org.apache.datasketches.memory.package-info Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of datasketches-memory Show documentation
High-performance native memory access.
The newest version!
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */

/**
 * This package provides high performance primitive and primitive array access to direct (native),
 * off-heap memory and memory-mapped file resources, and consistent views into
 * {@link java.nio.ByteBuffer}, and on-heap primitive arrays. It can be used as a more
 * comprehensive and flexible replacement for {@link java.nio.ByteBuffer}.
 * 
 *
 * In addition, this package provides:
 *
 * Two different access APIs: read-only {@link org.apache.datasketches.memory.Memory} and
 * {@link org.apache.datasketches.memory.WritableMemory} for absolute offset access,
 * and read-only {@link org.apache.datasketches.memory.Buffer} and
 * {@link org.apache.datasketches.memory.WritableBuffer}
 * for relative positional access (similar to ByteBuffer).
 *
 * Clean separation of Read-only API from Writable API, which makes writable versus read-only
 * resources detectable at compile time.
 *
 * The conversion from Writable to read-only is just a cast, so no unnecessary objects are
 * created. For example:
 *  *     WritableMemory wMem = ...
 *     Memory mem = wMem;
 * 
 * 
 *
 *  {@link java.lang.AutoCloseable} for the external resources that require it,
 * which enables compile-time checks for non-closed resources.
 *
 * Immediate invalidation of all downstream references of an AutoCloseable
 * resource when that resource is closed, either manually or by the JVM.
 * This virtually eliminates the possibility of accidentally writing into the memory space
 * previously owned by a closed resource.
 *
 * Improved performance over the prior Memory implementation.
 *
 * No external dependencies, which makes it simple to install in virtually any Java environment.
 * 
 * 
 *
 * More specifically, this package provides access to four different types of resources using
 * two different access APIs. These resources are contiguous blobs of bytes that provide at least
 * byte-level read and write access. The four resources are:
 *
 * Direct (a.k.a. Native) off-heap memory allocated by the user.
 * Memory-mapped files, both writable and read-only.
 * {@code ByteBuffers}, both heap-based and direct, writable and read-only.
 * Heap-based primitive arrays, which can be accessed as writable or read-only.
 * 
 *
 * The two different access APIs are:
 * Memory, WritableMemory: Absolute offset addressing into a resource.
 * Buffer, WritableBuffer: Position relative addressing into a resource.
 * 
 *
 * In addition, all combinations of access APIs and backing resources can be accessed via
 * multibyte primitive methods (e.g.
 * getLong(...), getLongArray(...), putLong(...), putLongArray(...)) as either
 * {@link java.nio.ByteOrder#BIG_ENDIAN} or {@link java.nio.ByteOrder#LITTLE_ENDIAN}.
 *
 * The resources don't know or care about the access APIs, and the access
 * APIs don't really know or care what resource they are accessing.
 *
 * An access API is joined with a resource with a static factory method.
 *
 *
Moving back and forth between Memory and Buffer:
 * *    Memory mem = ...
 *    Buffer buf = mem.asBuffer();
 *    ...
 *    Memory mem2 = buf.asMemory();
 *    ...
 * 
 *
 * Hierarchical memory regions can be easily created:
 *  *     WritableMemory wMem = ...
 *     WritableMemory wReg = wMem.writableRegion(offset, length); //OR
 *     Memory region = wMem.region(offset, length);
 * 
 *
 * @author Lee Rhodes
 */
package org.apache.datasketches.memory;