http_client hangs when upload many files at the same time

[LiShuangcheng84]

the code:
pplx::task RestAdapter::UploadTask(const std::string& url, const std::string& fid,
const std::string& filePath, RestCallback callback, void* context)
{
return file_stream<uint8_t>::open_istream(filePath).then([=](istream stream) {
http_client_config config;
config.set_timeout(utility::seconds(1));
http_client client("http://" + url);
return client.request(methods::PUT, uri_builder().append_path(fid).to_string(), stream)
.then([=] (http_response response) {
// stream.close();
if (response.status_code() != status_codes::Created) {
LOG_ERROR("Upload:%s to http://%s/%s failed:%u.", filePath.c_str(), url.c_str(), fid.c_str(), response.status_code());
callback(false, context);
} else {
LOG_DEBUG("Upload:%s to http://%s/%s successfully:%u.", filePath.c_str(), url.c_str(), fid.c_str(), response.status_code());
callback(true, context);
}
});
});
}

all asio threads have same bt like this:
(gdb) bt
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x00007fee17e994dc in std::condition_variable::wait(std::unique_lockstd::mutex&) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#2 0x00007fee183b0bc5 in std::condition_variable::wait<pplx::details::event_impl::wait(unsigned int)::{lambda()#1}>(std::unique_lockstd::mutex&, pplx::detai ls::event_impl::wait(unsigned int)::{lambda()#1}) (this=0x7fee0803fb20, __lock=..., __p=...) at /usr/include/c++/4.8/condition_variable:93
#3 0x00007fee183ab942 in pplx::details::event_impl::wait (this=0x7fee0803faf8, timeout=4294967295)
at /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/include/pplx/pplxlinux.h:98
#4 0x00007fee183aba09 in pplx::details::event_impl::wait (this=0x7fee0803faf8)
at /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/include/pplx/pplxlinux.h:113
#5 0x00007fee183acfa8 in pplx::details::_TaskCollectionImpl::_Wait (this=0x7fee0803faf8)
at /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/include/pplx/pplx.h:161
#6 0x00007fee183acf8e in pplx::details::_TaskCollectionImpl::_RunAndWait (this=0x7fee0803faf8)
at /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/include/pplx/pplx.h:158
#7 0x00007fee183adaf7 in pplx::details::_Task_impl_base::_Wait (this=0x7fee0803fa98)
at /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/include/pplx/pplxtasks.h:1777
#8 0x00007fee183b20c2 in pplx::task::wait (this=0x7fedfbffe380)
at /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/include/pplx/pplxtasks.h:3601
#9 0x00007fee183aeeb2 in pplx::task::wait (this=0x7fedfbffe380)
at /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/include/pplx/pplxtasks.h:4594
#10 0x00007fee183e720b in Concurrency::streams::details::basic_file_buffer::basic_file_buffer (this=0x7fedb0001520, __in_chrg=)
at /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/include/cpprest/filestream.h:99
#11 0x00007fee183e729e in Concurrency::streams::details::basic_file_buffer::basic_file_buffer (this=0x7fedb0001520, __in_chrg=)
at /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/include/cpprest/filestream.h:106
#12 0x00007fee183f497a in std::_Sp_counted_ptr<Concurrency::streams::details::basic_file_buffer*, (__gnu_cxx::_Lock_policy)2>::_M_dispose (
this=0x7fedb0001640) at /usr/include/c++/4.8/bits/shared_ptr_base.h:290
#13 0x0000000000456784 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7fedb0001640)
at /usr/include/c++/4.8/bits/shared_ptr_base.h:144
#14 0x0000000000455ffd in std::__shared_count<(__gnu_cxx::_Lock_policy)2>::__shared_count (this=0x7fedb8001598, __in_chrg=)
at /usr/include/c++/4.8/bits/shared_ptr_base.h:546
#15 0x00007fee183b09d4 in std::__shared_ptr<Concurrency::streams::details::basic_streambuf, (__gnu_cxx::_Lock_policy)2>::__shared_ptr (
this=0x7fedb8001590, __in_chrg=) at /usr/include/c++/4.8/bits/shared_ptr_base.h:781
#16 0x00007fee183b0a14 in std::shared_ptr<Concurrency::streams::details::basic_streambuf >::~shared_ptr (this=0x7fedb8001590,
__in_chrg=) at /usr/include/c++/4.8/bits/shared_ptr.h:93
#17 0x00007fee183b39c4 in Concurrency::streams::streambuf::~streambuf (this=0x7fedb8001588, __in_chrg=)
at /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/include/cpprest/astreambuf.h:876
#18 0x00007fee183e4de6 in Concurrency::streams::details::basic_istream_helper::~basic_istream_helper (this=0x7fedb8001588,
__in_chrg=) at /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/include/cpprest/streams.h:53
#19 0x00007fee183df524 in __gnu_cxx::new_allocator<Concurrency::streams::details::basic_istream_helper >::destroy<Concurrency::streams::details: :basic_istream_helper > (this=0x7fedb8001580, __p=0x7fedb8001588) at /usr/include/c++/4.8/ext/new_allocator.h:124
#20 0x00007fee183daded in std::allocator_traits<std::allocator<Concurrency::streams::details::basic_istream_helper > >::_S_destroy<Concurrency:: streams::details::basic_istream_helper > (__a=..., __p=0x7fedb8001588) at /usr/include/c++/4.8/bits/alloc_traits.h:281
#21 0x00007fee183d71a7 in std::allocator_traits<std::allocator<Concurrency::streams::details::basic_istream_helper > >::destroy<Concurrency::str eams::details::basic_istream_helper > (__a=..., __p=0x7fedb8001588) at /usr/include/c++/4.8/bits/alloc_traits.h:405
#22 0x00007fee183d08f5 in std::_Sp_counted_ptr_inplace<Concurrency::streams::details::basic_istream_helper, std::allocator<Concurrency::streams: :details::basic_istream_helper >, (__gnu_cxx::_Lock_policy)2>::_M_dispose (this=0x7fedb8001570)
at /usr/include/c++/4.8/bits/shared_ptr_base.h:407
#23 0x0000000000456784 in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7fedb8001570)
at /usr/include/c++/4.8/bits/shared_ptr_base.h:144
---Type to continue, or q to quit---
#24 0x00007fee167f5c01 in web::http::details::http_msg_base::set_body(Concurrency::streams::basic_istream const&, std::string const&) ()
from /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/libs/libcpprest.so.2.10
#25 0x00007fee167e12ca in web::http::client::details::request_context::complete_headers() ()
from /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/libs/libcpprest.so.2.10
#26 0x00007fee16906144 in web::http::client::details::asio_context::read_headers() ()
from /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/libs/libcpprest.so.2.10
#27 0x00007fee1690b747 in web::http::client::details::asio_context::handle_status_line(boost::system::error_code const&) ()
from /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/libs/libcpprest.so.2.10
#28 0x00007fee168eec93 in boost::asio::detail::read_until_delim_string_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_ser viceboost::asio::ip::tcp >, std::allocator, boost::_bi::bind_t<void, boost::_mfi::mf1<void, web::http::client::details::asio_context, boost::system::er ror_code const&>, boost::_bi::list2<boost::_bi::value<std::shared_ptrweb::http::client::details::asio_context >, boost::arg<1> ()()> > >::operator()(boost:: system::error_code const&, unsigned long, int) () from /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/libs/libcpprest.so.2.10
#29 0x00007fee168ef2db in boost::asio::detail::reactive_socket_recv_op<boost::asio::mutable_buffers_1, boost::asio::detail::read_until_delim_string_op<boost::a sio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_serviceboost::asio::ip::tcp >, std::allocator, boost::_bi::bind_t<void, boost ::_mfi::mf1<void, web::http::client::details::asio_context, boost::system::error_code const&>, boost::_bi::list2<boost::_bi::value<std::shared_ptr<web::http::c lient::details::asio_context> >, boost::arg<1> ()()> > > >::do_complete(boost::asio::detail::task_io_service*, boost::asio::detail::task_io_service_operation* , boost::system::error_code const&, unsigned long) () from /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/libs/libcpprest.so.2.10
#30 0x00007fee1685f69f in boost::asio::detail::task_io_service::run(boost::system::error_code&) ()
from /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/libs/libcpprest.so.2.10
#31 0x00007fee168e0c17 in boost::asio::detail::posix_thread::func<(anonymous namespace)::threadpool_impl::add_thread()::{lambda()#1}>::run() ()
from /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/libs/libcpprest.so.2.10
#32 0x00007fee1685022f in boost_asio_detail_posix_thread_function ()
from /workspace/code/Venom/code/storage.client/../../third_party/cpprestsdk/libs/libcpprest.so.2.10
#33 0x00007fee186b9184 in start_thread (arg=0x7fedfbfff700) at pthread_create.c:312
#34 0x00007fee1790a03d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

[LiShuangcheng84]

[zzzhr1990]

Seems the max concurrent task limit is 64 (the default thread pool size?)
(Just on OSX/Linux, On windows, everything is ok)

int main() {
    const int MAX_THREAD_ID = 62; // if change this above 63, program will be blocked forever.
    std::vector<pplx::task<int>> u;
    web::http::client::http_client client(_XPLATSTR("https://www.microsoft.com"));
    for(int i =0;i<= MAX_THREAD_ID;i++)
    {
        auto t = pplx::create_task([&client]{
            web::http::http_request req;
            req.set_method(web::http::methods::GET);
            try {
                return static_cast<int>(client.request(req).get().status_code());
            }catch (const std::exception& exx) {
                std::cout << exx.what() << std::endl;
            }
            return -1;
        });
        u.emplace_back(t);
    }

    auto complete = pplx::when_all(u.begin(), u.end()).get();
    for(auto re: complete){
        std::cout << "result: " << re << std::endl;
    }

    std::cout << "-fin-" << std::endl; // 200

    std::cin.get();
    return 0;
}