Interface Summary
Interface	Description
OffHeapAddressable	Basic interface for off-heap long-indexed collections.
OffHeapDisposable	Basic interface for off-heap classes that support manual memory freeing.
OffHeapDisposableIterable<T>	Interface for iterables over off-heap collections those can be disposed manually
OffHeapDisposableIterator<T>	Interface for iterators over off-heap collections those can be disposed manually

Class Summary
Class	Description
DirectOffHeapMemory	Implementation of `OffHeapMemory` using `ByteBuffer.allocateDirect(int)`
OffHeapMemory	Allocates an area of off-heap memory that is not a subject to GC.
OffHeapUtils	Static utility methods for off-heap classes
OffHeapUtils.EmptyDisposableIterator<T>	Returns empty instance of `OffHeapDisposableIterator`
OnHeapMemory	Implementation of `OffHeapMemory` using byte array effectively making it OnHeap memory
UnsafeOffHeapMemory	Implementation of `OffHeapMemory` using `sun.misc.Unsafe`

Package com.alexkasko.unsafe.offheap Description

Off-heap memory operations using sun.misc.Unsafe

This package contains OffHeapMemory frontend class for working with off-heap memory: allocation, immediate deallocation, reading/writing primitives and byte arrays.

Implementations

Main implementation (UnsafeOffHeapMemory) uses Unsafe, fallback implementation (DirectOffHeapMemory) uses DirectByteBuffers, additional on-heap implementation (OnHeapMemory) uses byte arrays.

Boundary checks

With Unsafe backend all operations have boundary checks using assert keyword. With assertions enabled in runtime (-ea java switch) illegal memory access will thow AssertionError. Without assertions illegal memory access will crash JVM.

Fallback implementation

Fallback implementation have some drawbacks comparing with unsafe one:

mandatory boundary checks
each memory allocation is limited by Integer.MAX_VALUE
by default off-heap memory is freed only when DirectByteBuffer is garbage collector; this library uses reflection hacks (different for OpenJDK and Android implementations) to free memory eagerly

On-heap implementation

On-heap implementation added for rare cases when the same API is required for small on-heap collection. It may not allocate more than Integer.MAX_VALUE memory.

Data structures

OffHeapMemory is used as a base for off-heap data structures, see com.alexkasko.unsafe.offheaplong and com.alexkasko.unsafe.offheapstruct packages.

Additional utility classes

OffHeapUtils: allows freeing memory quietly checking null on provided instance
OffHeapDisposable: interface for freeable classes

Usage example (in tests): github link