/// <summary>
/// This returns a connection from the cache, or creates a new one if necessary.
///
/// This method is thread safe.
///
/// This method improved one test's performance (the only one I measured) by about 20%.
///
/// Since some databases cannot have more than one connection at a time, we ask the
/// connection descriptor whether we can actually cache the connection or not.
/// </summary>
public IDbConnection Get(AbstractSqlConnectionDescriptor connDesc)
{
IDbConnection conn = null;
if (connDesc.UsePooling())
{
// If it is a pooled connection, check if we have one in our cache.
lock (_cache)
{
if (_cache.ContainsKey(connDesc))
{
TimestampedData<IDbConnection> connFromCache = _cache[connDesc];
// This pool only caches one connection for a connection string.
_cache.Remove(connDesc);
// Don't reuse a connection that was cached more than 5 minutes ago. We use
// this cache to handle the case of thousands per second, if we're querying
// every 5 minutes we can take the time to create a new connection.
if (connFromCache.Time.Ticks < (DateTime.Now.Ticks - 3000000000))
{
try
{
connFromCache.Data.Close();
}
catch (Exception e)
{
_log.Debug("Exception while closing a connection that was probably expired anyway: " +
connDesc, e);
}
}
else
{
conn = connFromCache.Data;
}
}
}
}
// If it's a bad/broken/something connection, we want a new one also.
if ((conn == null) || (conn.State != ConnectionState.Open))
{
// Make a new one and put it in the cache.
conn = connDesc.CreateNewConnection();
try
{
conn.Open();
if (_log.IsDebugEnabled)
{
_log.Debug("Opened connection to: " + connDesc);
}
lock (_errorCount)
{
_errorCount[connDesc] = 0;
}
}
catch (Exception e)
{
// Increment the number of consecutive failures.
int newCount = 1;
lock (_errorCount)
{
if (_errorCount.ContainsKey(connDesc))
{
newCount = _errorCount[connDesc] + 1;
}
_errorCount[connDesc] = newCount;
}
throw new UnableToConnectException(connDesc, newCount, e);
}
}
return conn;
}
/// <summary>
/// Inserts the connection into the cache IF we don't have one already (we only cache one
/// connection per unique descriptor).
///
/// This method is thread safe.
///
/// Due to MS Access not allowing more than one connection to have the DB locked for modifying at
/// one time, any connections to Access DBs are closed and not cached.
/// </summary>
public void Return(AbstractSqlConnectionDescriptor connDesc, IDbConnection conn)
{
bool closeConn = false;
if (!connDesc.UsePooling())
{
closeConn = true;
}
else
{
lock (_cache)
{
if (_cache.ContainsKey(connDesc))
{
// already have a connection for this connstr. We're tolerant of this, just
// go ahead and close the second connection.
closeConn = true;
}
else
{
_cache[connDesc] = new TimestampedData<IDbConnection>(conn);
}
}
}
if (closeConn)
{
// Not caching it, just close it.
try
{
if (_log.IsDebugEnabled)
{
_log.Debug("Closing DB connection: " + conn.ConnectionString);
}
conn.Close();
}
catch (Exception e)
{
// This exception is not rethrown because we don't want to mask any
// previous exception that might be being thrown out of "invokeMe".
_log.Warn("Caught an exception while trying to close a DB connection we just used.", e);
}
}
}
