From fd522ea75608c15542f643816f4a389d6cd63cea Mon Sep 17 00:00:00 2001
From: Alexander Shabalin <alexander.shabalin@jetbrains.com>
Date: Tue, 18 Jul 2023 17:05:59 +0200
Subject: [PATCH] [K/N] Add condition_variable that spins on atomics

---
 .../src/main/cpp/ConditionVariable.hpp        |  63 ++++
 .../src/main/cpp/ConditionVariableTest.cpp    | 353 ++++++++++++++++++
 2 files changed, 416 insertions(+)
 create mode 100644 kotlin-native/runtime/src/main/cpp/ConditionVariable.hpp
 create mode 100644 kotlin-native/runtime/src/main/cpp/ConditionVariableTest.cpp

diff --git a/kotlin-native/runtime/src/main/cpp/ConditionVariable.hpp b/kotlin-native/runtime/src/main/cpp/ConditionVariable.hpp
new file mode 100644
index 00000000000..5eb7c29a604
--- /dev/null
+++ b/kotlin-native/runtime/src/main/cpp/ConditionVariable.hpp
@@ -0,0 +1,63 @@
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the LICENSE file.
+ */
+
+#pragma once
+
+#include <atomic>
+#include <cinttypes>
+#include <thread>
+
+#include "Utils.hpp"
+
+namespace kotlin {
+
+// `std::condition_variable_any` implemented via spinning on atomics.
+class ConditionVariableSpin : private Pinned {
+public:
+    // Notify all threads waiting for `this.
+    // Exactly the same as `notify_all`. Providing this method to be fully compatible
+    // with `std::condition_variable_any`.
+    void notify_one() noexcept {
+        // Conditional variable does not protect the data: a mutex must be
+        // used to protect it, so we don't need synchronization.
+        epoch_.fetch_add(1, std::memory_order_relaxed);
+    }
+
+    // Notify all threads waiting for `this.
+    void notify_all() noexcept {
+        // Conditional variable does not protect the data: a mutex must be
+        // used to protect it, so we don't need synchronization.
+        epoch_.fetch_add(1, std::memory_order_relaxed);
+    }
+
+    // Wait until next call to `notify_*`.
+    template <typename Lock>
+    void wait(Lock& lock) {
+        auto currentEpoch = epoch_.load(std::memory_order_relaxed);
+        lock.unlock();
+        // Waiting for any change of the epoch.
+        while (epoch_.load(std::memory_order_relaxed) == currentEpoch) {
+            std::this_thread::yield();
+        }
+        lock.lock();
+    }
+
+    // Waits until `stopWaiting()` starts returning true. Any change
+    // that leads to `stopWaiting()` must be followed by `notify_*` for
+    // this `wait` to stop waiting.
+    template <typename Lock, typename Predicate>
+    void wait(Lock& lock, Predicate stopWaiting) {
+        while (!stopWaiting()) {
+            wait(lock);
+        }
+    }
+
+    // TODO: Implement wait_until and wait_for using kotlin::steady_clock.
+
+private:
+    std::atomic<size_t> epoch_ = 0;
+};
+
+} // namespace kotlin
diff --git a/kotlin-native/runtime/src/main/cpp/ConditionVariableTest.cpp b/kotlin-native/runtime/src/main/cpp/ConditionVariableTest.cpp
new file mode 100644
index 00000000000..a94e93176fa
--- /dev/null
+++ b/kotlin-native/runtime/src/main/cpp/ConditionVariableTest.cpp
@@ -0,0 +1,353 @@
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the LICENSE file.
+ */
+
+#include "ConditionVariable.hpp"
+
+#include <condition_variable>
+#include <mutex>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+#include "ScopedThread.hpp"
+#include "TestSupport.hpp"
+#include "std_support/Vector.hpp"
+
+using namespace kotlin;
+
+template <typename T>
+class ConditionVariableTest : public testing::Test {};
+
+using CVTypes = testing::Types<
+#ifndef KONAN_WINDOWS // winpthreads are acting strange in our mingw toolchain.
+        std::condition_variable,
+        std::condition_variable_any,
+#endif
+        ConditionVariableSpin>;
+class CVNames {
+public:
+    template <typename T>
+    static std::string GetName(int) {
+        if constexpr (std::is_same_v<T, std::condition_variable>) {
+            return "condition_variable";
+        } else if constexpr (std::is_same_v<T, std::condition_variable_any>) {
+            return "condition_variable_any";
+        } else if constexpr (std::is_same_v<T, ConditionVariableSpin>) {
+            return "ConditionVariableSpin";
+        }
+    }
+};
+TYPED_TEST_SUITE(ConditionVariableTest, CVTypes, CVNames);
+
+TYPED_TEST(ConditionVariableTest, NotifyNobody) {
+    using CVUnderTest = TypeParam;
+
+    CVUnderTest cv;
+    cv.notify_one();
+    cv.notify_all();
+}
+
+TYPED_TEST(ConditionVariableTest, WaitOne) {
+    using CVUnderTest = TypeParam;
+
+    bool flag = false;
+    std::mutex m;
+    CVUnderTest cv;
+
+    std::atomic<bool> waiting = false;
+    ScopedThread thread([&] {
+        std::unique_lock guard(m);
+        EXPECT_FALSE(flag);
+        waiting.store(true, std::memory_order_relaxed);
+        while (!flag) {
+            cv.wait(guard);
+        }
+    });
+
+    while (!waiting.load(std::memory_order_relaxed)) {
+        std::this_thread::yield();
+    }
+    {
+        std::unique_lock guard(m);
+        flag = true;
+    }
+    cv.notify_one();
+
+    thread.join();
+}
+
+TYPED_TEST(ConditionVariableTest, WaitOneNotifyUnderLock) {
+    using CVUnderTest = TypeParam;
+
+    bool flag = false;
+    std::mutex m;
+    CVUnderTest cv;
+
+    std::atomic<bool> waiting = false;
+    ScopedThread thread([&] {
+        std::unique_lock guard(m);
+        EXPECT_FALSE(flag);
+        waiting.store(true, std::memory_order_relaxed);
+        while (!flag) {
+            cv.wait(guard);
+        }
+    });
+
+    while (!waiting.load(std::memory_order_relaxed)) {
+        std::this_thread::yield();
+    }
+    {
+        std::unique_lock guard(m);
+        flag = true;
+        cv.notify_one();
+    }
+
+    thread.join();
+}
+
+TYPED_TEST(ConditionVariableTest, WaitAll) {
+    using CVUnderTest = TypeParam;
+
+    bool flag = false;
+    std::mutex m;
+    CVUnderTest cv;
+
+    std::atomic<size_t> waiting = 0;
+    std_support::vector<ScopedThread> threads;
+    for (int i = 0; i < kDefaultThreadCount; ++i) {
+        threads.emplace_back([&] {
+            std::unique_lock guard(m);
+            EXPECT_FALSE(flag);
+            waiting.fetch_add(1, std::memory_order_relaxed);
+            while (!flag) {
+                cv.wait(guard);
+            }
+        });
+    }
+
+    while (waiting.load(std::memory_order_relaxed) != threads.size()) {
+        std::this_thread::yield();
+    }
+    {
+        std::unique_lock guard(m);
+        flag = true;
+    }
+    cv.notify_all();
+
+    threads.clear();
+}
+
+TYPED_TEST(ConditionVariableTest, WaitAllNotifyUnderLock) {
+    using CVUnderTest = TypeParam;
+
+    bool flag = false;
+    std::mutex m;
+    CVUnderTest cv;
+
+    std::atomic<size_t> waiting = 0;
+    std_support::vector<ScopedThread> threads;
+    for (int i = 0; i < kDefaultThreadCount; ++i) {
+        threads.emplace_back([&] {
+            std::unique_lock guard(m);
+            EXPECT_FALSE(flag);
+            waiting.fetch_add(1, std::memory_order_relaxed);
+            while (!flag) {
+                cv.wait(guard);
+            }
+        });
+    }
+
+    while (waiting.load(std::memory_order_relaxed) != threads.size()) {
+        std::this_thread::yield();
+    }
+    {
+        std::unique_lock guard(m);
+        flag = true;
+        cv.notify_all();
+    }
+
+    threads.clear();
+}
+
+TYPED_TEST(ConditionVariableTest, WaitPredicateOne) {
+    using CVUnderTest = TypeParam;
+
+    bool flag = false;
+    std::mutex m;
+    CVUnderTest cv;
+
+    std::atomic<bool> waiting = false;
+    ScopedThread thread([&] {
+        std::unique_lock guard(m);
+        EXPECT_FALSE(flag);
+        waiting.store(true, std::memory_order_relaxed);
+        cv.wait(guard, [&] { return flag; });
+        EXPECT_TRUE(flag);
+    });
+
+    while (!waiting.load(std::memory_order_relaxed)) {
+        std::this_thread::yield();
+    }
+    {
+        std::unique_lock guard(m);
+        flag = true;
+    }
+    cv.notify_all();
+
+    thread.join();
+}
+
+TYPED_TEST(ConditionVariableTest, WaitPredicateOneNotifyUnderLock) {
+    using CVUnderTest = TypeParam;
+
+    bool flag = false;
+    std::mutex m;
+    CVUnderTest cv;
+
+    std::atomic<bool> waiting = 0;
+    ScopedThread thread([&] {
+        std::unique_lock guard(m);
+        EXPECT_FALSE(flag);
+        waiting.store(true, std::memory_order_relaxed);
+        cv.wait(guard, [&] { return flag; });
+        EXPECT_TRUE(flag);
+    });
+
+    while (!waiting.load(std::memory_order_relaxed)) {
+        std::this_thread::yield();
+    }
+    {
+        std::unique_lock guard(m);
+        flag = true;
+        cv.notify_all();
+    }
+
+    thread.join();
+}
+
+TYPED_TEST(ConditionVariableTest, WaitPredicateAll) {
+    using CVUnderTest = TypeParam;
+
+    bool flag = false;
+    std::mutex m;
+    CVUnderTest cv;
+
+    std::atomic<size_t> waiting = 0;
+    std_support::vector<ScopedThread> threads;
+    for (int i = 0; i < kDefaultThreadCount; ++i) {
+        threads.emplace_back([&] {
+            std::unique_lock guard(m);
+            EXPECT_FALSE(flag);
+            waiting.fetch_add(1, std::memory_order_relaxed);
+            cv.wait(guard, [&] { return flag; });
+            EXPECT_TRUE(flag);
+        });
+    }
+
+    while (waiting.load(std::memory_order_relaxed) != threads.size()) {
+        std::this_thread::yield();
+    }
+    {
+        std::unique_lock guard(m);
+        flag = true;
+    }
+    cv.notify_all();
+
+    threads.clear();
+}
+
+TYPED_TEST(ConditionVariableTest, WaitPredicateAllNotifyUnderLock) {
+    using CVUnderTest = TypeParam;
+
+    bool flag = false;
+    std::mutex m;
+    CVUnderTest cv;
+
+    std::atomic<size_t> waiting = 0;
+    std_support::vector<ScopedThread> threads;
+    for (int i = 0; i < kDefaultThreadCount; ++i) {
+        threads.emplace_back([&] {
+            std::unique_lock guard(m);
+            EXPECT_FALSE(flag);
+            waiting.fetch_add(1, std::memory_order_relaxed);
+            cv.wait(guard, [&] { return flag; });
+            EXPECT_TRUE(flag);
+        });
+    }
+
+    while (waiting.load(std::memory_order_relaxed) != threads.size()) {
+        std::this_thread::yield();
+    }
+    {
+        std::unique_lock guard(m);
+        flag = true;
+        cv.notify_all();
+    }
+
+    threads.clear();
+}
+
+TYPED_TEST(ConditionVariableTest, Checkpoint) {
+    constexpr uint64_t epochsCount = 1000;
+    using CVUnderTest = TypeParam;
+
+    uint64_t epochScheduled = 0;
+    uint64_t epochStarted = 0;
+    uint64_t epochFinished = 0;
+    std::mutex m;
+    CVUnderTest cv;
+
+    auto schedule = [&] {
+        std::unique_lock guard(m);
+        if (epochScheduled > epochStarted) {
+            return epochScheduled;
+        }
+        epochScheduled = epochStarted + 1;
+        return epochScheduled;
+    };
+
+    std_support::vector<ScopedThread> threads;
+    std::array<std::atomic<uint64_t>, kDefaultThreadCount> checkpoints = {0};
+    for (int i = 0; i < kDefaultThreadCount; ++i) {
+        threads.emplace_back([&, i] {
+            while (true) {
+                uint64_t epoch = schedule();
+                if (epoch >= epochsCount) return;
+                {
+                    std::unique_lock guard(m);
+                    if (epochFinished < epoch) {
+                        checkpoints[i].store(2 * epoch, std::memory_order_relaxed);
+                        cv.wait(guard, [&] { return epochFinished >= epoch; });
+                        checkpoints[i].store(2 * epoch + 1, std::memory_order_relaxed);
+                    }
+                }
+            }
+        });
+    }
+
+    while (epochStarted <= epochsCount) {
+        {
+            std::unique_lock guard(m);
+            ++epochStarted;
+        }
+        std::this_thread::yield();
+        {
+            std::unique_lock guard(m);
+            epochFinished = epochStarted;
+        }
+        cv.notify_all();
+        for (auto& checkpoint : checkpoints) {
+            while (true) {
+                auto value = checkpoint.load(std::memory_order_relaxed);
+                auto epoch = value / 2;
+                bool isWaiting = value % 2 == 0;
+                if (epoch > epochFinished) break;
+                if (!isWaiting) break;
+                std::this_thread::yield();
+            }
+        }
+    }
+    threads.clear();
+}