Java 16 Foreign-Memory Access API (Incubator, JEP 394)

Java 16 introduced an incubator module for the Foreign-Memory Access API, which is a new API that allows you to access and manipulate foreign memory from Java programs. The Foreign-Memory Access API is designed to provide a safe and efficient way to work with memory that is outside the Java heap, such as memory that is managed by native libraries or by other processes.

Here is an example of how to use the Foreign-Memory Access API in Java:

MemorySegment segment = MemorySegment.allocateNative(1024);
try (MemorySegmentAccess access = segment.forAccess(MemorySegment.READ_WRITE)) {
  long address = access.baseAddress();
  // Use the memory at address as if it were a native array
  for (int i = 0; i < 1024; i++) {
    Unsafe.getUnsafe().putByte(address + i, (byte) i);
  }
} finally {
  segment.close();
}

In this example, we are using the MemorySegment.allocateNative method to allocate a block of native memory with a size of 1024 bytes. We are then using the MemorySegment.forAccess method to create a MemorySegmentAccess object that allows us to read and write to the memory segment. The MemorySegmentAccess object provides a base address that we can use to access the memory as if it were a native array. Finally, we are using the Unsafe class to write a sequence of bytes to the memory segment, starting at the base address and incrementing the address by one for each byte.

The Foreign-Memory Access API provides a number of other features that can be useful for working with foreign memory, such as the ability to create memory segments from existing memory regions, the ability to share memory segments between threads and processes, and the ability to map memory segments to files or devices.

One important thing to note about the Foreign-Memory Access API is that it is currently an incubator module, which means that it is experimental and may change in future releases. It is also subject to additional restrictions and requirements, such as the need to enable the module explicitly and the need to comply with the terms of the Foreign-Memory Access API incubator module license.