Charlie’s path to dEAth

结论

• SQL Server CLR是一个多线程运行的环境。
• 静态变量等线程安全问题，在CLR环境中存在。

摘录《Professional SQL Server™ 2005 CLR Programming》

SQL Server 2005 hosts the CLR in a “sandbox”-like environment in-process to itself, as you can see Figure 1-2. When a user requests a SQL CLR object for the first time, SQL Server will load the .NET execution engine mscoree.dll (which is the CLR) into memory. 

实验

CLR代码

public partial class ProcessThread
{
    public static int static_i=0;

    [Microsoft.SqlServer.Server.SqlFunction(IsDeterministic = true, IsPrecise = true)]
    public static SqlString PID()
    {
        return  Process.GetCurrentProcess().Id.ToString();
    }

    [Microsoft.SqlServer.Server.SqlFunction(IsDeterministic = true, IsPrecise = true)]
    public static SqlString TID()
    {
        return AppDomain.GetCurrentThreadId().ToString()+ ":"+
            System.Threading.Thread.CurrentThread.ManagedThreadId.ToString();
    }

    [Microsoft.SqlServer.Server.SqlFunction(IsDeterministic = true, IsPrecise = true)]
    public static SqlString StaticI()
    {
        return (static_i++).ToString();
    }

};

安装CLR的SQL代码

CREATE ASSEMBLY sqlclr_test
FROM 'C:\SQLCLR\bin\Release\sqlclr.dll'
WITH permission_set = UNSAFE;
GO

create function fn_processid () returns nvarchar(max)
as external name sqlclr_test.ProcessThread.PID
GO
create function fn_threadid () returns nvarchar(max)
as external name sqlclr_test.ProcessThread.TID
GO
create function fn_statici () returns nvarchar(max)
as external name sqlclr_test.ProcessThread.StaticI
GO

测试用查询命令

select
    dbo.fn_processid() as [ProcessID],
    dbo.fn_threadid()  as [ThreadID],
    dbo.fn_statici()   as [StaticI]

返回结果

系统进程截图 (Process Explorer) 

现象 

1. 每次执行查询命令，得到的ThreadID会发生变化，在SQL Server的进程包含的线程池中轮转。
2. 每次执行查询命令，不论是否同一个线程，StaticI的值会增加。
3. SQL Server的用户进程（登录），与所执行的线程编号几乎没有关系。

Filed by charlie at 6:47 am under Coding, DBA