libcruft-util/test/thread/semaphore.cpp

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#include "thread/semaphore.hpp"
#include "thread/flag.hpp"
#include "tap.hpp"
#include <mutex>
#include <thread>
///////////////////////////////////////////////////////////////////////////////
void
fight (cruft::thread::semaphore &sem, const int iterations)
{
for (int i = 0; i < iterations; ++i) {
std::lock_guard tmp {sem};
(void)tmp;
}
}
///////////////////////////////////////////////////////////////////////////////
int
main ()
{
cruft::TAP::logger tap;
{
cruft::thread::semaphore sem (0);
tap.expect_eq (sem.value (), 0, "initialisation is respected");
tap.expect_eq (sem.unlock (), 1, "bare release increments without blocking");
tap.expect_eq (sem.lock (), 0, "bare acquire decrements without blocking");
}
// test that two threads can cooperate on a single semaphore.
{
cruft::thread::semaphore sem (1);
// the spawned thread attempts to double acquire a semaphore with
// only one available and so should get blocked immediately.
std::atomic<int> test = 0;
std::thread t ([&] () {
sem.lock ();
sem.lock ();
test = 1;
});
// wait until we know the thread should have been blocked. it should
// not have touched the 'test' variable at this point.
while (sem.value () > 0)
std::this_thread::yield ();
tap.expect_eq (test, 0, "locking blocks in foreign thread");
// unlock the semaphore, wait for the thread to finish, and check it
// touched the 'test' variable.
sem.unlock ();
t.join ();
tap.expect_eq (test, 1, "unlocking resumes foreign thread");
}
{
const auto parallelism = std::thread::hardware_concurrency ();
constexpr int iterations = 1 << 16;
std::vector<std::thread> threads;
cruft::thread::semaphore sem (0);
for (unsigned i = 0; i < parallelism; ++i)
threads.emplace_back (fight, std::ref (sem), iterations);
sem.unlock ();
sem.unlock ();
for (auto &t: threads)
t.join ();
tap.expect (true, "high concurrency didn't deadlock");
}
return tap.status ();
}