Class SequenceLayout

java.lang.Object
jdk.incubator.foreign.SequenceLayout
All Implemented Interfaces:
Constable, MemoryLayout

public final class SequenceLayout
extends Object
A sequence layout. A sequence layout is used to denote a repetition of a given layout, also called the sequence layout's element layout. The repetition count, where it exists (e.g. for finite sequence layouts) is said to be the the sequence layout's element count. A finite sequence layout can be thought of as a group layout where the sequence layout's element layout is repeated a number of times that is equal to the sequence layout's element count. In other words this layout:

MemoryLayout.ofSequence(3, MemoryLayout.ofValueBits(32, ByteOrder.BIG_ENDIAN));
 
is equivalent to the following layout:

MemoryLayout.ofStruct(
    MemoryLayout.ofValueBits(32, ByteOrder.BIG_ENDIAN),
    MemoryLayout.ofValueBits(32, ByteOrder.BIG_ENDIAN),
    MemoryLayout.ofValueBits(32, ByteOrder.BIG_ENDIAN));
 

This is a value-based class; use of identity-sensitive operations (including reference equality (==), identity hash code, or synchronization) on instances of SequenceLayout may have unpredictable results and should be avoided. The equals method should be used for comparisons.

Implementation Requirements:
This class is immutable and thread-safe.
  • Method Details

    • elementLayout

      public MemoryLayout elementLayout()
      Returns the element layout associated with this sequence layout.
      Returns:
      The element layout associated with this sequence layout.
    • elementCount

      public OptionalLong elementCount()
      Returns the element count of this sequence layout (if any).
      Returns:
      the element count of this sequence layout (if any).
    • withElementCount

      public SequenceLayout withElementCount​(long elementCount)
      Obtains a new sequence layout with same element layout, alignment constraints and name as this sequence layout but with the new specified element count.
      Parameters:
      elementCount - the new element count.
      Returns:
      a new sequence with given element count.
      Throws:
      IllegalArgumentException - if elementCount < 0.
    • reshape

      public SequenceLayout reshape​(long... elementCounts)
      Returns a new sequence layout where element layouts in the flattened projection of this sequence layout (see flatten()) are re-arranged into one or more nested sequence layouts according to the provided element counts. This transformation preserves the layout size; that is, multiplying the provided element counts must yield the same element count as the flattened projection of this sequence layout.

      For instance, given a sequence layout of the kind:

      
          var seq = MemoryLayout.ofSequence(4, MemoryLayout.ofSequence(3, MemoryLayouts.JAVA_INT));
       
      calling seq.reshape(2, 6) will yield the following sequence layout:
      
          var reshapeSeq = MemoryLayout.ofSequence(2, MemoryLayout.ofSequence(6, MemoryLayouts.JAVA_INT));
       

      If one of the provided element count is the special value -1, then the element count in that position will be inferred from the remaining element counts and the element count of the flattened projection of this layout. For instance, a layout equivalent to the above reshapeSeq can also be computed in the following ways:

      
          var reshapeSeqImplicit1 = seq.reshape(-1, 6);
          var reshapeSeqImplicit2 = seq.reshape(2, -1);
       
      Parameters:
      elementCounts - an array of element counts, of which at most one can be -1.
      Returns:
      a new sequence layout where element layouts in the flattened projection of this sequence layout (see flatten()) are re-arranged into one or more nested sequence layouts.
      Throws:
      NullPointerException - if elementCounts == null.
      UnsupportedOperationException - if this sequence layout does not have an element count.
      IllegalArgumentException - if two or more element counts are set to -1, or if one or more element count is <= 0 (but other than -1) or, if, after any required inference, multiplying the element counts does not yield the same element count as the flattened projection of this sequence layout.
    • flatten

      public SequenceLayout flatten()
      Returns a new, flattened sequence layout whose element layout is the first non-sequence element layout found by recursively traversing the element layouts of this sequence layout. This transformation preserves the layout size; nested sequence layout in this sequence layout will be dropped and their element counts will be incorporated into that of the returned sequence layout. For instance, given a sequence layout of the kind:
      
          var seq = MemoryLayout.ofSequence(4, MemoryLayout.ofSequence(3, MemoryLayouts.JAVA_INT));
       
      calling seq.flatten() will yield the following sequence layout:
      
          var flattenedSeq = MemoryLayout.ofSequence(12, MemoryLayouts.JAVA_INT);
       
      Returns:
      a new sequence layout with the same size as this layout (but, possibly, with different element count), whose element layout is not a sequence layout.
      Throws:
      UnsupportedOperationException - if this sequence layout, or one of the nested sequence layouts being flattened, does not have an element count.
    • equals

      public boolean equals​(Object other)
      Description copied from class: Object
      Indicates whether some other object is "equal to" this one.

      The equals method implements an equivalence relation on non-null object references:

      • It is reflexive: for any non-null reference value x, x.equals(x) should return true.
      • It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
      • It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
      • It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
      • For any non-null reference value x, x.equals(null) should return false.

      The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

      Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

      Specified by:
      equals in interface MemoryLayout
      Parameters:
      other - the reference object with which to compare.
      Returns:
      true if this object is the same as the obj argument; false otherwise.
      See Also:
      Object.hashCode(), HashMap
    • hashCode

      public int hashCode()
      Description copied from class: Object
      Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.

      The general contract of hashCode is:

      • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
      • If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
      • It is not required that if two objects are unequal according to the Object.equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.
      Specified by:
      hashCode in interface MemoryLayout
      Returns:
      a hash code value for this object.
      See Also:
      Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)
    • describeConstable

      public Optional<DynamicConstantDesc<SequenceLayout>> describeConstable()
      Description copied from interface: MemoryLayout
      Returns an Optional containing the nominal descriptor for this layout, if one can be constructed, or an empty Optional if one cannot be constructed.
      Returns:
      An Optional containing the resulting nominal descriptor, or an empty Optional if one cannot be constructed.
    • withName

      public SequenceLayout withName​(String name)
      Creates a new layout which features the desired layout name.

      This is equivalent to the following code:

      
          withAttribute(LAYOUT_NAME, name);
       
      Specified by:
      withName in interface MemoryLayout
      Parameters:
      name - the layout name.
      Returns:
      a new layout which is the same as this layout, except for the name associated to it.
      See Also:
      MemoryLayout.name()
    • withBitAlignment

      public SequenceLayout withBitAlignment​(long alignmentBits)
      Creates a new layout which features the desired alignment constraint.
      Specified by:
      withBitAlignment in interface MemoryLayout
      Parameters:
      alignmentBits - the layout alignment constraint, expressed in bits.
      Returns:
      a new layout which is the same as this layout, except for the alignment constraint associated to it.
    • withAttribute

      public SequenceLayout withAttribute​(String name, Constable value)
      Returns a new memory layout which features the same attributes as this layout, plus the newly specified attribute. If this layout already contains an attribute with the same name, the existing attribute value is overwritten in the returned layout.
      Specified by:
      withAttribute in interface MemoryLayout
      Parameters:
      name - the attribute name.
      value - the attribute value.
      Returns:
      a new memory layout which features the same attributes as this layout, plus the newly specified attribute.
    • name

      public final Optional<String> name()
      Description copied from interface: MemoryLayout
      Return the name (if any) associated with this layout.

      This is equivalent to the following code:

      
          attribute(LAYOUT_NAME).map(String.class::cast);
       
      Specified by:
      name in interface MemoryLayout
      Returns:
      the layout name (if any).
      See Also:
      MemoryLayout.withName(String)
    • attribute

      public Optional<Constable> attribute​(String name)
      Description copied from interface: MemoryLayout
      Returns the attribute with the given name (if it exists).
      Specified by:
      attribute in interface MemoryLayout
      Parameters:
      name - the attribute name
      Returns:
      the attribute with the given name (if it exists).
    • attributes

      public Stream<String> attributes()
      Description copied from interface: MemoryLayout
      Returns a stream of the attribute names associated with this layout.
      Specified by:
      attributes in interface MemoryLayout
      Returns:
      a stream of the attribute names associated with this layout.
    • bitAlignment

      public final long bitAlignment()
      Description copied from interface: MemoryLayout
      Returns the alignment constraint associated with this layout, expressed in bits. Layout alignment defines a power of two A which is the bit-wise alignment of the layout. If A <= 8 then A/8 is the number of bytes that must be aligned for any pointer that correctly points to this layout. Thus:
      • A=8 means unaligned (in the usual sense), which is common in packets.
      • A=64 means word aligned (on LP64), A=32 int aligned, A=16 short aligned, etc.
      • A=512 is the most strict alignment required by the x86/SV ABI (for AVX-512 data).
      If no explicit alignment constraint was set on this layout (see MemoryLayout.withBitAlignment(long)), then this method returns the natural alignment constraint (in bits) associated with this layout.
      Specified by:
      bitAlignment in interface MemoryLayout
      Returns:
      the layout alignment constraint, in bits.
    • hasSize

      public boolean hasSize()
      Description copied from interface: MemoryLayout
      Does this layout have a specified size? A layout does not have a specified size if it is (or contains) a sequence layout whose size is unspecified (see elementCount()). Value layouts (see ValueLayout) and padding layouts (see MemoryLayout.ofPaddingBits(long)) always have a specified size, therefore this method always returns true in these cases.
      Specified by:
      hasSize in interface MemoryLayout
      Returns:
      true, if this layout has a specified size.
    • bitSize

      public long bitSize()
      Description copied from interface: MemoryLayout
      Computes the layout size, in bits.
      Specified by:
      bitSize in interface MemoryLayout
      Returns:
      the layout size, in bits.
    • isPadding

      public boolean isPadding()
      Description copied from interface: MemoryLayout
      Is this a padding layout (e.g. a layout created from MemoryLayout.ofPaddingBits(long)) ?
      Specified by:
      isPadding in interface MemoryLayout
      Returns:
      true, if this layout is a padding layout.