99 lines
2.8 KiB
C++
99 lines
2.8 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2018 Danny Robson <danny@nerdcruft.net>
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*/
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#include "thread/flag.hpp"
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#include "thread/ticketlock.hpp"
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#include "tap.hpp"
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#include <mutex>
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#include <thread>
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///////////////////////////////////////////////////////////////////////////////
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using ffs_t = std::chrono::high_resolution_clock;
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//-----------------------------------------------------------------------------
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void
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fight (cruft::thread::flag &start, cruft::thread::ticketlock &l, int total, ffs_t::time_point &finish) {
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start.wait ();
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for (int count = 0; count < total; ++count)
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std::lock_guard g (l);
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finish = std::chrono::high_resolution_clock::now ();
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};
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//-----------------------------------------------------------------------------
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int
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main ()
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{
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cruft::TAP::logger tap;
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cruft::thread::ticketlock l;
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l.lock ();
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tap.expect (true, "locked without contention");
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l.unlock ();
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tap.expect (true, "unlocked without contention");
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if (true || std::thread::hardware_concurrency () < 2) {
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tap.skip ("reasonably fair under contention");
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} else {
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// measure fairness under contention is below some threshold
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//
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// * create two threads that will fight over a lock
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// * measure the start time
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// * fire an event to start the threads
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// * record the time the threads finish
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// * compare the difference in runtimes as a percentage
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//
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// we have to be reasonably generous with our test at the end because
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// there's liable to be a lot of noise in the measurement with a test
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// that runs in a short enough time period.
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constexpr int iterations = 1 << 16;
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cruft::thread::flag start_flag;
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ffs_t::time_point a_finish, b_finish;
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std::thread a (
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fight,
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std::ref (start_flag),
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std::ref (l),
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iterations,
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std::ref (a_finish)
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);
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std::thread b (
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fight,
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std::ref (start_flag),
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std::ref (l),
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iterations,
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std::ref (b_finish)
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);
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auto start = std::chrono::high_resolution_clock::now ();
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start_flag.notify_all ();
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a.join ();
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b.join ();
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auto a_total = std::chrono::duration_cast<std::chrono::nanoseconds> (a_finish - start).count ();
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auto b_total = std::chrono::duration_cast<std::chrono::nanoseconds> (b_finish - start).count ();
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auto diff = cruft::max (a_total, b_total) / float (cruft::min (a_total, b_total));
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auto rel = cruft::abs (1 - diff);
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tap.expect_lt (rel, 0.1f, "reasonably fair under contention");
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}
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return tap.status ();
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}
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