者.