Library: Data
Package: SessionPooling
Header: Poco/Data/SessionPool.h
This class implements session pooling for POCO Data.
Creating a connection to a database is often a time consuming operation. Therefore it makes sense to reuse a session object once it is no longer needed.
A SessionPool manages a collection of SessionImpl objects (decorated with a PooledSessionImpl).
When a SessionImpl object is requested, the SessionPool first looks in its set of already initialized SessionImpl for an available object. If one is found, it is returned to the client and marked as "in-use". If no SessionImpl is available, the SessionPool attempts to create a new one for the client. To avoid excessive creation of SessionImpl objects, a limit can be set on the maximum number of objects. Sessions found not to be connected to the database are purged from the pool whenever one of the following events occurs:
Not connected idle sessions can not exist.
Usage example:
SessionPool pool("ODBC", "...");
...
Session sess(pool.get());
...
Member Functions: allocated, available, capacity, customizeSession, dead, deadImpl, get, idle, onJanitorTimer, purgeDeadSessions, putBack, used
typedef Poco::AutoPtr < PooledSessionHolder > PooledSessionHolderPtr;
typedef Poco::AutoPtr < PooledSessionImpl > PooledSessionImplPtr;
typedef std::list < PooledSessionHolderPtr > SessionList;
SessionPool(
const std::string & sessionKey,
const std::string & connectionString,
int minSessions = 1,
int maxSessions = 32,
int idleTime = 60
);
Creates the SessionPool for sessions with the given sessionKey and connectionString.
The pool allows for at most maxSessions sessions to be created. If a session has been idle for more than idleTime seconds, and more than minSessions sessions are in the pool, the session is automatically destroyed.
If idleTime is 0, automatic cleanup of unused sessions is disabled.
virtual ~SessionPool();
Destroys the SessionPool.
int allocated() const;
Returns the number of allocated sessions.
int available() const;
Returns the number of available (idle + remaining capacity) sessions.
int capacity() const;
Returns the maximum number of sessions the SessionPool will manage.
int dead();
Returns the number of not connected active sessions.
Session get();
Returns a Session.
If there are unused sessions available, one of the unused sessions is recycled. Otherwise, a new session is created.
If the maximum number of sessions for this pool has already been created, a SessionPoolExhaustedException is thrown.
int idle() const;
Returns the number of idle sessions.
int used() const;
Returns the number of sessions currently in use.
virtual void customizeSession(
Session & session
);
Can be overridden by subclass to perform custom initialization of a newly created database session.
The default implementation does nothing.
int deadImpl(
SessionList & rSessions
);
void onJanitorTimer(
Poco::Timer & param55
);
void purgeDeadSessions();
void putBack(
PooledSessionHolderPtr pHolder
);