垃圾收集与删除文件

有时候在程序中需要删除某个文件,却出现"文件由另一个进程使用,不能删除"的错误,这往往是因为文件句柄资源没有关闭. 在C#中关闭句柄后有时仍出现,更加莫名其妙. 主要原因在于垃圾收集. 还是看代码清楚些.

 

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.OleDb;
using System.IO;

namespace Zrj.Test
...{
    class TestDbCreate
    ...{
        
        static void Main()
        ...{
            Test1();
            
        }
        
        static void Test1()
        ...{
            string file = "testdb.mdb";
            
            File.Delete(file);
            
            CreateDatabase(file);
            Console.WriteLine("Database created.");
            
            OleDbConnection cnn = new OleDbConnection();
            cnn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" + file;
            cnn.Open();
            // do something            
            cnn.Close();
            
            Console.WriteLine("OleDbConnection Closed.");

            int maxTick = 20 * 1000;
            
            int spendTick = DeleteFile(file, maxTick);
            if(spendTick < maxTick)
                Console.WriteLine("Spend {1} ticks to delete {0}", file, spendTick);
            else
                Console.WriteLine("Spend {1} ticks to delete {0}, but not delete", file, spendTick);
        }
        
        
        static int DeleteFile(string file, int maxTick)
        ...{
            int startTick = Environment.TickCount;
            int tryCount = 0;
            
            GC.Collect();        // 关键代码

            do
            ...{
                try
                ...{
                    File.Delete(file);
                }
                catch(IOException)
                ...{
                    ++tryCount;
                    continue;
                }
                
                break;
            }while(Environment.TickCount < (startTick+maxTick));
            
            Console.WriteLine("Total try count is {0}.", ++tryCount);
            return Environment.TickCount - startTick;            
        }
        
        /**////<summary>使用ADOX.Catalog.Create生成Access数据库</summary>
        static void CreateDatabase(string dbFileName)
        ...{
            try
            ...{
                string connectionString1 = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + dbFileName;

                object objCatalog = Activator.CreateInstance(Type.GetTypeFromProgID("ADOX.Catalog"));
                object[] oParams = new object[] ...{ connectionString1 };

                objCatalog.GetType().InvokeMember("Create", System.Reflection.BindingFlags.InvokeMethod, null, objCatalog, oParams);

                System.Runtime.InteropServices.Marshal.ReleaseComObject(objCatalog);
                objCatalog = null;
            }
            catch (Exception ex)
            ...{
                Console.WriteLine("{0} 生成Access数据库出现错误! ", ex.ToString());
            }
        }
    }
}

最后输出:

D:/Temp/test>testdc
Database created.
OleDbConnection Closed.
Total try count is 2.
Spend 31 ticks to delete testdb.mdb