/*
* 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.
*
* Contributions from 2013-2017 where performed either by US government
* employees, or under US Veterans Health Administration contracts.
*
* US Veterans Health Administration contributions by government employees
* are work of the U.S. Government and are not subject to copyright
* protection in the United States. Portions contributed by government
* employees are USGovWork (17USC ยง105). Not subject to copyright.
*
* Contribution by contractors to the US Veterans Health Administration
* during this period are contractually contributed under the
* Apache License, Version 2.0.
*
* See: https://www.usa.gov/government-works
*
* Contributions prior to 2013:
*
* Copyright (C) International Health Terminology Standards Development Organisation.
* Licensed under the Apache License, Version 2.0.
*
*/
/**
* CAS on objects utilizes the object pointer (identity) to determine
* if the current value == the expected value.
*
* The original object is a byte array, where the 1st 64 bits is a long
* value that provides an object version identifier.
*
* To write an updated object, perform a get, then compare the 1st 64 bits with
* the first 64 bits of the object to be written. If they are the same, then there
* have been no writes between when the new object was read, and write of the
* new object can proceed without a merge.
*
* If they are not the same, then the objects must be merged, and then write attempted again.
*
* Write sequences can be allocated in parallel based on a modulus of the object key,
* as a key to the sequence allocator.
*
* Each version has a stamp, and these stamps uniquely identify the versions, and
* merger can be performed by creating a set union of the versions as identified by
* their stamps.
*
* Fields:
* Write sequence
* Native ID
* Container Sequence
* stamp
* length
* data...
* stamp
* length
* data...
* stamp // if stamp < 0; then end of record.
*/
package sh.isaac.model.waitfree;