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 Details Link icon

    • allocateFrom Link icon

      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 Link icon

      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:
      IllegalArgumentException - 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 Link icon

      default MemorySegment allocateFrom(ValueLayout.OfByte layout, byte value)
      Returns a new memory segment initialized with the provided byte value..

      The size of the allocated memory segment is the size of the given layout. The given value is written into the segment according to the byte order and alignment constraint of the given layout.

      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.
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfChar layout, char value)
      Returns a new memory segment initialized with the provided char value..

      The size of the allocated memory segment is the size of the given layout. The given value is written into the segment according to the byte order and alignment constraint of the given layout.

      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.
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfShort layout, short value)
      Returns a new memory segment initialized with the provided short value..

      The size of the allocated memory segment is the size of the given layout. The given value is written into the segment according to the byte order and alignment constraint of the given layout.

      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.
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfInt layout, int value)
      Returns a new memory segment initialized with the provided int value..

      The size of the allocated memory segment is the size of the given layout. The given value is written into the segment according to the byte order and alignment constraint of the given layout.

      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.
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfFloat layout, float value)
      Returns a new memory segment initialized with the provided float value..

      The size of the allocated memory segment is the size of the given layout. The given value is written into the segment according to the byte order and alignment constraint of the given layout.

      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.
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfLong layout, long value)
      Returns a new memory segment initialized with the provided long value..

      The size of the allocated memory segment is the size of the given layout. The given value is written into the segment according to the byte order and alignment constraint of the given layout.

      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.
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfDouble layout, double value)
      Returns a new memory segment initialized with the provided double value..

      The size of the allocated memory segment is the size of the given layout. The given value is written into the segment according to the byte order and alignment constraint of the given layout.

      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.
      Implementation Requirements:
      The default implementation is equivalent to: 
       MemorySegment seg = allocate(Objects.requireNonNull(layout));
 seg.set(layout, 0, value);
 return seg;

    • allocateFrom Link icon

      default MemorySegment allocateFrom(AddressLayout layout, MemorySegment value)
      Returns a new memory segment initialized with the address of the provided memory segment..

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

      The size of the allocated memory segment is the size of the given layout. The given value is written into the segment according to the byte order and alignment constraint of the given layout.

      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 memory segment.
      Throws:
      UnsupportedOperationException - if value is not a native segment.
      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 Link icon

      default MemorySegment allocateFrom(ValueLayout elementLayout, MemorySegment source, ValueLayout sourceElementLayout, long sourceOffset, long elementCount)
      Returns a new memory segment initialized with the contents of the provided segment..

      The size of the allocated memory segment is the elementLayout.byteSize() * elementCount. The contents of the source segment is copied into the result segment element by element, according to the byte order and alignment constraint of the given element layout.

      Parameters:
      elementLayout - the element layout of the allocated array.
      source - the source segment.
      sourceElementLayout - the element layout of the source segment.
      sourceOffset - the starting offset, in bytes, of the source segment.
      elementCount - the number of elements in the source segment to be copied.
      Returns:
      a new memory segment initialized with the contents of the provided segment.
      Throws:
      IllegalArgumentException - if elementLayout.byteSize() != sourceElementLayout.byteSize().
      IllegalArgumentException - if the source segment/offset are incompatible with the alignment constraint in the source element layout.
      IllegalArgumentException - if elementLayout.byteAlignment() > elementLayout.byteSize().
      IllegalArgumentException - if sourceElementLayout.byteAlignment() > sourceElementLayout.byteSize().
      IllegalStateException - if the scope associated with source is not alive.
      WrongThreadException - if this method is called from a thread T, such that source.isAccessibleBy(T) == false.
      IndexOutOfBoundsException - if elementCount * sourceElementLayout.byteSize() overflows.
      IndexOutOfBoundsException - if sourceOffset > source.byteSize() - (elementCount * sourceElementLayout.byteSize()).
      IndexOutOfBoundsException - if either sourceOffset or elementCount are < 0.
      Implementation Requirements:
      the default implementation for this method is equivalent to the following code: 
      MemorySegment dest = this.allocate(elementLayout, elementCount);
MemorySegment.copy(source, sourceElementLayout, sourceOffset, dest, elementLayout, 0, elementCount);
return dest;

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfByte elementLayout, byte... elements)
      Returns a new memory segment initialized with the elements in the provided byte array..

      The size of the allocated memory segment is elementLayout.byteSize() * elements.length. The contents of the source array is copied into the result segment element by element, according to the byte order and alignment constraint of the given element layout.

      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the byte elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment initialized with the elements in the provided byte array.
      Throws:
      IllegalArgumentException - if elementLayout.byteAlignment() > elementLayout.byteSize().
      Implementation Requirements:
      the default implementation for this method is equivalent to the following code: 
       this.allocateFrom(layout, MemorySegment.ofArray(array),
                   ValueLayout.JAVA_BYTE, 0, array.length)

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfShort elementLayout, short... elements)
      Returns a new memory segment initialized with the elements in the provided short array..

      The size of the allocated memory segment is elementLayout.byteSize() * elements.length. The contents of the source array is copied into the result segment element by element, according to the byte order and alignment constraint of the given element layout.

      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 initialized with the elements in the provided short array.
      Throws:
      IllegalArgumentException - if elementLayout.byteAlignment() > elementLayout.byteSize().
      Implementation Requirements:
      the default implementation for this method is equivalent to the following code: 
       this.allocateFrom(layout, MemorySegment.ofArray(array),
                   ValueLayout.JAVA_SHORT, 0, array.length)

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfChar elementLayout, char... elements)
      Returns a new memory segment initialized with the elements in the provided char array..

      The size of the allocated memory segment is elementLayout.byteSize() * elements.length. The contents of the source array is copied into the result segment element by element, according to the byte order and alignment constraint of the given element layout.

      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the char elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment initialized with the elements in the provided char array.
      Throws:
      IllegalArgumentException - if elementLayout.byteAlignment() > elementLayout.byteSize().
      Implementation Requirements:
      the default implementation for this method is equivalent to the following code: 
       this.allocateFrom(layout, MemorySegment.ofArray(array),
                   ValueLayout.JAVA_CHAR, 0, array.length)

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfInt elementLayout, int... elements)
      Returns a new memory segment initialized with the elements in the provided int array..

      The size of the allocated memory segment is elementLayout.byteSize() * elements.length. The contents of the source array is copied into the result segment element by element, according to the byte order and alignment constraint of the given element layout.

      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the int elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment initialized with the elements in the provided int array.
      Throws:
      IllegalArgumentException - if elementLayout.byteAlignment() > elementLayout.byteSize().
      Implementation Requirements:
      the default implementation for this method is equivalent to the following code: 
       this.allocateFrom(layout, MemorySegment.ofArray(array),
                   ValueLayout.JAVA_INT, 0, array.length)

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfFloat elementLayout, float... elements)
      Returns a new memory segment initialized with the elements in the provided float array..

      The size of the allocated memory segment is elementLayout.byteSize() * elements.length. The contents of the source array is copied into the result segment element by element, according to the byte order and alignment constraint of the given element layout.

      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the float elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment initialized with the elements in the provided float array.
      Throws:
      IllegalArgumentException - if elementLayout.byteAlignment() > elementLayout.byteSize().
      Implementation Requirements:
      the default implementation for this method is equivalent to the following code: 
       this.allocateFrom(layout, MemorySegment.ofArray(array),
                   ValueLayout.JAVA_FLOAT, 0, array.length)

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfLong elementLayout, long... elements)
      Returns a new memory segment initialized with the elements in the provided long array..

      The size of the allocated memory segment is elementLayout.byteSize() * elements.length. The contents of the source array is copied into the result segment element by element, according to the byte order and alignment constraint of the given element layout.

      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the long elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment initialized with the elements in the provided long array.
      Throws:
      IllegalArgumentException - if elementLayout.byteAlignment() > elementLayout.byteSize().
      Implementation Requirements:
      the default implementation for this method is equivalent to the following code: 
       this.allocateFrom(layout, MemorySegment.ofArray(array),
                   ValueLayout.JAVA_LONG, 0, array.length)

    • allocateFrom Link icon

      default MemorySegment allocateFrom(ValueLayout.OfDouble elementLayout, double... elements)
      Returns a new memory segment initialized with the elements in the provided double array..

      The size of the allocated memory segment is elementLayout.byteSize() * elements.length. The contents of the source array is copied into the result segment element by element, according to the byte order and alignment constraint of the given element layout.

      Parameters:
      elementLayout - the element layout of the array to be allocated.
      elements - the double elements to be copied to the newly allocated memory block.
      Returns:
      a new memory segment initialized with the elements in the provided double array.
      Throws:
      IllegalArgumentException - if elementLayout.byteAlignment() > elementLayout.byteSize().
      Implementation Requirements:
      the default implementation for this method is equivalent to the following code: 
       this.allocateFrom(layout, MemorySegment.ofArray(array),
                   ValueLayout.JAVA_DOUBLE, 0, array.length)

    • allocate Link icon

      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 Link icon

      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 Link icon

      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 Link icon

      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 Link icon

      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 Link icon

      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.