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Code Issues Releases Wiki Activity

ircd::net::dns::resolver: Improve timeout cycle; avoid false positives under load.

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This commit is contained in:
Jason Volk 2020-11-06 21:33:30 -08:00
parent 27d0c25f9b
commit 04f6e9692a
2 changed files with 52 additions and 15 deletions
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2
include/ircd/net/dns_resolver.h
View file

@ -46,6 +46,7 @@ struct ircd::net::dns::resolver
steady_point send_last; // Time of last send
std::deque<uint16_t> sendq; // Queue of frames for rate-limiting
ip::udp::socket ns; // A pollable activity object
bool recv_idle {false}; // Timeout worker won't run if false
// util
void add_server(const ipport &);
@ -67,6 +68,7 @@ struct ircd::net::dns::resolver
void handle_reply(const header &, const const_buffer &body, tag &);
void handle_reply(const ipport &, const header &, const const_buffer &body);
void handle(const ipport &, const mutable_buffer &);
void handle_interrupt(ctx::ctx *const &) noexcept;
std::tuple<net::ipport, mutable_buffer> recv_recv(const mutable_buffer &);
void recv_worker();
ctx::context recv_context;

65
ircd/net_dns_resolver.cc
View file

@ -286,9 +286,12 @@ ircd::net::dns::resolver::timeout_worker()
{
while(1)
{
// Dock here until somebody submits a request into the tag map. Also
// wait until recv_idle is asserted which indicates the UDP queue has
// been exhausted.
dock.wait([this]
{
return !tags.empty();
return !tags.empty() && recv_idle;
});
check_timeouts(milliseconds(timeout));
@ -526,37 +529,69 @@ catch(const std::exception &e)
std::tuple<ircd::net::ipport, ircd::mutable_buffer>
ircd::net::dns::resolver::recv_recv(const mutable_buffer &buf)
{
static const ip::udp::socket::message_flags flags
{
0
};
const asio::mutable_buffers_1 bufs
{
buf
};
const auto interruption{[this](ctx::ctx *const &)
{
if(this->ns.is_open())
this->ns.cancel();
}};
// First try a non-blocking receive to find and return anything in the
// queue. If this comes back as -EAGAIN we'll assert recv_idle and then
// conduct the normal blocking receive.
boost::system::error_code ec;
ip::udp::endpoint ep;
size_t recv; continuation
size_t recv
{
continuation::asio_predicate, interruption, [this, &bufs, &recv, &ep]
(auto &yield)
{
recv = ns.async_receive_from(bufs, ep, yield);
}
ns.receive_from(bufs, ep, flags, ec)
};
assert(!ec || recv == 0);
assert(!ec || ec == boost::system::errc::resource_unavailable_try_again);
// branch on any ec, not just -EAGAIN; this time it can throw...
if(likely(ec))
{
const scope_restore recv_idle
{
this->recv_idle, true
};
const auto interruption
{
std::bind(&resolver::handle_interrupt, this, ph::_1)
};
continuation
{
continuation::asio_predicate, interruption, [this, &bufs, &recv, &ep]
(auto &yield)
{
recv = ns.async_receive_from(bufs, ep, yield);
}
};
}
return
{
make_ipport(ep),
mutable_buffer
make_ipport(ep), mutable_buffer
{
data(buf), recv
}
};
}
void
ircd::net::dns::resolver::handle_interrupt(ctx::ctx *const &interruptor)
noexcept
{
if(!ns.is_open())
ns.cancel();
}
void
ircd::net::dns::resolver::handle(const ipport &from,
const mutable_buffer &buf)