一起谈.NET技术,详解ADO.NET连接池

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一起谈.NET技术,详解ADO.NET连接池

狼人2007 浏览449
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ADO.NET中提供了连接池的功能,多数开发人员很少设置它,因为它是默认的。

界面设置如下图:

 

关闭连接池也很简单,在连接字符串如下:

Data Source=(local);Initial Catalog=AdventureWorks;Integrated Security=SSPI;Pooling=False;

但连接池的本质是什么样的呢?

 

Reflector,打开System.Data.SqlClient.SqlConnectionConnectionString属性的设置值的方法,如下:

 

代码

private void ConnectionString_Set(string value)
{
DbConnectionOptions userConnectionOptions
= null;
DbConnectionPoolGroup group
= this.ConnectionFactory.GetConnectionPoolGroup(value, null,
 
ref userConnectionOptions);
DbConnectionInternal innerConnection
= this.InnerConnection;
bool allowSetConnectionString = innerConnection.AllowSetConnectionString;
if (allowSetConnectionString)
{
allowSetConnectionString
= this.SetInnerConnectionFrom(DbConnectionClosedBusy.
SingletonInstance, innerConnection);
if (allowSetConnectionString)
{
this._userConnectionOptions = userConnectionOptions;
this._poolGroup = group;
this._innerConnection = DbConnectionClosedNeverOpened.SingletonInstance;
}
}
if (!allowSetConnectionString)
{
throw ADP.OpenConnectionPropertySet("ConnectionString", innerConnection.State);
}
if (Bid.TraceOn)
{
string str = (userConnectionOptions != null) ? userConnectionOptions.
UsersConnectionStringForTrace() :
"";
Bid.Trace(
" %d#, '%ls'\n", this.ObjectID, str);
}

}

 

 

 

再连接 到红色的GetConnectionPoolGroup方法,如下代码

 


internal DbConnectionPoolGroup GetConnectionPoolGroup(string connectionString,
DbConnectionPoolGroupOptions poolOptions,
ref DbConnectionOptions userConnectionOptions)
{

DbConnectionPoolGroup group;

if (ADP.IsEmpty(connectionString))

{

return null;

}

if (!this._connectionPoolGroups.TryGetValue(connectionString, out group) ||
(group.IsDisabled
&& (group.PoolGroupOptions != null)))

{

DbConnectionOptions options
= this.CreateConnectionOptions(connectionString,
userConnectionOptions);

if (options == null)

{

throw ADP.InternalConnectionError(ADP.ConnectionError.ConnectionOptionsMissing);

}

string str = connectionString;

if (userConnectionOptions == null)

{

userConnectionOptions
= options;

str
= options.Expand();

if (str != connectionString)

{

return this.GetConnectionPoolGroup(str, null, ref userConnectionOptions);

}

}

if ((poolOptions == null) && ADP.IsWindowsNT)

{

if (group != null)

{

poolOptions
= group.PoolGroupOptions;

}

else

{

poolOptions
= this.CreateConnectionPoolGroupOptions(options);

}

}

DbConnectionPoolGroup group2
= new DbConnectionPoolGroup(options, poolOptions) {

ProviderInfo
= this.CreateConnectionPoolGroupProviderInfo(options)

};

lock (this)

{

Dictionary dictionary
= this._connectionPoolGroups;

if (!dictionary.TryGetValue(str, out group))

{

Dictionary dictionary2
= new Dictionary(1 + dictionary.Count);

foreach (KeyValuePair pair in dictionary)

{

dictionary2.Add(pair.Key, pair.Value);

}

dictionary2.Add(str, group2);

this.PerformanceCounters.NumberOfActiveConnectionPoolGroups.Increment();

group
= group2;

this._connectionPoolGroups = dictionary2;

}

return group;

}

}

if (userConnectionOptions == null)

{

userConnectionOptions
= group.ConnectionOptions;

}

return group;

}

 

 

 

TryGetValue是判断是否存在连接字符串为connectionString的连接,存在返回到group,不存在就调用CreateConnectionOptions创建一个DbConnectionOptions,最后用

 


lock (this)
{

Dictionary dictionary
= this._connectionPoolGroups;

if (!dictionary.TryGetValue(str, out group))

{

Dictionary dictionary2
= new Dictionary(1 + dictionary.Count);

foreach (KeyValuePair pair in dictionary)

{

dictionary2.Add(pair.Key, pair.Value);

}

dictionary2.Add(str, group2);

this.PerformanceCounters.NumberOfActiveConnectionPoolGroups.Increment();

group
= group2;

this._connectionPoolGroups = dictionary2;

}

return group;

}

 

 

 

这段代码放到连接池中,在这里,可能显示的看到,ado.NET的连接池实质上是一个Dictionary泛型集合。

所谓的连接池,就是一个与连接对象Connection相关的集合,这不只是简单的集合,而是有一定的机制在内部。我们做开发时,可能建立Connection连接对象,关闭连接对象,有时候还调用Dispose来释放连接。下次再用时,便重新实例化一个连接。但在池中的连接不随连接对象的CloseDispose而释放。如果下次重新建立连接,连接字符串与前一次完全一模一样,则连接池就会把上次可用的连接对象赋给连接去用。如果两个连接字符串有一点不一样,即使在某一个地方多一个空格,连接池也不会以为是相同的连接,这点微软可能在内部只直接去比较两个字符串了,而不是比较连接数据库字符串的键值互相匹配。

连接池的好处就是保留连接对象,防止下次重头再来实例化一个连接对象。


string constr1 = "Data Source=(local);Initial Catalog=AdventureWorks;Integrated
Security=SSPI;
";
string constr2 = "Data Source=(local);Initial Catalog=Pubs;Integrated Security=SSPI;";
string AssMark = "System.Data,Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561
934e089
";
Assembly ass
= Assembly.Load(AssMark);

Type SqlConType
= null;

foreach (Type conType in ass.GetExportedTypes())
{

Console.WriteLine(conType .ToString ());

if ("System.Data.SqlClient.SqlConnection" == conType.ToString())
{
SqlConType
= conType;

}

}

if (SqlConType != null)

{

Type[] types1
= new Type[0];

ConstructorInfo constructorInfoObj1
= SqlConType.GetConstructor(

BindingFlags.Instance
| BindingFlags.Public, null,

CallingConventions.HasThis, types1,
null);

SqlConnection con1
= (SqlConnection)constructorInfoObj1.Invoke(null);

con1.ConnectionString
= constr1;

SqlConnection con2
= (SqlConnection)constructorInfoObj1.Invoke(null);

con2.ConnectionString
= constr2;

PropertyInfo PI
= SqlConType.GetProperty("PoolGroup", BindingFlags.Instance |
BindingFlags.NonPublic);

object poolGroup1 = PI.GetValue(con1, null);

object poolGroup2 = PI.GetValue(con2, null);

}

 

说明:可能找到结果后觉得非常简单,但怎么找到结果的,却是费了很大劲,几乎是5个小时,所以相把找到结果的过程简单说一下:

一开始用Reflector发现SqlConnection中有一个PoolGroup的属性,于是就想在运行时候比较两个SqlConnection对象的这个属性,但由于这个属性是的访问修饰符是internal的,不能直接访问,只有用反射,代码(是经过优化的)如下:

然后在倒数第一行设置断点,为比较poolGroup1poolGroup2的不同,结果发现,当连接字符串一样时,这两个对象的_objectID相同,字符串有一点不同就会不同,这点说明连接池中是用字符串本身比较的,而不是字符串中键值对进行比较。同还发现当con1con2ConnectionString不赋值时这两个对象都是null,由此说明关键是ConnectionString赋值上,所以才开始用Reflector查看这个属性的赋值方法,才有上面的代码。)

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