From c12c1ec61663fc9bd460fea698361b41afb6e9d1 Mon Sep 17 00:00:00 2001
From: Daniel Frey <d.frey@gmx.de>
Date: Sat, 2 Mar 2024 00:23:04 +0100
Subject: [PATCH] Add example for size-limited connection pools, see #72

---
 src/test/pq/connection_pool.cpp | 73 +++++++++++++++++++++++++++++----
 1 file changed, 64 insertions(+), 9 deletions(-)

diff --git a/src/test/pq/connection_pool.cpp b/src/test/pq/connection_pool.cpp
index d2a47ae..028ed44 100644
--- a/src/test/pq/connection_pool.cpp
+++ b/src/test/pq/connection_pool.cpp
@@ -7,25 +7,80 @@
 
 #include <tao/pq/connection_pool.hpp>
 
+class limited_connection_pool
+   : public tao::pq::connection_pool
+{
+   using tao::pq::connection_pool::connection_pool;
+
+   [[nodiscard]] auto v_create() const -> std::unique_ptr< tao::pq::connection > override
+   {
+      if( attached() >= 4 ) {
+         throw std::runtime_error( "connection limit reached" );
+      }
+      return connection_pool::v_create();
+   }
+};
+
 void run()
 {
    // overwrite the default with an environment variable if needed
    const auto connection_string = tao::pq::internal::getenv( "TAOPQ_TEST_DATABASE", "dbname=template1" );
 
-   const auto pool = tao::pq::connection_pool::create( connection_string );
+   const auto pool = tao::pq::connection_pool::create< limited_connection_pool >( connection_string );
+
+   TEST_ASSERT( pool->empty() );
+   TEST_ASSERT( pool->size() == 0 );
+   TEST_ASSERT( pool->attached() == 0 );
 
    TEST_ASSERT( pool->connection() );
+
+   TEST_ASSERT( !pool->empty() );
+   TEST_ASSERT( pool->size() == 1 );
+   TEST_ASSERT( pool->attached() == 0 );
+
    TEST_ASSERT( pool->connection()->execute( "SELECT 1" ).as< int >() == 1 );
 
-   const auto conn = pool->connection();
-   TEST_ASSERT( pool->connection() );
-   TEST_ASSERT( conn->execute( "SELECT 2" ).as< int >() == 2 );
+   TEST_ASSERT( pool->size() == 1 );
+   TEST_ASSERT( pool->attached() == 0 );
 
-   const auto pool2 = tao::pq::connection_pool::create( connection_string );
-   TEST_ASSERT( pool->connection()->execute( "SELECT 3" ).as< int >() == 3 );
-   TEST_ASSERT( pool2->connection()->execute( "SELECT 4" ).as< int >() == 4 );
-   TEST_ASSERT( conn->execute( "SELECT 5" ).as< int >() == 5 );
-   TEST_ASSERT( pool2->connection()->execute( "SELECT 6" ).as< int >() == 6 );
+   {
+      const auto conn = pool->connection();
+      TEST_ASSERT( pool->connection() );
+      TEST_ASSERT( conn->execute( "SELECT 2" ).as< int >() == 2 );
+
+      TEST_ASSERT( pool->size() == 1 );
+      TEST_ASSERT( pool->attached() == 1 );
+
+      const auto pool2 = tao::pq::connection_pool::create( connection_string );
+      TEST_ASSERT( pool->connection()->execute( "SELECT 3" ).as< int >() == 3 );
+      TEST_ASSERT( pool2->connection()->execute( "SELECT 4" ).as< int >() == 4 );
+      TEST_ASSERT( conn->execute( "SELECT 5" ).as< int >() == 5 );
+      TEST_ASSERT( pool2->connection()->execute( "SELECT 6" ).as< int >() == 6 );
+   }
+
+   TEST_ASSERT( pool->size() == 2 );
+   TEST_ASSERT( pool->attached() == 0 );
+   {
+      const auto c0 = pool->connection();
+      const auto c1 = pool->connection();
+      TEST_ASSERT( pool->size() == 0 );
+      TEST_ASSERT( pool->attached() == 2 );
+      {
+         const auto c2 = pool->connection();
+         const auto c3 = pool->connection();
+         TEST_ASSERT( pool->size() == 0 );
+         TEST_ASSERT( pool->attached() == 4 );
+
+         TEST_THROWS( pool->connection() );
+
+         TEST_ASSERT( pool->size() == 0 );
+         TEST_ASSERT( pool->attached() == 4 );
+      }
+      TEST_ASSERT( pool->size() == 2 );
+      TEST_ASSERT( pool->attached() == 2 );
+   }
+   TEST_ASSERT( pool->size() == 4 );
+   TEST_ASSERT( pool->attached() == 0 );
 }
 
 auto main() -> int  // NOLINT(bugprone-exception-escape)