ZeroTierOne/ext/libpqxx-7.7.3/include/pqxx/notification.hxx

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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) 2000-2022, 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
#if !defined(PQXX_HEADER_PRE)
# error "Include libpqxx headers as <pqxx/header>, not <pqxx/header.hxx>."
#endif
#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 **PostgreSQL defers notifications occurring inside
* 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 &c, std::string_view channel);
/// Register the receiver with a connection.
notification_receiver(notification_receiver const &) = delete;
/// Register the receiver with a connection.
notification_receiver &operator=(notification_receiver const &) = delete;
/// Deregister the receiver.
virtual ~notification_receiver();
/// The channel that this receiver listens on.
[[nodiscard]] std::string const &channel() const & { return m_channel; }
// TODO: Change API to take payload as zview instead of string ref.
/// Overridable: action to invoke when notification arrives.
/**
* @param payload 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()(std::string const &payload, int backend_pid) = 0;
protected:
connection &conn() const noexcept { return m_conn; }
private:
connection &m_conn;
std::string m_channel;
};
} // namespace pqxx
#endif