Module java.base
Package java.lang.foreign

Interface SegmentAllocator

All Known Subinterfaces:
Arena
Functional Interface:
This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
@FunctionalInterface public interface SegmentAllocator
An object that may be used to allocate memory segments. Clients implementing this interface must implement the allocate(long, long) method. A segment allocator defines several methods which can be useful to create segments from several kinds of Java values such as primitives and arrays.

SegmentAllocator is a functional interface. Clients can easily obtain a new segment allocator by using either a lambda expression or a method reference: 

SegmentAllocator autoAllocator = (byteSize, byteAlignment) -> Arena.ofAuto().allocate(byteSize, byteAlignment);

This interface defines factories for commonly used allocators:

Passing a segment allocator to an API can be especially useful in circumstances where a client wants to communicate where the results of a certain operation (performed by the API) should be stored, as a memory segment. For instance, downcall method handles can accept an additional SegmentAllocator parameter if the underlying foreign function is known to return a struct by-value. Effectively, the allocator parameter tells the linker where to store the return value of the foreign function.

Since:
22
API Note:
Unless otherwise specified, the allocate(long, long) method is not thread-safe. Furthermore, memory segments allocated by a segment allocator can be associated with different lifetimes, and can even be backed by overlapping regions of memory. For these reasons, clients should generally only interact with a segment allocator they own.

Clients should consider using an arena instead, which, provides strong thread-safety, lifetime and non-overlapping guarantees.

  • Method Summary

    Modifier and Type
    Method
    Description
    default MemorySegment
    allocate(long byteSize)
    Returns a new memory segment with the given byteSize.
    MemorySegment
    allocate(long byteSize, long byteAlignment)
    Returns a new memory segment with the given byteSize and byteAlignment.
    default MemorySegment
    allocate(MemoryLayout layout)
    Returns a new memory segment with the given layout.
    default MemorySegment
    allocate(MemoryLayout elementLayout, long count)
    Returns a new memory segment with the given elementLayout and count.
    default MemorySegment
    allocateFrom(AddressLayout layout, MemorySegment value)
    Returns a new memory segment initialized with the address of the provided value as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfByte layout, byte value)
    Returns a new memory segment initialized with the provided byte value as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfByte elementLayout, byte... elements)
    Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E byte elements as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfChar layout, char value)
    Returns a new memory segment initialized with the provided char value as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfChar elementLayout, char... elements)
    Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E char elements as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfDouble layout, double value)
    Returns a new memory segment initialized with the provided double value as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfDouble elementLayout, double... elements)
    Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E double elements as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfFloat layout, float value)
    Returns a new memory segment initialized with the provided float value as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfFloat elementLayout, float... elements)
    Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E float elements as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfInt layout, int value)
    Returns a new memory segment initialized with the provided int value as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfInt elementLayout, int... elements)
    Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E int elements as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfLong layout, long value)
    Returns a new memory segment initialized with the provided long value as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfLong elementLayout, long... elements)
    Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E long elements as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfShort layout, short value)
    Returns a new memory segment initialized with the provided short value as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(ValueLayout.OfShort elementLayout, short... elements)
    Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E short elements as specified by the provided layout (i.e. byte ordering, alignment and size).
    default MemorySegment
    allocateFrom(String str)
    Converts a Java string into a null-terminated C string using the UTF-8 charset, storing the result into a memory segment.
    default MemorySegment
    allocateFrom(String str, Charset charset)
    Converts a Java string into a null-terminated C string using the provided charset, and storing the result into a memory segment.
    static SegmentAllocator
    prefixAllocator(MemorySegment segment)
    Returns a segment allocator which responds to allocation requests by recycling a single segment.
    static SegmentAllocator
    slicingAllocator(MemorySegment segment)
    Returns a segment allocator which responds to allocation requests by returning consecutive slices obtained from the provided segment.

  • Method Details

    • allocateFrom

      default MemorySegment allocateFrom(String str)
      Converts a Java string into a null-terminated C string using the UTF-8 charset, storing the result into a memory segment.

      Calling this method is equivalent to the following code: 

       allocateFrom(str, StandardCharsets.UTF_8);
      Parameters:
      str - the Java string to be converted into a C string.
      Returns:
      a new native segment containing the converted C string.

    • allocateFrom

      default MemorySegment allocateFrom(String str, Charset charset)
      Converts a Java string into a null-terminated C string using the provided charset, and storing the result into a memory segment.

      This method always replaces malformed-input and unmappable-character sequences with this charset's default replacement byte array. The CharsetEncoder class should be used when more control over the encoding process is required.

      If the given string contains any '\0' characters, they will be copied as well. This means that, depending on the method used to read the string, such as MemorySegment.getString(long), the string will appear truncated when read again.

      Parameters:
      str - the Java string to be converted into a C string.
      charset - the charset used to encode the string bytes.
      Returns:
      a new native segment containing the converted C string.
      Throws:
      UnsupportedOperationException - if charset is not a standard charset.
      Implementation Requirements:
      The default implementation for this method copies the contents of the provided Java string into a new memory segment obtained by calling this.allocate(B + N), where:
      • B is the size, in bytes, of the string encoded using the provided charset (e.g. str.getBytes(charset).length);
      • N is the size (in bytes) of the terminator char according to the provided charset. For instance, this is 1 for StandardCharsets.US_ASCII and 2 for StandardCharsets.UTF_16.

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfByte layout, byte value)
      Returns a new memory segment initialized with the provided byte value as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      layout - the layout of the block of memory to be allocated.
      value - the value to be set in the newly allocated memory segment.
      Returns:
      a new memory segment initialized with the provided byte value as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfChar layout, char value)
      Returns a new memory segment initialized with the provided char value as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      layout - the layout of the block of memory to be allocated.
      value - the value to be set in the newly allocated memory segment.
      Returns:
      a new memory segment initialized with the provided char value as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfShort layout, short value)
      Returns a new memory segment initialized with the provided short value as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      layout - the layout of the block of memory to be allocated.
      value - the value to be set in the newly allocated memory segment.
      Returns:
      a new memory segment initialized with the provided short value as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfInt layout, int value)
      Returns a new memory segment initialized with the provided int value as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      layout - the layout of the block of memory to be allocated.
      value - the value to be set in the newly allocated memory segment.
      Returns:
      a new memory segment initialized with the provided int value as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfFloat layout, float value)
      Returns a new memory segment initialized with the provided float value as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      layout - the layout of the block of memory to be allocated.
      value - the value to be set in the newly allocated memory segment.
      Returns:
      a new memory segment initialized with the provided float value as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfLong layout, long value)
      Returns a new memory segment initialized with the provided long value as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      layout - the layout of the block of memory to be allocated.
      value - the value to be set in the newly allocated memory segment.
      Returns:
      a new memory segment initialized with the provided long value as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfDouble layout, double value)
      Returns a new memory segment initialized with the provided double value as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      layout - the layout of the block of memory to be allocated.
      value - the value to be set in the newly allocated memory segment.
      Returns:
      a new memory segment initialized with the provided double value as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(AddressLayout layout, MemorySegment value)
      Returns a new memory segment initialized with the address of the provided value as specified by the provided layout (i.e. byte ordering, alignment and size).

      The address value might be narrowed according to the platform address size (see ValueLayout.ADDRESS).

      Parameters:
      layout - the layout of the block of memory to be allocated.
      value - the value to be set in the newly allocated memory segment.
      Returns:
      a new memory segment initialized with the address of the provided value as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       Objects.requireNonNull(value);
 MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfByte elementLayout, byte... elements)
      Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E byte elements as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the short elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E byte elements as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       int size = Objects.requireNonNull(elements).length;
 MemorySegment seg = allocateArray(Objects.requireNonNull(elementLayout), size);
 MemorySegment.copy(elements, 0, seg, elementLayout, 0, size);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfShort elementLayout, short... elements)
      Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E short elements as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the short elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E short elements as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       int size = Objects.requireNonNull(elements).length;
 MemorySegment seg = allocateArray(Objects.requireNonNull(elementLayout), size);
 MemorySegment.copy(elements, 0, seg, elementLayout, 0, size);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfChar elementLayout, char... elements)
      Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E char elements as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the short elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E char elements as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       int size = Objects.requireNonNull(elements).length;
 MemorySegment seg = allocateArray(Objects.requireNonNull(elementLayout), size);
 MemorySegment.copy(elements, 0, seg, elementLayout, 0, size);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfInt elementLayout, int... elements)
      Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E int elements as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the short elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E int elements as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       int size = Objects.requireNonNull(elements).length;
 MemorySegment seg = allocateArray(Objects.requireNonNull(elementLayout), size);
 MemorySegment.copy(elements, 0, seg, elementLayout, 0, size);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfFloat elementLayout, float... elements)
      Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E float elements as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the short elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E float elements as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       int size = Objects.requireNonNull(elements).length;
 MemorySegment seg = allocateArray(Objects.requireNonNull(elementLayout), size);
 MemorySegment.copy(elements, 0, seg, elementLayout, 0, size);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfLong elementLayout, long... elements)
      Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E long elements as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the short elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E long elements as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       int size = Objects.requireNonNull(elements).length;
 MemorySegment seg = allocateArray(Objects.requireNonNull(elementLayout), size);
 MemorySegment.copy(elements, 0, seg, elementLayout, 0, size);
 return seg;

    • allocateFrom

      default MemorySegment allocateFrom(ValueLayout.OfDouble elementLayout, double... elements)
      Returns a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E double elements as specified by the provided layout (i.e. byte ordering, alignment and size).
      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the short elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment with a byteSize() of E*layout.byteSize() initialized with the provided E double elements as specified by the provided layout (i.e. byte ordering, alignment and size)
      Implementation Requirements:
      The default implementation is equivalent to: 
       int size = Objects.requireNonNull(elements).length;
 MemorySegment seg = allocateArray(Objects.requireNonNull(elementLayout), size);
 MemorySegment.copy(elements, 0, seg, elementLayout, 0, size);
 return seg;

    • allocate

      default MemorySegment allocate(MemoryLayout layout)
      Returns a new memory segment with the given layout.
      Parameters:
      layout - the layout of the block of memory to be allocated.
      Returns:
      a new memory segment with the given layout
      Implementation Requirements:
      The default implementation for this method calls this.allocate(layout.byteSize(), layout.byteAlignment()).

    • allocate

      default MemorySegment allocate(MemoryLayout elementLayout, long count)
      Returns a new memory segment with the given elementLayout and count.
      Parameters:
      elementLayout - the array element layout.
      count - the array element count.
      Returns:
      a new memory segment with the given elementLayout and count
      Throws:
      IllegalArgumentException - if elementLayout.byteSize() * count overflows.
      IllegalArgumentException - if count < 0.
      Implementation Requirements:
      The default implementation for this method calls this.allocate(MemoryLayout.sequenceLayout(count, elementLayout)).

    • allocate

      default MemorySegment allocate(long byteSize)
      Returns a new memory segment with the given byteSize.
      Parameters:
      byteSize - the size (in bytes) of the block of memory to be allocated.
      Returns:
      a new memory segment with the given byteSize
      Throws:
      IllegalArgumentException - if byteSize < 0
      Implementation Requirements:
      The default implementation for this method calls this.allocate(byteSize, 1).

    • allocate

      MemorySegment allocate(long byteSize, long byteAlignment)
      Returns a new memory segment with the given byteSize and byteAlignment.
      Parameters:
      byteSize - the size (in bytes) of the block of memory to be allocated.
      byteAlignment - the alignment (in bytes) of the block of memory to be allocated.
      Returns:
      a new memory segment with the given byteSize and byteAlignment
      Throws:
      IllegalArgumentException - if byteSize < 0, byteAlignment <= 0, or if byteAlignment is not a power of 2.

    • slicingAllocator

      static SegmentAllocator slicingAllocator(MemorySegment segment)
      Returns a segment allocator which responds to allocation requests by returning consecutive slices obtained from the provided segment. Each new allocation request will return a new slice starting at the current offset (modulo additional padding to satisfy alignment constraint), with given size.

      The returned allocator throws IndexOutOfBoundsException when a slice of the provided segment with the requested size and alignment cannot be found.

      Parameters:
      segment - the segment which the returned allocator should slice from.
      Returns:
      a new slicing allocator
      Implementation Note:
      A slicing allocator is not thread-safe.

    • prefixAllocator

      static SegmentAllocator prefixAllocator(MemorySegment segment)
      Returns a segment allocator which responds to allocation requests by recycling a single segment. Each new allocation request will return a new slice starting at the segment offset 0, hence the name prefix allocator. Equivalent to (but likely more efficient than) the following code: 
      MemorySegment segment = ...
SegmentAllocator prefixAllocator = (size, align) -> segment.asSlice(0, size, align);
      The returned allocator throws IndexOutOfBoundsException when a slice of the provided segment with the requested size and alignment cannot be found.
      Parameters:
      segment - the memory segment to be recycled by the returned allocator.
      Returns:
      an allocator which recycles an existing segment upon each new allocation request.
      API Note:
      A prefix allocator can be useful to limit allocation requests in case a client knows that they have fully processed the contents of the allocated segment before the subsequent allocation request takes place.
      Implementation Note:
      While a prefix allocator is thread-safe, concurrent access on the same recycling allocator might cause a thread to overwrite contents written to the underlying segment by a different thread.