Off-heap memory tools based on sun.misc.Unsafe

Some tools to work with off-heap memory using sun.misc.Unsafe class. Contains fallback implementations for environments, where proper implementation of sun.misc.Unsafe is not available.

All memory access code has boundary checks using assert keyword. With assertions enabled in runtime (-ea java switch) illegal memory access will throw AssertionError. Without assertions illegal memory access will crash JVM.

Library has no third-party dependencies and is available in Maven central:

<dependency>
    <groupId>com.alexkasko.unsafe</groupId>
    <artifactId>unsafe-tools</artifactId>
    <version>1.3.3</version>
</dependency>

Off-heap memory, data structures, operations

JVM allows to allocate and use memory outside of java heap. Such off-heap memory may be allocated/used/deallocated without additional load on garbage collector.

###Off-heap memory management

Off-heap memory manager implemented as a thin wrapper over sun.misc.Unsafe. Other data structures implemented on top of it.

See com.alexkasko.unsafe.offheap package description for details.

###Off-heap collections of longs

Maximum array length in Java is bounded by Integer.MAX_VALUE. This library provides long-sized fixed and growing arrays of longs.

See com.alexkasko.unsafe.offheaplong package description for details.

###Off-heap collections of structs (memory areas)

Equal-sized memory areas may be stored in off-heap memory contiguously as collections. Such memory areas also may be used like C structs (without compiler checks, though). Sorting and searching of these collections may be done using arbitrary "fields" of such "structs".

See com.alexkasko.unsafe.offheapstruct package description for details.

###Off-heap header-payload collections

Note: header-payload collections were deprecated in favor of struct collections.

In header-payload collections each element contains long header (which is used for sorting and searching) and an additional payload. Payloads are stored in memory next to headers. Byte arrays of arbitrary size may be used as payloads for storing non-primitive values. Special collections for long and int payloads should be faster than byte[] ones.

###Operations

Next operations are implemented for all off-heap data structures:

• Dual-Pivot Quicksort implementation, adapted from here.
• Binary Search implementation, adapted from here.

Byte array tool

sun.misc.Unsafe may be used for writing/reading primitive values to/from byte arrays and to copying memory between byte arrays. Byte array tool is implemented on top of it.

See com.alexkasko.unsafe.bytearray package description for details.

License information

This project is released under the Apache License 2.0

Changelog

1.3.3 (2013-08-13)

• sorting struct collections using unsigned fields comparison

1.3.2 (2013-08-08)

• fix sort of empty struct collection using multiple keys

1.3.1 (2013-07-08)

• struct collections sorting using short and byte fields
• struct collections sorting with multiple keys

1.3.0 (2013-07-07)

• packages changed
• struct collectons added
• payload collections deprecated

1.2.4 (2013-05-21)

• more strict checks for lists set
• setPayload method added

1.2.3 (2013-05-06)

• improve assert checks for off-heap memory
• binary search javadoc fixes

1.2.2 (2013-04-28)

• prevent result object instantiation in ranged search

1.2.1 (2013-04-28)

• ranges support for binary search

1.2 (2013-04-25)

• bug fixed in OffHeapPayloadSorter - in some circumstances in 1.1 sorting may overwrite payload values for equal headers. A lot of tests on random data have been run to check correctness of 1.2 version
• header-int_payload array, array list and sorting
• header-long_payload array, array list and sorting

1.1 (2013-03-05)

• long-array list
• header-payload array and array list
• binary search for all collections

1.0 (2013-02-24)

• initial version