parallel fixes and benchmark update

CMakeLists.txt

@@ -6,4 +6,5 @@ set(CMAKE_CXX_STANDARD 20)
 add_executable(parallelUnorderedMap main.cpp
         UnorderedParallelMap.h
         optimization.h
-        UnorderedParallelMap.cpp)
+        UnorderedParallelMap.cpp
+)

UnorderedParallelMap.h

@@ -1,365 +1,367 @@
 #ifndef UNORDEREDPARALLELMAP_H
 #define UNORDEREDPARALLELMAP_H
 
-#include <memory>
-#include <atomic>
 #include <vector>
 #include <optional>
-#include <thread>
+#include <shared_mutex>
+#include <atomic>
+#include <functional>
+#include <cstdint>
 #include "optimization.h"
 
 template <typename K, typename V>
 class LockFreeMap
 {
-private:
-    struct Bucket
+    static_assert(std::is_trivially_copyable_v<K>);
+    static_assert(std::is_trivially_copyable_v<V>);
+
+    struct Entry
     {
-        std::atomic<bool> occupied{false};
-        std::atomic<bool> deleted{false};
-        std::atomic<K> key;
-        std::atomic<V> value;
-        std::atomic<Bucket*> next{nullptr};
+        std::atomic<uint64_t> version{0}; // even: stable, odd: writing
+        bool occupied = false;
+        bool deleted = false;
+        K key{};
+        V value{};
     };
 
-    struct Table
-    {
-        size_t capacity;
-        std::vector<Bucket> buckets;
+    std::vector<Entry> buckets;
+    mutable std::shared_mutex resize_mutex;
+    std::atomic<size_t> count{0};
+    size_t capacity;
+    static constexpr float MAX_LOAD = 0.7;
 
-        explicit Table(size_t cap) : capacity(cap), buckets(cap)
-        {
-        }
-    };
-
-    std::shared_ptr<Table> table;
-    std::shared_ptr<Table> new_table{nullptr};
-    std::atomic<size_t> size_counter{0};
-    std::mutex resize_mutex;
-    static constexpr float MAX_LOAD_FACTOR = 0.75;
-
-    size_t hash(const K& key, size_t capacity) const
+    size_t hash(const K& key) const
     {
         return std::hash<K>{}(key) % capacity;
     }
 
-    void migrate_entry(Bucket& src, const std::shared_ptr<Table>& dest)
+    size_t probe(size_t h, size_t i) const
     {
-        if (!src.occupied.load() || src.deleted.load()) return;
+        return (h + i) % capacity;
+    }
 
-        const K key = src.key.load();
-        const V val = src.value.load();
-        size_t idx = hash(key, dest->capacity);
-        Bucket& head = dest->buckets[idx];
+    void resize()
+    {
+        size_t new_capacity = capacity * 2;
+        std::vector<Entry> new_buckets(new_capacity);
 
-        if (!head.occupied.load())
+        for (auto& e : buckets)
         {
-            bool expected = false;
-            if (head.occupied.compare_exchange_strong(expected, true))
+            prefetch_for_read(&e);
+            cpu_relax();
+
+            if (e.occupied && !e.deleted)
             {
-                head.key.store(key);
-                head.value.store(val);
-                head.deleted.store(false);
-                return;
+                size_t h = std::hash<K>{}(e.key) % new_capacity;
+                for (size_t i = 0; i < new_capacity; ++i)
+                {
+                    size_t idx = (h + i) % new_capacity;
+                    Entry& ne = new_buckets[idx];
+                    prefetch_for_write(&ne);
+                    cpu_relax();
+
+                    if (!ne.occupied)
+                    {
+                        ne.version.store(1);
+                        ne.key = e.key;
+                        ne.value = e.value;
+                        ne.occupied = true;
+                        ne.deleted = false;
+                        ne.version.store(2);
+                        break;
+                    }
+                }
             }
         }
 
-        Bucket* current = &head;
-        while (true)
-        {
-            if (!current->deleted.load() && current->key.load() == key)
-                return;
-
-            Bucket* next = current->next.load();
-            if (next)
-            {
-                current = next;
-            }
-            else
-            {
-                Bucket* new_node = new Bucket;
-                new_node->occupied.store(true);
-                new_node->key.store(key);
-                new_node->value.store(val);
-                new_node->deleted.store(false);
-                if (current->next.compare_exchange_strong(next, new_node))
-                    return;
-                delete new_node;
-            }
-        }
-    }
-
-    void start_resize(size_t new_capacity)
-    {
-        std::lock_guard<std::mutex> lock(resize_mutex);
-        if (new_table) return;
-
-        auto old_table = table;
-        auto next = std::make_shared<Table>(new_capacity);
-        new_table = next;
-
-        std::thread([this, old_table, next]()
-        {
-            for (auto& bucket : old_table->buckets)
-            {
-                Bucket* current = &bucket;
-                while (current)
-                {
-                    migrate_entry(*current, next);
-                    current = current->next.load();
-                }
-            }
-            table = next;
-            new_table = nullptr;
-
-            for (auto& bucket : old_table->buckets)
-            {
-                Bucket* current = bucket.next.load();
-                while (current)
-                {
-                    Bucket* next = current->next.load();
-                    delete current;
-                    current = next;
-                }
-            }
-        }).detach();
-    }
-
-    std::shared_ptr<Table> active_table() const
-    {
-        auto nt = new_table;
-        return nt ? nt : table;
+        buckets = std::move(new_buckets);
+        capacity = new_capacity;
     }
 
 public:
-    explicit LockFreeMap(size_t initial_capacity = 1024)
+    explicit LockFreeMap(size_t init_cap = 1024)
+        : buckets(init_cap), capacity(init_cap)
     {
-        table = std::make_shared<Table>(initial_capacity);
     }
 
-    ~LockFreeMap()
+    bool insert(const K& key, const V& val)
     {
-        auto t = table;
-        for (auto& bucket : t->buckets)
+        std::unique_lock lock(resize_mutex);
+
+        if ((float)(count.load() + 1) / capacity > MAX_LOAD)
+            resize();
+
+        size_t h = hash(key);
+        for (size_t i = 0; i < capacity; ++i)
         {
-            Bucket* current = bucket.next.load();
-            while (current)
+            size_t idx = probe(h, i);
+            Entry& e = buckets[idx];
+
+            prefetch_for_write(&e);
+            cpu_relax();
+
+            if (!e.occupied || (e.deleted && e.key == key))
             {
-                Bucket* next = current->next.load();
-                delete current;
-                current = next;
-            }
-        }
-    }
+                uint64_t v = e.version.load();
+                if (v % 2 != 0) continue;
 
-    bool insert(const K& key, const V& value)
-    {
-        if ((float)(size_counter.load() + 1) / table->capacity > MAX_LOAD_FACTOR)
-            start_resize(table->capacity * 2);
-
-        auto t = active_table();
-        size_t idx = hash(key, t->capacity);
-        Bucket& head = t->buckets[idx];
-        prefetch_for_read(&head);
-
-        if (!head.occupied.load())
-        {
-            bool expected = false;
-            if (head.occupied.compare_exchange_strong(expected, true))
-            {
-                head.key.store(key);
-                head.value.store(value);
-                head.deleted.store(false);
-                size_counter.fetch_add(1);
-                return true;
-            }
-        }
-
-        Bucket* current = &head;
-        while (true)
-        {
-            if (!current->deleted.load() && current->key.load() == key)
-                return false;
-
-            Bucket* next = current->next.load();
-            if (next)
-            {
-                current = next;
-                cpu_relax();
-            }
-            else
-            {
-                Bucket* new_node = new Bucket;
-                new_node->occupied.store(true);
-                new_node->key.store(key);
-                new_node->value.store(value);
-                new_node->deleted.store(false);
-                if (current->next.compare_exchange_strong(next, new_node))
+                if (e.version.compare_exchange_strong(v, v + 1))
                 {
-                    size_counter.fetch_add(1);
+                    e.key = key;
+                    e.value = val;
+                    e.occupied = true;
+                    e.deleted = false;
+                    e.version.store(v + 2);
+                    count.fetch_add(1);
                     return true;
                 }
-                delete new_node;
-                cpu_relax();
+                --i;
+            }
+            else if (!e.deleted && e.key == key)
+            {
+                return false;
             }
         }
+        return false;
     }
 
-    std::optional<V> find(const K& key)
+    std::optional<V> find(const K& key) const
     {
-        auto t = active_table();
-        size_t idx = hash(key, t->capacity);
-        Bucket* current = &t->buckets[idx];
-
-        while (current)
+        size_t h = hash(key);
+        for (size_t i = 0; i < capacity; ++i)
         {
-            if (current->occupied.load() &&
-                !current->deleted.load() &&
-                current->key.load() == key)
-            {
-                return current->value.load();
-            }
-            current = current->next.load();
-            cpu_relax();
-        }
+            size_t idx = probe(h, i);
+            const Entry& e = buckets[idx];
 
+            prefetch_for_read(&e);
+            cpu_relax();
+
+            uint64_t v1 = e.version.load(std::memory_order_acquire);
+            if (v1 % 2 != 0) continue;
+
+            if (e.occupied && !e.deleted && e.key == key)
+            {
+                V val = e.value;
+                cpu_relax();
+                uint64_t v2 = e.version.load(std::memory_order_acquire);
+                if (v1 == v2 && v2 % 2 == 0)
+                    return val;
+            }
+        }
         return std::nullopt;
     }
 
     bool erase(const K& key)
     {
-        auto t = active_table();
-        size_t idx = hash(key, t->capacity);
-        Bucket* current = &t->buckets[idx];
+        std::unique_lock lock(resize_mutex);
 
-        while (current)
+        size_t h = hash(key);
+        for (size_t i = 0; i < capacity; ++i)
         {
-            if (current->occupied.load() &&
-                !current->deleted.load() &&
-                current->key.load() == key)
-            {
-                current->deleted.store(true);
-                size_counter.fetch_sub(1);
-                return true;
-            }
-            current = current->next.load();
-            cpu_relax();
-        }
+            size_t idx = probe(h, i);
+            Entry& e = buckets[idx];
 
+            prefetch_for_write(&e);
+            cpu_relax();
+
+            if (e.occupied && !e.deleted && e.key == key)
+            {
+                uint64_t v = e.version.load();
+                if (v % 2 != 0) continue;
+
+                if (e.version.compare_exchange_strong(v, v + 1))
+                {
+                    e.deleted = true;
+                    e.version.store(v + 2);
+                    count.fetch_sub(1);
+                    return true;
+                }
+                --i;
+            }
+        }
         return false;
     }
 
-    bool update(const K& key, const V& new_value)
+    bool update(const K& key, const V& new_val)
     {
-        auto t = active_table();
-        size_t idx = hash(key, t->capacity);
-        Bucket* current = &t->buckets[idx];
-
-        while (current)
+        size_t h = hash(key);
+        for (size_t i = 0; i < capacity; ++i)
         {
-            if (current->occupied.load() &&
-                !current->deleted.load() &&
-                current->key.load() == key)
-            {
-                current->value.store(new_value);
-                return true;
-            }
-            current = current->next.load();
-            cpu_relax();
-        }
+            size_t idx = probe(h, i);
+            Entry& e = buckets[idx];
 
+            prefetch_for_write(&e);
+            cpu_relax();
+
+            uint64_t v = e.version.load();
+            if (v % 2 != 0) continue;
+
+            if (e.occupied && !e.deleted && e.key == key)
+            {
+                if (e.version.compare_exchange_strong(v, v + 1))
+                {
+                    e.value = new_val;
+                    e.version.store(v + 2);
+                    return true;
+                }
+                --i;
+            }
+        }
         return false;
     }
 
-    void shrink()
+    std::vector<K> keys() const
     {
-        size_t current_size = size_counter.load();
-        auto cap = table->capacity;
-        if (current_size < cap / 4 && cap > 1024)
-            start_resize(cap / 2);
+        std::vector<K> result;
+        for (const auto& e : buckets)
+        {
+            prefetch_for_read(&e);
+            cpu_relax();
+
+            uint64_t v1 = e.version.load(std::memory_order_acquire);
+            if (v1 % 2 != 0 || !e.occupied || e.deleted) continue;
+
+            K key = e.key;
+            cpu_relax();
+            uint64_t v2 = e.version.load(std::memory_order_acquire);
+            if (v1 == v2 && v2 % 2 == 0)
+                result.push_back(key);
+        }
+        return result;
+    }
+
+    std::vector<std::pair<K, V>> entries() const
+    {
+        std::vector<std::pair<K, V>> result;
+        for (const auto& e : buckets)
+        {
+            prefetch_for_read(&e);
+            cpu_relax();
+
+            uint64_t v1 = e.version.load(std::memory_order_acquire);
+            if (v1 % 2 != 0 || !e.occupied || e.deleted) continue;
+
+            K key = e.key;
+            V val = e.value;
+            cpu_relax();
+            uint64_t v2 = e.version.load(std::memory_order_acquire);
+            if (v1 == v2 && v2 % 2 == 0)
+                result.emplace_back(key, val);
+        }
+        return result;
+    }
+
+    void for_each(const std::function<void(const K&, const V&)>& cb) const
+    {
+        for (const auto& e : buckets)
+        {
+            prefetch_for_read(&e);
+            cpu_relax();
+
+            uint64_t v1 = e.version.load(std::memory_order_acquire);
+            if (v1 % 2 != 0 || !e.occupied || e.deleted) continue;
+
+            K key = e.key;
+            V val = e.value;
+            cpu_relax();
+            uint64_t v2 = e.version.load(std::memory_order_acquire);
+            if (v1 == v2 && v2 % 2 == 0)
+                cb(key, val);
+        }
+    }
+
+    void for_each_mut(const std::function<void(const K&, V&)>& cb)
+    {
+        for (auto& e : buckets)
+        {
+            prefetch_for_write(&e);
+            cpu_relax();
+
+            if (!e.occupied || e.deleted) continue;
+
+            uint64_t v = e.version.load();
+            if (v % 2 != 0) continue;
+
+            if (e.version.compare_exchange_strong(v, v + 1))
+            {
+                cb(e.key, e.value);
+                e.version.store(v + 2);
+            }
+            else
+            {
+                cpu_relax();
+            }
+        }
+    }
+
+    void clear()
+    {
+        std::unique_lock lock(resize_mutex);
+
+        for (auto& e : buckets)
+        {
+            prefetch_for_write(&e);
+            cpu_relax();
+
+            uint64_t v = e.version.load();
+            if (v % 2 != 0) continue;
+
+            if (e.version.compare_exchange_strong(v, v + 1))
+            {
+                e.occupied = false;
+                e.deleted = false;
+                e.version.store(v + 2);
+            }
+        }
+        count.store(0);
+    }
+
+    void reserve(size_t desired_capacity)
+    {
+        std::unique_lock lock(resize_mutex);
+        if (desired_capacity <= capacity) return;
+
+        size_t new_capacity = 1;
+        while (new_capacity < desired_capacity) new_capacity <<= 1;
+
+        std::vector<Entry> new_buckets(new_capacity);
+
+        for (auto& e : buckets)
+        {
+            prefetch_for_read(&e);
+            cpu_relax();
+
+            if (e.occupied && !e.deleted)
+            {
+                size_t h = std::hash<K>{}(e.key) % new_capacity;
+                for (size_t i = 0; i < new_capacity; ++i)
+                {
+                    size_t idx = (h + i) % new_capacity;
+                    Entry& ne = new_buckets[idx];
+                    prefetch_for_write(&ne);
+                    cpu_relax();
+
+                    if (!ne.occupied)
+                    {
+                        ne.version.store(1);
+                        ne.key = e.key;
+                        ne.value = e.value;
+                        ne.occupied = true;
+                        ne.deleted = false;
+                        ne.version.store(2);
+                        break;
+                    }
+                }
+            }
+        }
+
+        buckets = std::move(new_buckets);
+        capacity = new_capacity;
     }
 
     size_t size() const
     {
-        return size_counter.load();
-    }
-
-    bool rehash_one(const K& key)
-    {
-        auto src = table;
-        auto dst = new_table;
-        if (!dst) return false;
-
-        size_t idx = hash(key, src->capacity);
-        Bucket* current = &src->buckets[idx];
-
-        while (current)
-        {
-            if (current->occupied.load() &&
-                !current->deleted.load() &&
-                current->key.load() == key)
-            {
-                migrate_entry(*current, dst);
-                return true;
-            }
-            current = current->next.load();
-        }
-        return false;
-    }
-
-    std::vector<K> keys()
-    {
-        std::vector<K> result;
-        auto t = active_table();
-        for (auto& bucket : t->buckets)
-        {
-            Bucket* current = &bucket;
-            while (current)
-            {
-                if (current->occupied.load() &&
-                    !current->deleted.load())
-                {
-                    result.push_back(current->key.load());
-                }
-                current = current->next.load();
-            }
-        }
-        return result;
-    }
-
-    std::vector<std::pair<K, V>> entries()
-    {
-        std::vector<std::pair<K, V>> result;
-        auto t = active_table();
-        for (auto& bucket : t->buckets)
-        {
-            Bucket* current = &bucket;
-            while (current)
-            {
-                if (current->occupied.load() && !current->deleted.load())
-                {
-                    result.emplace_back(current->key.load(), current->value.load());
-                }
-                current = current->next.load();
-            }
-        }
-        return result;
-    }
-
-    void for_each(const std::function<void(const K&, const V&)>& cb)
-    {
-        auto t = active_table();
-        for (auto& bucket : t->buckets)
-        {
-            Bucket* current = &bucket;
-            while (current)
-            {
-                if (current->occupied.load() && !current->deleted.load())
-                {
-                    cb(current->key.load(), current->value.load());
-                }
-                current = current->next.load();
-            }
-        }
+        return count.load();
     }
 };
 

main.cpp

@@ -1,13 +1,25 @@
 #include <cassert>
 #include <iostream>
 #include <map>
-
-#include "UnorderedParallelMap.h"
+#include <thread>
 #include <random>
+#include <chrono>
+#include <atomic>
+#include "UnorderedParallelMap.h"
 
 constexpr int THREADS = 8;
 constexpr int OPS_PER_THREAD = 10000;
 
+std::atomic<uint64_t> insert_ns{0};
+std::atomic<uint64_t> find_ns{0};
+std::atomic<uint64_t> update_ns{0};
+std::atomic<uint64_t> erase_ns{0};
+
+inline uint64_t now_ns() {
+    return std::chrono::duration_cast<std::chrono::nanoseconds>(
+        std::chrono::steady_clock::now().time_since_epoch()).count();
+}
+
 void worker(LockFreeMap<int, int>& map, int thread_id)
 {
     std::mt19937 rng(thread_id);
@@ -19,19 +31,25 @@ void worker(LockFreeMap<int, int>& map, int thread_id)
         int key = dist(rng);
         int value = thread_id * 1000 + i;
 
+        uint64_t start = now_ns();
+
         switch (op)
         {
         case 0:
             map.insert(key, value);
+            insert_ns += (now_ns() - start);
             break;
         case 1:
             map.find(key);
+            find_ns += (now_ns() - start);
             break;
         case 2:
             map.update(key, value + 1);
+            update_ns += (now_ns() - start);
             break;
         case 3:
             map.erase(key);
+            erase_ns += (now_ns() - start);
             break;
         }
     }
@@ -61,25 +79,40 @@ int main()
     simple_test_map.insert(1, 1);
     simple_test_map.insert(2, 44);
     assert(simple_test_map.size() == 2);
-    assert(simple_test_map.find(2) == 44);
+    assert(simple_test_map.find(2).value_or(-1) == 44);
     simple_test_map.update(2, 55);
-    assert(simple_test_map.find(2) == 55);
+    assert(simple_test_map.find(2).value_or(-1) == 55);
     std::cout << "✓ Single-thread test finished\n" << std::endl;
     verify_map(simple_test_map);
 
     LockFreeMap<int, int> map(1024);
-
     std::vector<std::thread> threads;
     threads.reserve(THREADS);
+
+    auto start_total = std::chrono::steady_clock::now();
+
     for (int i = 0; i < THREADS; ++i)
         threads.emplace_back(worker, std::ref(map), i);
 
     for (auto& t : threads)
         t.join();
 
+    auto end_total = std::chrono::steady_clock::now();
+    auto total_ns = std::chrono::duration_cast<std::chrono::nanoseconds>(end_total - start_total).count();
+
     std::cout << "✓ Multi-thread test finished\n" << std::endl;
 
     verify_map(map);
 
+    uint64_t total_ops = THREADS * OPS_PER_THREAD;
+    std::cout << "--- Benchmark Results ---\n";
+    std::cout << "Total ops:      " << total_ops << "\n";
+    std::cout << "Total time:     " << total_ns / 1e6 << " ms\n";
+    std::cout << "Insert avg:     " << insert_ns / 1e3 << " μs total (" << (insert_ns / (double)total_ops) << " ns/op)\n";
+    std::cout << "Find avg:       " << find_ns / 1e3 << " μs total (" << (find_ns / (double)total_ops) << " ns/op)\n";
+    std::cout << "Update avg:     " << update_ns / 1e3 << " μs total (" << (update_ns / (double)total_ops) << " ns/op)\n";
+    std::cout << "Erase avg:      " << erase_ns / 1e3 << " μs total (" << (erase_ns / (double)total_ops) << " ns/op)\n";
+    std::cout << "--------------------------\n";
+
     return 0;
 }