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POboost::asio -- asio_handler_deallocate is called in io_service::~io_service(), after io_service::stop()
 

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  1. POboost::asio -- asio_handler_deallocate is called in io_service::~io_service(), after io_service::stop()
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    <p>I have an <code>ip::udp::socket</code> constructed with an <code>io_service</code>. There is only one <code>boost::thread</code> which calls the <code>io_service::run()</code> method, and an instance of <code>io_service::work</code> to prevent <code>io_service::run()</code> from returning. The completion handlers for my <code>ip::udp::socket</code> have custom <code>asio_handler_allocate()</code> and <code>asio_handler_deallocate()</code> functions, which are backed by a <code>my::custom_memory_pool</code>.</p> <p>When my application quits, this sequence of events occurs on on my shutting-down thread:</p> <ol> <li><code>ip::udp::socket::close()</code></li> <li><code>work::~work()</code></li> <li><code>io_service::stop()</code></li> <li><code>thread::join()</code></li> <li><code>my::custom_memory_pool::~custom_memory_pool()</code></li> <li><code>ip::udp::socket::~socket()</code></li> <li><code>thread::~thread()</code></li> <li><code>io_service::~io_service()</code></li> </ol> <p>In step 8, the call to <code>io_service::~io_service()</code> causes...</p> <pre><code>Program terminated with signal 11, Segmentation fault. #0 0x00000000005ad93c in my::custom_memory_pool&lt;boost::aligned_storage&lt;512u, -1u&gt; &gt;::deallocate (this=0x36323f8, t=0x7fca97a07880) at memory.hpp:82 82 reinterpret_cast&lt;pool_node*&gt;(t)-&gt;next_ = head_; (gdb) bt 30 #0 0x00000000005ad93c in my::custom_memory_pool&lt;boost::aligned_storage&lt;512u, -1u&gt; &gt;::deallocate (this=0x36323f8, t=0x7fca97a07880) at memory.hpp:82 #1 0x00000000005ad40a in asio_handler_deallocate (p=0x7fca97a07880, s=96, h=0x7fffe09d5480) at net.cpp:22 #2 0x0000000000571a07 in boost_asio_handler_alloc_helpers::deallocate&lt;socket_multicast::completion_handler&gt; (p=0x7fca97a07880, s=96, h=...) at /usr/include/boost/asio/detail/handler_alloc_helpers.hpp:51 #3 0x0000000000558256 in boost::asio::detail::reactive_socket_recvfrom_op&lt;boost::asio::mutable_buffers_1, boost::asio::ip::basic_endpoint&lt;boost::asio::ip::udp&gt;, socket_multicast::completion_handler&gt;::ptr::reset (this=0x7fffe09d54b0) at /usr/include/boost/asio/detail/reactive_socket_recvfrom_op.hpp:81 #4 0x0000000000558310 in boost::asio::detail::reactive_socket_recvfrom_op&lt;boost::asio::mutable_buffers_1, boost::asio::ip::basic_endpoint&lt;boost::asio::ip::udp&gt;, socket_multicast::completion_handler&gt;::do_complete (owner=0x0, base=0x7fca97a07880) at /usr/include/boost/asio/detail/reactive_socket_recvfrom_op.hpp:112 #5 0x0000000000426706 in boost::asio::detail::task_io_service_operation::destroy (this=0x7fca97a07880) at /usr/include/boost/asio/detail/task_io_service_operation.hpp:41 #6 0x000000000042841b in boost::asio::detail::task_io_service::shutdown_service (this=0xd4df30) at /usr/include/boost/asio/detail/impl/task_io_service.ipp:96 #7 0x0000000000426388 in boost::asio::detail::service_registry::~service_registry (this=0xd4a320, __in_chrg=&lt;value optimized out&gt;) at /usr/include/boost/asio/detail/impl/service_registry.ipp:43 #8 0x0000000000428e99 in boost::asio::io_service::~io_service (this=0xd49f38, __in_chrg=&lt;value optimized out&gt;) at /usr/include/boost/asio/impl/io_service.ipp:51 </code></pre> <p>So the <code>io_service::~io_service()</code> is trying to deallocate some memory to the pool that I destroyed back in step 5.</p> <p>I can't move <code>my::custom_memory_pool::~custom_memory_pool()</code> to after <code>io_service::~io_service()</code>.</p> <p>I expected that after <code>io_service::stop()</code> and <code>thread::join()</code> returns, there could be no more <code>asio_handler_deallocate()</code> calls. Apparently that's not the case. What can I do in step 3 to force <code>io_service</code> to dequeue all of its completion events and deallocate all of its handler memory, and how can I block until <code>io_service</code> finishes those tasks?</p>
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    1. USJames Brock
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    1. COMaybe I should move `work::~work()` to come after `io_service::stop()`... perhaps I'm not giving the `io_service` the opportunity to complete all operations.
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      1. USJames Brock
    2. COIf you're explicitly calling stop, then when you destory the `work` is irrelevant. The work only prevents the io_service from automatically stoping when it has no further tasks pending.
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      1. POboost::asio -- asio_handler_deallocate is called in io_service::~io_service(), after io_service::stop()
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    3. COThe asio docs: `io_service::stop()` means "Subsequent calls to run(), run_one(), poll() or poll_one() will return immediately." `work::~work()` means the end of the requirement that "the io_service object's run() function will not exit while work is underway." So the more I think about it, the more it seems that the proper order must be `io_service::stop()` then `work::~work()`, but the docs aren't explicit about that.
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      1. USJames Brock
 

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