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/** Definition of the pqxx::notification_receiver functor interface.
*
* pqxx::notification_receiver handles incoming notifications.
*
* DO NOT INCLUDE THIS FILE DIRECTLY; include pqxx/notification instead.
*
* Copyright (c) 2000-2019, Jeroen T. Vermeulen.
*
* See COPYING for copyright license. If you did not receive a file called
* COPYING with this source code, please notify the distributor of this mistake,
* or contact the author.
*/
#ifndef PQXX_H_NOTIFICATION
#define PQXX_H_NOTIFICATION
#include "pqxx/compiler-public.hxx"
#include "pqxx/compiler-internal-pre.hxx"
#include <string>
#include "pqxx/types.hxx"
namespace pqxx
{
/// "Observer" base class for notifications.
/** @addtogroup notification Notifications and Receivers
*
* To listen on a notification issued using the NOTIFY command, derive your own
* class from notification_receiver and define its function-call operator to
* perform whatever action you wish to take when the given notification arrives.
* Then create an object of that class and pass it to your connection. DO NOT
* use raw SQL to listen for notifications, or your attempts to listen won't be
* resumed when a connection fails--and you'll have no way to notice.
*
* Notifications never arrive inside a transaction, not even in a
* nontransaction. Therefore, you are free to open a transaction of your own
* inside your receiver's function invocation operator.
*
* Notifications you are listening for may arrive anywhere within libpqxx code,
* but be aware that @b PostgreSQL @b defers @b notifications @b occurring
* @b inside @b transactions. (This was done for excellent reasons; just think
* about what happens if the transaction where you happen to handle an incoming
* notification is later rolled back for other reasons). So if you're keeping a
* transaction open, don't expect any of your receivers on the same connection
* to be notified.
*
* (For very similar reasons, outgoing notifications are also not sent until the
* transaction that sends them commits.)
*
* Multiple receivers on the same connection may listen on a notification of the
* same name. An incoming notification is processed by invoking all receivers
* (zero or more) of the same name.
*/
class PQXX_LIBEXPORT PQXX_NOVTABLE notification_receiver
{
public:
/// Register the receiver with a connection.
/**
* @param c Connnection to operate on.
* @param channel Name of the notification to listen for.
*/
notification_receiver(connection_base &c, const std::string &channel);
notification_receiver(const notification_receiver &) =delete;
notification_receiver &operator=(const notification_receiver &) =delete;
virtual ~notification_receiver();
/// The channel that this receiver listens on.
const std::string &channel() const { return m_channel; }
/// Overridable: action to invoke when notification arrives.
/**
* @param payload On PostgreSQL 9.0 or later, an optional string that may have
* been passed to the NOTIFY command.
* @param backend_pid Process ID of the database backend process that served
* our connection when the notification arrived. The actual process ID behind
* the connection may have changed by the time this method is called.
*/
virtual void operator()(const std::string &payload, int backend_pid) =0;
protected:
connection_base &conn() const noexcept { return m_conn; }
private:
connection_base &m_conn;
std::string m_channel;
};
}
#include "pqxx/compiler-internal-post.hxx"
#endif
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