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/*
* Copyright (c) 2008-2019, Hazelcast, Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hazelcast.cp.session;
import com.hazelcast.config.cp.CPSubsystemConfig;
import com.hazelcast.nio.Address;
/**
* Represents a CP session.
*
* For CP data structures that are doing ownership management of the resources,
* such as lock or semaphore, a session is required to keep track of the
* liveliness of the caller. In this context, caller means an entity that
* uses the CPI subsystem APIs. It can be either a Hazelcast server or client.
* A caller initially creates a session before sending its very first
* session-based request to the CP group, such as a lock / semaphore acquire.
* After creating a session on the CP group, the caller stores its session id
* locally and sends it alongside its session-based operations. A single
* session is used for all lock and semaphore proxies of the caller. When a CP
* group receives a session-based operation, it checks the validity of the
* session using the session id information available in the operation.
* A session is valid if it is still open in the CP group. An operation with
* a valid session id is accepted as a new session heartbeat. While a caller is
* idle, in other words, it does not send any session-based operation to the CP
* group for a while, it commits periodic heartbeats to the CP group
* in the background in order to keep its session alive. This interval is
* specified in {@link CPSubsystemConfig#getSessionHeartbeatIntervalSeconds()}.
*
* A session is closed when the caller does not touch the session during
* a predefined duration. In this case, the caller is assumed to be crashed and
* all its resources are released automatically. This duration is specified in
* {@link CPSubsystemConfig#getSessionTimeToLiveSeconds()}. Please check
* {@link CPSubsystemConfig} to learn the recommendations for choosing
* a reasonable session time-to-live duration.
*
* Sessions offer a trade-off between liveliness and safety. If a very small
* value is set to {@link CPSubsystemConfig#setSessionTimeToLiveSeconds(int)},
* then a session owner could be considered crashed very quickly and its
* resources can be released prematurely. On the other hand, if a large value
* is set, a session could be kept alive for an unnecessarily long duration
* even if its owner actually crashes.
*
* @see CPSubsystemConfig
*/
public interface CPSession {
/**
* Represents type of endpoints that create CP sessions
*/
enum CPSessionOwnerType {
/**
* Represents a Hazelcast server
*/
SERVER,
/**
* Represents a Hazelcast client
*/
CLIENT
}
/**
* Returns id of the session
*/
long id();
/**
* Returns the timestamp of when the session was created
*/
long creationTime();
/**
* Returns the timestamp of when the session will expire
*/
long expirationTime();
/**
* Returns version of the session.
* A session's version is incremented on each heartbeat.
*/
long version();
/**
* Returns true if the session expires before the given timestamp.
*/
boolean isExpired(long timestamp);
/**
* Returns the endpoint that has created this session
*/
Address endpoint();
/**
* Returns type of the endpoint that has created this session
*/
CPSessionOwnerType endpointType();
/**
* Returns name of the endpoint that has created this session
*/
String endpointName();
}