I was using this code:
public class SQLConnection : IConnection
{
private SqlConnection _sqlConnection = null;
//bunch of interface implementations for my project
//the destructor
~SQLConnection()
{
if(_sqlConnection != null)
{
if(_sqlConnection.State == ConnectionState.Open)
{
_sqlConnection.Close();
}
_sqlConnection.Dispose();
}
}
}
This was working well until some time ago, when I started receiving this error: Internal .Net Framework Data Provider error 1
After googling a bit, I found this link (the Caution part) and I think that's what's happening to me.
My class was managing the connection state opening and closing each time, but now that it seems I can't manage it this way, is there any other way that I can do this without having to go to every function that I use the connection and call connection.Close() explicitly?
Always use 'using' for safely disposing the connections.
using(var _sqlConnection = new SqlConnection())
{
//code here
_sqlConnection.Open();
}
//Safely disposed.
Also, it is never a good idea to use destructor explicitly in C# code unless you have unmanaged code.
You're probably receiving this error when one code is trying to access SQLConnection that has been already garbage collected. This usually will happen in cases like this one
SqlConnection sqlConn;
using (var sqlConnection = new SqlConnection())
{
sqlConn = sqlConnection;
sqlConnection.Open();
}
sqlConn.Close();
I know this example looks silly as it's overly simplified, but it happens often when programmers tend to share a connection object between Managing Classes. Look for any recent changes in your code. Maybe you're passing an instance of a connection between multiple objects. One of those objects gets Garbage Collected and in turn the connection gets disposed too.
Related
I am working on a project which, up until today, has been fine. However now when I run it and it goes through a few different Stored Procedure calls it is throwing an InvalidOperationException with the message The connection was not closed. The connection's current state is open.
I get that I could put in a check to see if the connection is already open, but this code hasn't changed (it is under Version Control and isn't modified) so I'm looking for other potential explanations.
Could there be some lock in SQL which isn't being released? Is there a process which I should look out for and kill?
I can't really post the code as there is a lot of it, and it is split up into smaller methods which makes it harder to pull out individual items. E.g:
public SqlConnection Connection
{
get
{
this._connection.Open();
return _connection;
}
}
public IDataReader RetrieveRecord(int Id)
{
//SP
SqlCommand cmd = this.Connection.CreateCommand();
cmd.CommandText = "SelectRecord";
cmd.CommandType = CommandType.StoredProcedure;
//Parameters
cmd.Parameters.Add(new SqlParameter("#tID", Id));
//instruct the data reader to close its connection when its Close method is called by passing the CommandBehavior.CloseConnection
return cmd.ExecuteReader(CommandBehavior.CloseConnection);
}
Nothing massively complex, I just don't understand why this connection is now throwing an exception.
The DAL is not stable enough:
You open a Connection that is not closed if something goes wrong in RetrieveRecord.
You should create a new connection inside RetrieveRecord and close it there in a finally block.
Opening a connection is cheap thanks to Connection Pooling.
Problem is with the line
this._connection.Open();
Because you are trying to open an already opened connection.
Try this to check before opening a connection:
if (this._connection.State == ConnectionState.Closed)
this._connection.Open();
Sorted. Two reboots cleared whatever was keeping the connection open.
When you are talking about killing process, I think you know c# well.
You should always use
using()
{
}
Like:
using(SqlConnection con=new SqlConnection("connectionString"))
{
// Do something with con
using(SqlCommand cmd=new SqlCommand("cmdText",con))
{
// Do something with cmd
}
}
You know that SqlCommand and SqlConnection implement IDisposable
So when you put those objects within using, the connection closing and clean up job is automatically done.
No need to close the connection manually in the code, since using will do the work for you.
I am designing a database wrapper for C#.
Below are the two options I have:
Option A:
class DBWrapper:IDisposable
{
private SqlConnection sqlConn;
public DBWrapper()
{
sqlConn = new SqlConnection("my connection string");
sqlConn.Open();
}
public DataTable RunQuery(string Sql)
{
implementation......
}
public Dispose()
{
if(sqlConn != null)
sqlConn.Close();
}
}
Option B:
class DBWrapper
{
public DBWrapper()
{
}
public DataTable RunQuery(string Sql)
{
SqlConnection sqlConn = new SqlConnection("my connection string");
.....implementation......
sqlConn.Close();
}
}
For option A connection is opened when class is instantiated. So no matter how many times the caller calls RunQuery the connection is always ready. But If the application instantiates DBWrapper early in the application, the connection will be just opened and doing nothing until the application is finished. Also, it could have many DBWrapper instantiated during the execution. So, it's kinda wasting resources.
For option B it doesn't have the problem option A has, but the a new connection has to be opened and closed everytime the caller calls RunQuery. I am not sure how much it will hurt the performance.
Please share your expertise. Thank you for reading.
For performance reasons, you'll definitely not want to go with Option B (at least in the cases I experienced.)
Let me suggest Option C:
class DBWrapper:IDisposable {
private SqlConnection sqlConn;
public void EnsureConnectionIsOpen()
{
if (sqlConn == null)
{
sqlConn = new SqlConnection("my connection string");
sqlConn.Open();
}
}
public DataTable RunQuery(string Sql)
{
EnsureConnectionIsOpen();
implementation......
}
public Dispose()
{
if(sqlConn != null)
sqlConn.Close();
}
}
You might consider using the singleton pattern to make sure there is only one instance of your DBWrapper.
A few comments worth considering:
In the approach where you manage a (perhaps) long-lived connection, it is important to check whether the connection is open before running a query. I've run into issues before where NETCF closed unused connections after a while.
In the approach where you open a new connection per-query, ensure that your connection, commands, and (if used) data readers are all properly wrapped in using statements or try/finally+dispose() blocks to free up connections and locks.
Happy coding!
Garbage collector is triggered under rather complex conditions but basically it is invoked when memory exceeds some limit, it is invoked periodically as well but the period is not constant. You never can be sure when exactly garbage collector disposes and consequently (in another run) destroys the object. One thing you can be sure is the fact that garbage collector will never dispose and destroy the object that still has references. For example object that is referenced via static variables on the class neither will be disposed nor destroyed.
Option B is more transactional, which has its advantages. ADO.NET uses implicit connection pooling, so you do not have to worry about creating new instances of SqlConnection frequently.
You should consider whether you are using a connected or disconnected data model; as the second approach lends itself better to a disconnected model.
But as i've said above, connection pooling means that it makes virtually no difference in practical terms.
You could have an option C where the database is opened on request in RunQuery (if it is not open) and closed on disposed (when it was opened). That way the database is only opened when really needed and will be opened only once.
So in pseudo code:
class DBWrapper
{
public DBWrapper()
{
}
SqlConnection sqlConn = null;
public DataTable RunQuery(string Sql)
{
if(sqlConn == null) sqlConn = new SqlConnection("my connection string");
.....implementation......
}
public Dispose()
{
if(sqlConn != null)
sqlConn.Close();
}
}
Also mind that the moment Dispose is called is not always directly after the object is not needed anymore (for example a function variable after the function is used). As far as I know it will be executed when the garbage collector collects the object (which is not directly). But I am not totally sure about this. This behaviour might also differ between web and non web application.
I have the code below to query records from a stored procedure but am concerned I may not be disposing what I need to or am disposing when the object would be cleared by the Garbage Collector shortly afterward anyway.
Do I need to dispose the SqlDataReader since it is within the try catch block?
Do I need to run both cmd.Dispose and cmd.Connection.Close or does one infer the other?
Would the garbage collector eventually dispose of all these objects anyway (maybe not timely enough) or do these objects implictly require dispose possibly because of using unmanaged code?
public void GetData(string studentID)
{
SqlCommand cmd = new SqlCommand("sp_stored_proc",
new SqlConnection(Settings.Default.connectionString))
{ CommandType = CommandType.StoredProcedure };
try
{
cmd.Connection.Open();
cmd.Parameters.AddWithValue("#student_id", studentID);
SqlDataReader dr = cmd.ExecuteReader();
//do something with the data
if (dr != null)
dr.Dispose();
}
catch
{
//error handling
}
finally
{
if (cmd != null)
{
cmd.Dispose();
cmd.Connection.Close();
}
}
}
You should dispose the data reader, and the command. No need to separately close the connection if you dispose the command. You should ideally do both using a using block:
using (SqlCommand cmd = new...)
{
// do stuff
using (SqlDataReader dr = cmd.ExecuteReader())
{
// do stuff
}
}
If you need exception handling do that separately either inside or around the using blocks - no need for the finally for the Dispose calls though with using.
If you use something like this:
public void GetData(string studentID)
{
using (SqlConnection connection = new SqlConnection(Settings.Default.connectionString))
{
connection.Open();
using (SqlCommand command = connection.CreateCommand())
{
command.CommandType = CommandType.StoredProcedure;
command.CommandText = "sp_stored_proc";
command.Parameters.AddWithValue("#student_id", studentID);
using (SqlDataReader dataReader = command.ExecuteReader())
{
// do something with the data
}
}
}
}
then all of your Disposable objects will get disposed of correctly. Calling Dispose() on the SqlConnection, SqlCommand and SqlDataReader objects (which is what the using block does when it exits) closes them correctly.
Additionally, this approach keeps all of your variables scoped to where they are used.
The downside to this approach is that if you need error handling using a try/catch, you have to either wrap it around the whole method body, or use several of them to handle connection errors differently from reading errors, etc...
Do I need to dispose the SqlDataReader
since it is within the try catch
block?
-- Yes, as being inside of the try catch will not call the dispose method.
Do I need to run both cmd.Dispose and cmd.Connection.Close or does one infer the other?
-- Yes, you need to run both. Calling Cmd.dispose does not close the connection.
The dispose method is meant to be used by the programmer to clean up resources which either aren't directly managed by the garbage collector, or the need to be cleared out after the program is done using them to free up space. Technically, one could set up the program so the GC would handle it's disposal, but that's an assumption I wouldn't make, especially since the programmer writing the class exposed the dispose method for you. Putting the Command in a using statement is probably the easiest route, because you know it will get disposed when the code leaves the declaration space.
using (var connection = new Connection ())
{
using (var cmd = new Command())
{
}
}
Personally if something has a dispose method then it is worth using it anyway as they will prevent protential memory leaks.
To make a long story short; if it implements IDisposable, you should call Dispose.
Even if you use Reflector to figure out that Dispose in one object invokes Dispose on another object, I would still recommend to call Dispose on both, since this is internal implementation details that may change in some future release, so you should not rely on that always being true.
So, Dispose anything that is IDisposable.
you should open Connection firstly by Connection.Open();
then use the methods such as SqlDataReader to read
after all,close SqlDataReader firstly and then close connection
you can use keyword "using" to dispose it, but it is not a good idea
in fact the keyword "using" is to dispose the object automatically.
in other word,the object should achieve dispose method
Please help!
Background info
I have a WPF application which accesses a SQL Server 2005 database. The database is running locally on the machine the application is running on.
Everywhere I use the Linq DataContext I use a using { } statement, and pass in a result of a function which returns a SqlConnection object which has been opened and had an SqlCommand executed using it before returning to the DataContext constructor.. I.e.
// In the application code
using (DataContext db = new DataContext(GetConnection()))
{
... Code
}
where getConnection looks like this (I've stripped out the 'fluff' from the function to make it more readable, but there is no additional functionality that is missing).
// Function which gets an opened connection which is given back to the DataContext constructor
public static System.Data.SqlClient.SqlConnection GetConnection()
{
System.Data.SqlClient.SqlConnection Conn = new System.Data.SqlClient.SqlConnection(/* The connection string */);
if ( Conn != null )
{
try
{
Conn.Open();
}
catch (System.Data.SqlClient.SqlException SDSCSEx)
{
/* Error Handling */
}
using (System.Data.SqlClient.SqlCommand SetCmd = new System.Data.SqlClient.SqlCommand())
{
SetCmd.Connection = Conn;
SetCmd.CommandType = System.Data.CommandType.Text;
string CurrentUserID = System.String.Empty;
SetCmd.CommandText = "DECLARE #B VARBINARY(36); SET #B = CAST('" + CurrentUserID + "' AS VARBINARY(36)); SET CONTEXT_INFO #B";
try
{
SetCmd.ExecuteNonQuery();
}
catch (System.Exception)
{
/* Error Handling */
}
}
return Conn;
}
I do not think that the application being a WPF one has any bearing on the issue I am having.
The issue I am having
Despite the SqlConnection being disposed along with the DataContext in Sql Server Management studio I can still see loads of open connections with :
status : 'Sleeping'
command : 'AWAITING COMMAND'
last SQL Transact Command Batch : DECLARE #B VARBINARY(36); SET #B = CAST('GUID' AS VARBINARY(36)); SET CONTEXT_INFO #B
Eventually the connection pool gets used up and the application can't continue.
So I can only conclude that somehow running the SQLCommand to set the Context_Info is meaning that the connection doesn't get disposed of when the DataContext gets disposed.
Can anyone spot anything obvious that would be stopping the connections from being closed and disposed of when the DataContext they are used by are disposed?
From MSDN (DataContext Constructor (IDbConnection)):
If you provide an open connection, the
DataContext will not close it.
Therefore, do not instantiate a
DataContext with an open connection
unless you have a good reason to do
this.
So basically, it looks like your connections are waiting for GC to finalize them before they will be released. If you have lots of code that does this, one approach might be to overide Dispose() in the data-context's partial class, and close the connection - just be sure to document that the data-context assumes ownership of the connection!
protected override void Dispose(bool disposing)
{
if(disposing && this.Connection != null && this.Connection.State == ConnectionState.Open)
{
this.Connection.Close();
this.Connection.Dispose();
}
base.Dispose(disposing);
}
Personally, I would happily give it (regular data-context, w/o the hack above) an open connection as long as I was "using" the connection (allowing me to perform multiple operations) - i.e.
using(var conn = GetConnection())
{
// snip: some stuff involving conn
using(var ctx = new FooContext(conn))
{
// snip: some stuff involving ctx
}
// snip: some more stuff involving conn
}
The SqlProvider used by the LINQ DataContext only closes the SQL connection (through SqlConnectionManager.DisposeConnection) if it was the one to open it. If you give an already-open SqlConnection object to the DataContext constructor, it will not close it for you. Thus, you should write:
using (SqlConnection conn = GetConnection())
using (DataContext db = new DataContext(conn))
{
... Code
}
I experienced the same issue using the Entity Framework. My ObjectContext was wrapped around a using block.
A connection was established when I called SaveChanges(), but after the using statement was out of scope, I noticed that SQL Management Studio still had a "AWAITING COMMAND" for the .NET SQL Client.
It looks like this has to do with the behavior of the ADO.NET provider which has connection pooling turned on by default.
From "Using Connection Pooling with SQL Server" on MSDN (emphasis mine):
Connection pooling reduces the number of times that new connections need to be opened. The pooler maintains ownership of the physical connection. It manages connections by keeping alive a set of active connections for each given connection configuration. Whenever a user calls Open on a connection, the pooler looks to see if there is an available connection in the pool. If a pooled connection is available, it returns it to the caller instead of opening a new connection. When the application calls Close on the connection, the pooler returns it to the pooled set of active connections instead of actually closing it. Once the connection is returned to the pool, it is ready to be reused on the next Open call.
Also ClearAllPools and ClearPool seems useful to explicitly close all pooled connections if needed.
I think the connection, while no longer referenced, is waiting for the GC to dispose of it fully.
Solution:
Create your own DataContext class which derives from the auto-generated one. (rename the base one so you don't have to change any other code).
In your derived DataContext - add a Dispose() function. In that - dispose the inner connection.
Well thanks for the help chaps, it has been solved now..
Essentially I took elements of most of the answers above and implemented the DataContext constructor as above (I already had overloaded the constructors so it wasn't a big change).
// Variable for storing the connection passed to the constructor
private System.Data.SqlClient.SqlConnection _Connection;
public DataContext(System.Data.SqlClient.SqlConnection Connection) : base(Connection)
{
// Only set the reference if the connection is Valid and Open during construction
if (Connection != null)
{
if (Connection.State == System.Data.ConnectionState.Open)
{
_Connection = Connection;
}
}
}
protected override void Dispose(bool disposing)
{
// Only try closing the connection if it was opened during construction
if (_Connection!= null)
{
_Connection.Close();
_Connection.Dispose();
}
base.Dispose(disposing);
}
The reason for doing this rather than some of the suggestions above is that accessing this.Connection in the dispose method throws a ObjectDisposedException.
And the above works as well as I was hoping!
The Dispose should close the connections, as MSDN points out:
If the SqlConnection goes out of
scope, it won't be closed. Therefore,
you must explicitly close the
connection by calling Close or
Dispose. Close and Dispose are
functionally equivalent. If the
connection pooling value Pooling is
set to true or yes, the underlying
connection is returned back to the
connection pool. On the other hand, if
Pooling is set to false or no, the
underlying connection to the server is
closed.
My guess would be that your problem has something to do with GetContext().
I use a pattern that looks something like this often. I'm wondering if this is alright or if there is a best practice that I am not applying here.
Specifically I'm wondering; in the case that an exception is thrown is the code that I have in the finally block enough to ensure that the connection is closed appropriately?
public class SomeDataClass : IDisposable
{
private SqlConnection _conn;
//constructors and methods
private DoSomethingWithTheSqlConnection()
{
//some code excluded for brevity
try
{
using (SqlCommand cmd = new SqlCommand(SqlQuery.CountSomething, _SqlConnection))
{
_SqlConnection.Open();
countOfSomething = Convert.ToInt32(cmd.ExecuteScalar());
}
}
finally
{
//is this the best way?
if (_SqlConnection.State == ConnectionState.Closed)
_SqlConnection.Close();
}
//some code excluded for brevity
}
public Dispose()
{
_conn.Dispose();
}
}
Wrap your database handling code inside a "using"
using (SqlConnection conn = new SqlConnection (...))
{
// Whatever happens in here, the connection is
// disposed of (closed) at the end.
}
The .Net Framework mantains a connection pool for a reason. Trust it! :)
You don't have to write so much code just to connect to the database and release the connection.
You can just use the 'using' statement and rest assured that 'IDBConnection.Release()' will close the connection for you.
Highly elaborate 'solutions' tend to result in buggy code. Simple is better.
MSDN Docs make this pretty clear...
The Close method rolls back any pending transactions. It then releases the connection to the connection pool, or closes the connection if connection pooling is disabled.
You probably haven't (and don't want to) disable connection pooling, so the pool ultimately manages the state of the connection after you call "Close". This could be important as you may be confused looking from the database server side at all the open connections.
An application can call Close more than one time. No exception is generated.
So why bother testing for Closed? Just call Close().
Close and Dispose are functionally equivalent.
This is why a using block results in a closed connection. using calls Dispose for you.
Do not call Close or Dispose on a Connection, a DataReader, or any other managed object in the Finalize method of your class.
Important safety tip. Thanks, Egon.
I'm guessing that by _SqlConnection.State == ConnectionState.Closed you meant !=
This will certainly work. I think it is more customary to contain the connection object itself inside a using statement, but what you have is good if you want to reuse the same connection object for some reason.
One thing that you should definitely change, though, is the Dispose() method. You should not reference the connection object in dispose, because it may have already been finalized at that point. You should follow the recommended Dispose pattern instead.
Since you're using IDisposables anyway. You can use the 'using' keyword, which is basically equivalent to calling dispose in a finally block, but it looks better.
See this question for the answer:
Close and Dispose - which to call?
If your connection lifetime is a single method call, use the using feature of the language to ensure the proper clean-up of the connection. While a try/finally block is functionally the same, it requires more code and IMO is less readable. There is no need to check the state of the connection, you can call Dispose regardless and it will handle cleaning-up the connection.
If your connection lifetime corresponds to the lifetime of a containing class, then implement IDisposable and clean-up the connection in Dispose.
Put the connection close code inside a "Finally" block like you show. Finally blocks are executed before the exception is thrown. Using a "using" block works just as well, but I find the explicit "Finally" method more clear.
Using statements are old hat to many developers, but younger developers might not know that off hand.
no need for a try..finally around a "using", the using IS a try..finally
Might I suggest this:
class SqlOpener : IDisposable
{
SqlConnection _connection;
public SqlOpener(SqlConnection connection)
{
_connection = connection;
_connection.Open();
}
void IDisposable.Dispose()
{
_connection.Close();
}
}
public class SomeDataClass : IDisposable
{
private SqlConnection _conn;
//constructors and methods
private void DoSomethingWithTheSqlConnection()
{
//some code excluded for brevity
using (SqlCommand cmd = new SqlCommand("some sql query", _conn))
using(new SqlOpener(_conn))
{
int countOfSomething = Convert.ToInt32(cmd.ExecuteScalar());
}
//some code excluded for brevity
}
public void Dispose()
{
_conn.Dispose();
}
}
Hope that helps :)