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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: no-threads
// UNSUPPORTED: c++03, c++11
// <shared_mutex>
// class shared_timed_mutex;
// void lock_shared();
#include <shared_mutex>
#include <algorithm>
#include <atomic>
#include <cassert>
#include <thread>
#include <vector>
#include "make_test_thread.h"
int main(int, char**) {
// Lock-shared a mutex that is not locked yet. This should succeed.
{
std::shared_timed_mutex m;
std::vector<std::thread> threads;
for (int i = 0; i != 5; ++i) {
threads.push_back(support::make_test_thread([&] {
m.lock_shared();
m.unlock_shared();
}));
}
for (auto& t : threads)
t.join();
}
// Lock-shared a mutex that is already exclusively locked. This should block until it is unlocked.
{
std::atomic<int> ready(0);
std::shared_timed_mutex m;
m.lock();
std::atomic<bool> is_locked_from_main(true);
std::vector<std::thread> threads;
for (int i = 0; i != 5; ++i) {
threads.push_back(support::make_test_thread([&] {
++ready;
while (ready < 5)
/* wait until all threads have been created */;
m.lock_shared();
assert(!is_locked_from_main);
m.unlock_shared();
}));
}
while (ready < 5)
/* wait until all threads have been created */;
// We would rather signal this after we unlock, but that would create a race condition.
// We instead signal it before we unlock, which means that it's technically possible for
// the thread to take the lock while we're still holding it and for the test to still pass.
is_locked_from_main = false;
m.unlock();
for (auto& t : threads)
t.join();
}
// Lock-shared a mutex that is already lock-shared. This should succeed.
{
std::atomic<int> ready(0);
std::shared_timed_mutex m;
m.lock_shared();
std::vector<std::thread> threads;
for (int i = 0; i != 5; ++i) {
threads.push_back(support::make_test_thread([&] {
++ready;
while (ready < 5)
/* wait until all threads have been created */;
m.lock_shared();
m.unlock_shared();
}));
}
while (ready < 5)
/* wait until all threads have been created */;
m.unlock_shared();
for (auto& t : threads)
t.join();
}
// Create several threads that all acquire-shared the same mutex and make sure that each
// thread successfully acquires-shared the mutex.
//
// We record how many other threads were holding the mutex when it was acquired, which allows
// us to know whether the test was somewhat effective at causing multiple threads to lock at
// the same time.
{
std::shared_timed_mutex mutex;
std::vector<std::thread> threads;
constexpr int n_threads = 5;
std::atomic<int> holders(0);
int concurrent_holders[n_threads] = {};
std::atomic<bool> ready(false);
for (int i = 0; i != n_threads; ++i) {
threads.push_back(support::make_test_thread([&, i] {
while (!ready)
/* spin */;
mutex.lock_shared();
++holders;
concurrent_holders[i] = holders;
mutex.unlock_shared();
--holders;
}));
}
ready = true; // let the threads actually start shared-acquiring the mutex
for (auto& t : threads)
t.join();
// We can't guarantee that we'll ever have more than 1 concurrent holder so that's what
// we assert, however in principle we should often trigger more than 1 concurrent holder.
int max_concurrent_holders = *std::max_element(std::begin(concurrent_holders), std::end(concurrent_holders));
assert(max_concurrent_holders >= 1);
}
return 0;
}
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