From 93b868aaafecdee525098a760dcf385a6c2ba3e2 Mon Sep 17 00:00:00 2001
From: Sascha Kuehl <skuehl1972@gmail.com>
Date: Mon, 27 Nov 2023 17:26:14 +0100
Subject: [PATCH] enhanced connection pool of unique id for each connection

---
 include/matador/sql/connection_pool.hpp | 83 ++++++++++++++++++-------
 test/ConnectionPoolTest.cpp             |  3 +-
 2 files changed, 61 insertions(+), 25 deletions(-)

diff --git a/include/matador/sql/connection_pool.hpp b/include/matador/sql/connection_pool.hpp
index e3f9c95..3e7b6f4 100644
--- a/include/matador/sql/connection_pool.hpp
+++ b/include/matador/sql/connection_pool.hpp
@@ -5,6 +5,7 @@
 #include <queue>
 #include <mutex>
 #include <string>
+#include <unordered_map>
 #include <unordered_set>
 
 namespace matador::sql {
@@ -12,64 +13,98 @@ namespace matador::sql {
 template < class Connection >
 class connection_pool;
 
+template < class Connection >
+using IdConnection = std::pair<size_t, Connection>;
+
 template < class Connection >
 class connection_ptr
 {
 public:
-  connection_ptr(Connection *c, connection_pool<Connection> &pool)
+  connection_ptr(IdConnection<Connection> *c, connection_pool<Connection> &pool)
   : connection_(c), pool_(pool) {}
   ~connection_ptr();
   connection_ptr(const connection_ptr &) = delete;
   connection_ptr& operator=(const connection_ptr &) = delete;
-  connection_ptr(connection_ptr &&) noexcept = default;
-  connection_ptr& operator=(connection_ptr &&) noexcept = default;
+  connection_ptr(connection_ptr &&x) noexcept
+  : connection_(x.connection_)
+  , pool_(x.pool_)
+  {
+    x.connection_ = nullptr;
+  }
+  connection_ptr& operator=(connection_ptr &&x) noexcept
+  {
+    if (this == &x) {
+      return *this;
+    }
+    connection_ = x.connection_;
+    pool_ = x.pool_;
+    x.connection_ = nullptr;
 
-  Connection* operator->() { return connection_; }
-  Connection& operator*() { return *connection_; }
+    return *this;
+  }
+
+  Connection* operator->() { return &connection_->second; }
+  Connection& operator*() { return connection_->second; }
+
+  [[nodiscard]] size_t id() const { return connection_->first; }
 
   [[nodiscard]] bool valid() const { return connection_ != nullptr; }
 
 private:
   friend class connection_pool<Connection>;
 
-  Connection *connection_;
+  IdConnection<Connection> *connection_;
   connection_pool<Connection> &pool_;
 };
 
 template < class Connection >
 class connection_pool
 {
+public:
+  using connection_pointer = connection_ptr<Connection>;
+
 public:
   connection_pool(const std::string &dns, unsigned int count)
   : info_(connection_info::parse(dns)) {
     connection_repo_.reserve(count);
     for (auto i = 0U; i < count; ++i) {
-      connection_repo_.emplace_back(info_);
-      idle_connections_.push(&connection_repo_.back());
-      idle_connections_.back()->open();
+      connection_repo_.emplace_back(i+1, info_);
+      auto &conn = connection_repo_.back();
+      idle_connections_.emplace(conn.first, &conn);
+      conn.second.open();
     }
   }
 
   connection_ptr<Connection> acquire() {
-    std::lock_guard<std::mutex> guard(mutex_);
+    std::unique_lock<std::mutex> lock(mutex_);
     if (idle_connections_.empty()) {
       return {nullptr, *this};
     }
 
-    auto ptr = idle_connections_.front();
-    idle_connections_.pop();
-    inuse_connections_.insert(ptr);
-    return { ptr, *this };
+
+    pointer next_connection{nullptr};
+    for (auto &item : idle_connections_) {
+      next_connection = item.second;
+      auto node = idle_connections_.extract(item.first);
+      inuse_connections_.insert(std::move(node));
+      break;
+    }
+    return {next_connection, *this};
   }
 
-  void release(Connection *c) {
+  connection_ptr<Connection> acquire(size_t id) {
+    std::lock_guard<std::mutex> guard(mutex_);
+    return {nullptr, *this};
+  }
+
+  void release(IdConnection<Connection> *c) {
     if (c == nullptr) {
       return;
     }
-    std::lock_guard<std::mutex> guard(mutex_);
-
-    if (inuse_connections_.erase(c) > 0) {
-      idle_connections_.push(c);
+    std::unique_lock<std::mutex> lock(mutex_);
+    if (auto it = inuse_connections_.find(c->first); it != inuse_connections_.end()) {
+      auto node = inuse_connections_.extract(it);
+      idle_connections_.insert(std::move(node));
     }
   }
 
@@ -93,12 +128,14 @@ public:
   }
 private:
   mutable std::mutex mutex_;
-  std::vector<Connection> connection_repo_;
-  using pointer = Connection*;
+  std::vector<IdConnection<Connection>> connection_repo_;
+  using pointer = IdConnection<Connection>*;
   using connections = std::queue<pointer>;
+  using connection_map = std::unordered_map<size_t, pointer>;
   using connection_set = std::unordered_set<pointer>;
-  connections idle_connections_;
-  connection_set inuse_connections_;
+//  connections idle_connections_;
+  connection_map inuse_connections_;
+  connection_map idle_connections_;
 
   const connection_info info_;
 };
diff --git a/test/ConnectionPoolTest.cpp b/test/ConnectionPoolTest.cpp
index 6aa600e..88b0f34 100644
--- a/test/ConnectionPoolTest.cpp
+++ b/test/ConnectionPoolTest.cpp
@@ -16,8 +16,8 @@ TEST_CASE("Create connection pool", "[connection pool]") {
 
   auto ptr = pool.acquire();
   REQUIRE(ptr.valid());
+  REQUIRE(ptr.id() > 0);
   REQUIRE(ptr->is_open());
-//  REQUIRE(!ptr->dns().empty());
 
   REQUIRE(pool.idle() == 3);
   REQUIRE(pool.inuse() == 1);
@@ -31,7 +31,6 @@ TEST_CASE("Create connection pool", "[connection pool]") {
     auto ptr2 = pool.acquire();
     REQUIRE(ptr2.valid());
     REQUIRE(ptr2->is_open());
-//    REQUIRE(!ptr2->dns().empty());
 
     REQUIRE(pool.idle() == 3);
     REQUIRE(pool.inuse() == 1);