ChatGPT 3.5 生成的 Delphi DBExpress 連接池

當使用 Delphi DBExpress 進行數據庫連接時，可以使用 TSQLConnection 組件來實現連接池。下面是一個簡單的示例代碼，演示瞭如何創建一個基本的連接池： 

unit uDBConnectionPool;

interface

uses
  SysUtils, Classes, DB, SqlExpr, SyncObjs;

type
  TDBConnectionPool = class
  private
    FConnections: TList;
    FMaxConnections: Integer;
    FSQLConnection: TSQLConnection;
    FCriticalSection: TCriticalSection;
  public
    constructor Create(SQLConnection: TSQLConnection; MaxConnections: Integer);
    destructor Destroy; override;
    function GetConnection: TSQLConnection;
    procedure ReleaseConnection(Connection: TSQLConnection);
  end;

implementation

constructor TDBConnectionPool.Create(SQLConnection: TSQLConnection; MaxConnections: Integer);
var
  i: Integer;
begin
  FConnections := TList.Create;
  FMaxConnections := MaxConnections;
  FSQLConnection := SQLConnection;
  for i := 1 to MaxConnections do
  begin
    FConnections.Add(TSQLConnection.Create(nil));
  end;
  FCriticalSection := TCriticalSection.Create;
end;

destructor TDBConnectionPool.Destroy;
var
  i: Integer;
begin
  for i := 0 to FConnections.Count - 1 do
  begin
    TSQLConnection(FConnections[i]).Free;
  end;
  FConnections.Free;
  FCriticalSection.Free;
  inherited;
end;

function TDBConnectionPool.GetConnection: TSQLConnection;
begin
  FCriticalSection.Enter;
  try
    if FConnections.Count > 0 then
    begin
      Result := TSQLConnection(FConnections[FConnections.Count - 1]);
      FConnections.Delete(FConnections.Count - 1);
    end
    else
    begin
      Result := TSQLConnection.Create(nil);
      Result.SQLConnection := FSQLConnection;
    end;
  finally
    FCriticalSection.Leave;
  end;
end;

procedure TDBConnectionPool.ReleaseConnection(Connection: TSQLConnection);
begin
  FCriticalSection.Enter;
  try
    if FConnections.Count < FMaxConnections then
    begin
      FConnections.Add(Connection);
    end
    else
    begin
      Connection.Free;
    end;
  finally
    FCriticalSection.Leave;
  end;
end;

end.

在這個示例代碼中，我們創建了一個 TDBConnectionPool 類，它包含了一個 TList 用於存儲連接對象，使用 TCriticalSection 進行線程同步。在創建連接池時，我們初始化一定數量的連接對象，並在需要連接時從連接池中獲取連接，使用完畢後釋放連接。

這是一個基礎的示例，實際的連接池可能還需要添加更多功能，例如連接的有效性檢查、超時處理等。希望這個示例能夠幫助你實現你自己的 Delphi DBExpress 連接池。