Interface MemorySegment

Method Details

• address

  MemoryAddress address()

  The base memory address associated with this memory segment. The returned memory address is associated with same resource scope as that associated with this segment.

  Specified by:

  address in interface Addressable

  Returns:

  The base memory address.

• spliterator

  Spliterator<MemorySegment> spliterator(MemoryLayout elementLayout)

  Returns a spliterator for this memory segment. The returned spliterator reports Spliterator.SIZED, Spliterator.SUBSIZED, Spliterator.IMMUTABLE, Spliterator.NONNULL and Spliterator.ORDERED characteristics.

  The returned spliterator splits this segment according to the specified element layout; that is, if the supplied layout has size N, then calling Spliterator.trySplit() will result in a spliterator serving approximately S/N/2 elements (depending on whether N is even or not), where S is the size of this segment. As such, splitting is possible as long as S/N >= 2. The spliterator returns segments that feature the same scope as this given segment.

  The returned spliterator effectively allows to slice this segment into disjoint sub-segments, which can then be processed in parallel by multiple threads.

  Parameters:

  elementLayout - the layout to be used for splitting.

  Returns:

  the element spliterator for this segment

  Throws:

  IllegalArgumentException - if the elementLayout size is zero, or the segment size modulo the elementLayout size is greater than zero.

• elements

  Stream<MemorySegment> elements(MemoryLayout elementLayout)

  Returns a sequential Stream over disjoint slices (whose size matches that of the specified layout) in this segment. Calling this method is equivalent to the following code:

  
      StreamSupport.stream(segment.spliterator(elementLayout), false);
   

  Parameters:

  elementLayout - the layout to be used for splitting.

  Returns:

  a sequential Stream over disjoint slices in this segment.

  Throws:

  IllegalArgumentException - if the elementLayout size is zero, or the segment size modulo the elementLayout size is greater than zero.

• scope

  ResourceScope scope()

  Returns the resource scope associated with this memory segment.

  Returns:

  the resource scope associated with this memory segment.

• byteSize

  long byteSize()

  The size (in bytes) of this memory segment.

  Returns:

  The size (in bytes) of this memory segment.

• asSlice

  MemorySegment asSlice(long offset, long newSize)

  Obtains a new memory segment view whose base address is the same as the base address of this segment plus a given offset, and whose new size is specified by the given argument.

  Parameters:

  offset - The new segment base offset (relative to the current segment base address), specified in bytes.

  newSize - The new segment size, specified in bytes.

  Returns:

  a new memory segment view with updated base/limit addresses.

  Throws:

  IndexOutOfBoundsException - if offset < 0, offset > byteSize(), newSize < 0, or newSize > byteSize() - offset

  See Also:

  • asSlice(long)
  • asSlice(MemoryAddress)
  • asSlice(MemoryAddress, long)

• asSlice

  default MemorySegment asSlice(MemoryAddress newBase, long newSize)

  Obtains a new memory segment view whose base address is the given address, and whose new size is specified by the given argument.

  Equivalent to the following code:

  
      asSlice(newBase.segmentOffset(this), newSize);
   

  Parameters:

  newBase - The new segment base address.

  newSize - The new segment size, specified in bytes.

  Returns:

  a new memory segment view with updated base/limit addresses.

  Throws:

  IndexOutOfBoundsException - if offset < 0, offset > byteSize(), newSize < 0, or newSize > byteSize() - offset

  See Also:

  • asSlice(long)
  • asSlice(MemoryAddress)
  • asSlice(long, long)

• asSlice

  default MemorySegment asSlice(long offset)

  Obtains a new memory segment view whose base address is the same as the base address of this segment plus a given offset, and whose new size is computed by subtracting the specified offset from this segment size.

  Equivalent to the following code:

  
      asSlice(offset, byteSize() - offset);
   

  Parameters:

  offset - The new segment base offset (relative to the current segment base address), specified in bytes.

  Returns:

  a new memory segment view with updated base/limit addresses.

  Throws:

  IndexOutOfBoundsException - if offset < 0, or offset > byteSize().

  See Also:

  • asSlice(MemoryAddress)
  • asSlice(MemoryAddress, long)
  • asSlice(long, long)

• asSlice

  default MemorySegment asSlice(MemoryAddress newBase)

  Obtains a new memory segment view whose base address is the given address, and whose new size is computed by subtracting the address offset relative to this segment (see MemoryAddress.segmentOffset(MemorySegment)) from this segment size.

  Equivalent to the following code:

  
      asSlice(newBase.segmentOffset(this));
   

  Parameters:

  newBase - The new segment base offset (relative to the current segment base address), specified in bytes.

  Returns:

  a new memory segment view with updated base/limit addresses.

  Throws:

  IndexOutOfBoundsException - if address.segmentOffset(this) < 0, or address.segmentOffset(this) > byteSize().

  See Also:

  • asSlice(long)
  • asSlice(MemoryAddress, long)
  • asSlice(long, long)

• isReadOnly

  boolean isReadOnly()

  Is this segment read-only?

  Returns:

  true, if this segment is read-only.

  See Also:

  • asReadOnly()

• asReadOnly

  MemorySegment asReadOnly()

  Obtains a read-only view of this segment. The resulting segment will be identical to this one, but attempts to overwrite the contents of the returned segment will cause runtime exceptions.

  Returns:

  a read-only view of this segment

  See Also:

  • isReadOnly()

• isNative

  boolean isNative()

  Is this a native segment? Returns true if this segment is a native memory segment, created using the allocateNative(long, ResourceScope) (and related) factory, or a buffer segment derived from a direct ByteBuffer using the ofByteBuffer(ByteBuffer) factory, or if this is a mapped segment.

  Returns:

  true if this segment is native segment.

• isMapped

  boolean isMapped()

  Is this a mapped segment? Returns true if this segment is a mapped memory segment, created using the mapFile(Path, long, long, FileChannel.MapMode, ResourceScope) factory, or a buffer segment derived from a MappedByteBuffer using the ofByteBuffer(ByteBuffer) factory.

  Returns:

  true if this segment is a mapped segment.

• fill

  MemorySegment fill(byte value)

  Fills a value into this memory segment.

  More specifically, the given value is filled into each address of this segment. Equivalent to (but likely more efficient than) the following code:

  
  byteHandle = MemoryLayout.ofSequence(MemoryLayouts.JAVA_BYTE)
           .varHandle(byte.class, MemoryLayout.PathElement.sequenceElement());
  for (long l = 0; l < segment.byteSize(); l++) {
       byteHandle.set(segment.address(), l, value);
  }
   

  without any regard or guarantees on the ordering of particular memory elements being set.

  Fill can be useful to initialize or reset the memory of a segment.

  Parameters:

  value - the value to fill into this segment

  Returns:

  this memory segment

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope,

  UnsupportedOperationException - if this segment is read-only (see isReadOnly()).

• copyFrom

  void copyFrom(MemorySegment src)

  Performs a bulk copy from given source segment to this segment. More specifically, the bytes at offset 0 through src.byteSize() - 1 in the source segment are copied into this segment at offset 0 through src.byteSize() - 1. If the source segment overlaps with this segment, then the copying is performed as if the bytes at offset 0 through src.byteSize() - 1 in the source segment were first copied into a temporary segment with size bytes, and then the contents of the temporary segment were copied into this segment at offset 0 through src.byteSize() - 1.

  The result of a bulk copy is unspecified if, in the uncommon case, the source segment and this segment do not overlap, but refer to overlapping regions of the same backing storage using different addresses. For example, this may occur if the same file is mapped to two segments.

  Parameters:

  src - the source segment.

  Throws:

  IndexOutOfBoundsException - if src.byteSize() > this.byteSize().

  IllegalStateException - if either the scope associated with the source segment or the scope associated with this segment have been already closed, or if access occurs from a thread other than the thread owning either scopes.

  UnsupportedOperationException - if this segment is read-only (see isReadOnly()).

• mismatch

  long mismatch(MemorySegment other)

  Finds and returns the offset, in bytes, of the first mismatch between this segment and a given other segment. The offset is relative to the base address of each segment and will be in the range of 0 (inclusive) up to the size (in bytes) of the smaller memory segment (exclusive).

  If the two segments share a common prefix then the returned offset is the length of the common prefix and it follows that there is a mismatch between the two segments at that offset within the respective segments. If one segment is a proper prefix of the other then the returned offset is the smaller of the segment sizes, and it follows that the offset is only valid for the larger segment. Otherwise, there is no mismatch and -1 is returned.

  Parameters:

  other - the segment to be tested for a mismatch with this segment

  Returns:

  the relative offset, in bytes, of the first mismatch between this and the given other segment, otherwise -1 if no mismatch

  Throws:

  IllegalStateException - if either the scope associated with this segment or the scope associated with the other segment have been already closed, or if access occurs from a thread other than the thread owning either scopes.

• isLoaded

  boolean isLoaded()

  Tells whether or not the contents of this mapped segment is resident in physical memory.

  A return value of true implies that it is highly likely that all of the data in this segment is resident in physical memory and may therefore be accessed without incurring any virtual-memory page faults or I/O operations. A return value of false does not necessarily imply that this segment's content is not resident in physical memory.

  The returned value is a hint, rather than a guarantee, because the underlying operating system may have paged out some of this segment's data by the time that an invocation of this method returns.

  Returns:

  true if it is likely that the contents of this segment is resident in physical memory

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope.

  UnsupportedOperationException - if this segment is not a mapped memory segment, e.g. if isMapped() == false.

• load

  void load()

  Loads the contents of this mapped segment into physical memory.

  This method makes a best effort to ensure that, when it returns, this contents of this segment is resident in physical memory. Invoking this method may cause some number of page faults and I/O operations to occur.

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope.

  UnsupportedOperationException - if this segment is not a mapped memory segment, e.g. if isMapped() == false.

• unload

  void unload()

  Unloads the contents of this mapped segment from physical memory.

  This method makes a best effort to ensure that the contents of this segment are are no longer resident in physical memory. Accessing this segment's contents after invoking this method may cause some number of page faults and I/O operations to occur (as this segment's contents might need to be paged back in).

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope.

  UnsupportedOperationException - if this segment is not a mapped memory segment, e.g. if isMapped() == false.

• force

  void force()

  Forces any changes made to the contents of this mapped segment to be written to the storage device described by the mapped segment's file descriptor.

  If the file descriptor associated with this mapped segment resides on a local storage device then when this method returns it is guaranteed that all changes made to this segment since it was created, or since this method was last invoked, will have been written to that device.

  If the file descriptor associated with this mapped segment does not reside on a local device then no such guarantee is made.

  If this segment was not mapped in read/write mode (FileChannel.MapMode.READ_WRITE) then invoking this method may have no effect. In particular, the method has no effect for segments mapped in read-only or private mapping modes. This method may or may not have an effect for implementation-specific mapping modes.

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope.

  UnsupportedOperationException - if this segment is not a mapped memory segment, e.g. if isMapped() == false.

  UncheckedIOException - if there is an I/O error writing the contents of this segment to the associated storage device

• asByteBuffer

  ByteBuffer asByteBuffer()

  Wraps this segment in a ByteBuffer. Some of the properties of the returned buffer are linked to the properties of this segment. For instance, if this segment is immutable (e.g. the segment is a read-only segment, see isReadOnly()), then the resulting buffer is read-only (see Buffer.isReadOnly(). Additionally, if this is a native memory segment, the resulting buffer is direct (see ByteBuffer.isDirect()).

  The returned buffer's position (see Buffer.position() is initially set to zero, while the returned buffer's capacity and limit (see Buffer.capacity() and Buffer.limit(), respectively) are set to this segment' size (see byteSize()). For this reason, a byte buffer cannot be returned if this segment' size is greater than Integer.MAX_VALUE.

  The life-cycle of the returned buffer will be tied to that of this segment. That is, accessing the returned buffer after the scope associated with this segment has been closed (see ResourceScope.close(), will throw an IllegalStateException.

  If this segment is associated with a confined scope, calling read/write I/O operations on the resulting buffer might result in an unspecified exception being thrown. Examples of such problematic operations are AsynchronousSocketChannel.read(ByteBuffer) and AsynchronousSocketChannel.write(ByteBuffer).

  Finally, the resulting buffer's byte order is ByteOrder.BIG_ENDIAN; this can be changed using ByteBuffer.order(java.nio.ByteOrder).

  Returns:

  a ByteBuffer view of this memory segment.

  Throws:

  UnsupportedOperationException - if this segment cannot be mapped onto a ByteBuffer instance, e.g. because it models an heap-based segment that is not based on a byte[]), or if its size is greater than Integer.MAX_VALUE.

• toByteArray

  byte[] toByteArray()

  Copy the contents of this memory segment into a fresh byte array.

  Returns:

  a fresh byte array copy of this memory segment.

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope, or if this segment's contents cannot be copied into a byte instance, e.g. its size is greater than Integer.MAX_VALUE.

• toShortArray

  short[] toShortArray()

  Copy the contents of this memory segment into a fresh short array.

  Returns:

  a fresh short array copy of this memory segment.

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope, or if this segment's contents cannot be copied into a short instance, e.g. because byteSize() % 2 != 0, or byteSize() / 2 > Integer#MAX_VALUE

• toCharArray

  char[] toCharArray()

  Copy the contents of this memory segment into a fresh char array.

  Returns:

  a fresh char array copy of this memory segment.

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope, or if this segment's contents cannot be copied into a char instance, e.g. because byteSize() % 2 != 0, or byteSize() / 2 > Integer#MAX_VALUE.

• toIntArray

  int[] toIntArray()

  Copy the contents of this memory segment into a fresh int array.

  Returns:

  a fresh int array copy of this memory segment.

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope, or if this segment's contents cannot be copied into a int instance, e.g. because byteSize() % 4 != 0, or byteSize() / 4 > Integer#MAX_VALUE.

• toFloatArray

  float[] toFloatArray()

  Copy the contents of this memory segment into a fresh float array.

  Returns:

  a fresh float array copy of this memory segment.

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope, or if this segment's contents cannot be copied into a float instance, e.g. because byteSize() % 4 != 0, or byteSize() / 4 > Integer#MAX_VALUE.

• toLongArray

  long[] toLongArray()

  Copy the contents of this memory segment into a fresh long array.

  Returns:

  a fresh long array copy of this memory segment.

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope, or if this segment's contents cannot be copied into a long instance, e.g. because byteSize() % 8 != 0, or byteSize() / 8 > Integer#MAX_VALUE.

• toDoubleArray

  double[] toDoubleArray()

  Copy the contents of this memory segment into a fresh double array.

  Returns:

  a fresh double array copy of this memory segment.

  Throws:

  IllegalStateException - if the scope associated with this segment has been closed, or if access occurs from a thread other than the thread owning that scope, or if this segment's contents cannot be copied into a double instance, e.g. because byteSize() % 8 != 0, or byteSize() / 8 > Integer#MAX_VALUE.

• ofByteBuffer

  static MemorySegment ofByteBuffer(ByteBuffer bb)

  Creates a new confined buffer memory segment that models the memory associated with the given byte buffer. The segment starts relative to the buffer's position (inclusive) and ends relative to the buffer's limit (exclusive).

  If the buffer is read-only, the resulting segment will also be read-only. The scope associated with this segment can either be the global resource scope, in case the buffer has been created independently, or to some other (possibly closeable) resource scope, in case the buffer has been obtained using asByteBuffer().

  The resulting memory segment keeps a reference to the backing buffer, keeping it reachable.

  Parameters:

  bb - the byte buffer backing the buffer memory segment.

  Returns:

  a new buffer memory segment.

• ofArray

  static MemorySegment ofArray(byte[] arr)

  Creates a new confined array memory segment that models the memory associated with a given heap-allocated byte array. The returned segment's resource scope is set to the global resource scope.

  Parameters:

  arr - the primitive array backing the array memory segment.

  Returns:

  a new array memory segment.

• ofArray

  static MemorySegment ofArray(char[] arr)

  Creates a new confined array memory segment that models the memory associated with a given heap-allocated char array. The returned segment's resource scope is set to the global resource scope.

  Parameters:

  arr - the primitive array backing the array memory segment.

  Returns:

  a new array memory segment.

• ofArray

  static MemorySegment ofArray(short[] arr)

  Creates a new confined array memory segment that models the memory associated with a given heap-allocated short array. The returned segment's resource scope is set to the global resource scope.

  Parameters:

  arr - the primitive array backing the array memory segment.

  Returns:

  a new array memory segment.

• ofArray

  static MemorySegment ofArray(int[] arr)

  Creates a new confined array memory segment that models the memory associated with a given heap-allocated int array. The returned segment's resource scope is set to the global resource scope.

  Parameters:

  arr - the primitive array backing the array memory segment.

  Returns:

  a new array memory segment.

• ofArray

  static MemorySegment ofArray(float[] arr)

  Creates a new confined array memory segment that models the memory associated with a given heap-allocated float array. The returned segment's resource scope is set to the global resource scope.

  Parameters:

  arr - the primitive array backing the array memory segment.

  Returns:

  a new array memory segment.

• ofArray

  static MemorySegment ofArray(long[] arr)

  Creates a new confined array memory segment that models the memory associated with a given heap-allocated long array. The returned segment's resource scope is set to the global resource scope.

  Parameters:

  arr - the primitive array backing the array memory segment.

  Returns:

  a new array memory segment.

• ofArray

  static MemorySegment ofArray(double[] arr)

  Creates a new confined array memory segment that models the memory associated with a given heap-allocated double array. The returned segment's resource scope is set to the global resource scope.

  Parameters:

  arr - the primitive array backing the array memory segment.

  Returns:

  a new array memory segment.

• allocateNative

  static MemorySegment allocateNative(MemoryLayout layout, ResourceScope scope)

  Creates a new confined native memory segment that models a newly allocated block of off-heap memory with given layout and resource scope. A client is responsible make sure that the resource scope associated with the returned segment is closed when the segment is no longer in use. Failure to do so will result in off-heap memory leaks.

  This is equivalent to the following code:

  
      allocateNative(layout.bytesSize(), layout.bytesAlignment(), scope);
   

  The block of off-heap memory associated with the returned native memory segment is initialized to zero.

  Parameters:

  layout - the layout of the off-heap memory block backing the native memory segment.

  scope - the segment scope.

  Returns:

  a new native memory segment.

  Throws:

  IllegalArgumentException - if the specified layout has illegal size or alignment constraint.

  IllegalStateException - if scope has been already closed, or if access occurs from a thread other than the thread owning scope.

• allocateNative

  static MemorySegment allocateNative(long bytesSize, ResourceScope scope)

  Creates a new confined native memory segment that models a newly allocated block of off-heap memory with given size (in bytes) and resource scope. A client is responsible make sure that the resource scope associated with the returned segment is closed when the segment is no longer in use. Failure to do so will result in off-heap memory leaks.

  This is equivalent to the following code:

  
      allocateNative(bytesSize, 1, scope);
   

  The block of off-heap memory associated with the returned native memory segment is initialized to zero.

  Parameters:

  bytesSize - the size (in bytes) of the off-heap memory block backing the native memory segment.

  scope - the segment scope.

  Returns:

  a new native memory segment.

  Throws:

  IllegalArgumentException - if bytesSize <= 0.

  IllegalStateException - if scope has been already closed, or if access occurs from a thread other than the thread owning scope.

• allocateNative

  static MemorySegment allocateNative(long bytesSize, long alignmentBytes, ResourceScope scope)

  Creates a new confined native memory segment that models a newly allocated block of off-heap memory with given size (in bytes), alignment constraint (in bytes) and resource scope. A client is responsible make sure that the resource scope associated with the returned segment is closed when the segment is no longer in use. Failure to do so will result in off-heap memory leaks.

  The block of off-heap memory associated with the returned native memory segment is initialized to zero.

  Parameters:

  bytesSize - the size (in bytes) of the off-heap memory block backing the native memory segment.

  alignmentBytes - the alignment constraint (in bytes) of the off-heap memory block backing the native memory segment.

  scope - the segment scope.

  Returns:

  a new native memory segment.

  Throws:

  IllegalArgumentException - if bytesSize <= 0, alignmentBytes <= 0, or if alignmentBytes is not a power of 2.

  IllegalStateException - if scope has been already closed, or if access occurs from a thread other than the thread owning scope.

• mapFile

  static MemorySegment mapFile(Path path, long bytesOffset, long bytesSize, FileChannel.MapMode mapMode, ResourceScope scope) throws IOException

  Creates a new mapped memory segment that models a memory-mapped region of a file from a given path.

  If the specified mapping mode is READ_ONLY, the resulting segment will be read-only (see isReadOnly()).

  The content of a mapped memory segment can change at any time, for example if the content of the corresponding region of the mapped file is changed by this (or another) program. Whether or not such changes occur, and when they occur, is operating-system dependent and therefore unspecified.

  All or part of a mapped memory segment may become inaccessible at any time, for example if the backing mapped file is truncated. An attempt to access an inaccessible region of a mapped memory segment will not change the segment's content and will cause an unspecified exception to be thrown either at the time of the access or at some later time. It is therefore strongly recommended that appropriate precautions be taken to avoid the manipulation of a mapped file by this (or another) program, except to read or write the file's content.

  Implementation Note:

  When obtaining a mapped segment from a newly created file, the initialization state of the contents of the block of mapped memory associated with the returned mapped memory segment is unspecified and should not be relied upon.

  Parameters:

  path - the path to the file to memory map.

  bytesOffset - the offset (expressed in bytes) within the file at which the mapped segment is to start.

  bytesSize - the size (in bytes) of the mapped memory backing the memory segment.

  mapMode - a file mapping mode, see FileChannel.map(FileChannel.MapMode, long, long); the chosen mapping mode might affect the behavior of the returned memory mapped segment (see force()).

  scope - the segment scope.

  Returns:

  a new confined mapped memory segment.

  Throws:

  IllegalArgumentException - if bytesOffset < 0, bytesSize < 0, or if path is not associated with the default file system.

  IllegalStateException - if scope has been already closed, or if access occurs from a thread other than the thread owning scope.

  UnsupportedOperationException - if an unsupported map mode is specified.

  IOException - if the specified path does not point to an existing file, or if some other I/O error occurs.

  SecurityException - If a security manager is installed and it denies an unspecified permission required by the implementation. In the case of the default provider, the SecurityManager.checkRead(String) method is invoked to check read access if the file is opened for reading. The SecurityManager.checkWrite(String) method is invoked to check write access if the file is opened for writing.

• globalNativeSegment

  static MemorySegment globalNativeSegment()

  Returns a native memory segment whose base address is MemoryAddress.NULL and whose size is Long.MAX_VALUE. This method can be very useful when dereferencing memory addresses obtained when interacting with native libraries. The returned segment is associated with the global resource scope (see ResourceScope.globalScope()). Equivalent to (but likely more efficient than) the following code:

  
      MemoryAddress.NULL.asSegment(Long.MAX_VALUE)
   

  This method is restricted. Restricted methods are unsafe, and, if used incorrectly, their use might crash the JVM or, worse, silently result in memory corruption. Thus, clients should refrain from depending on restricted methods, and use safe and supported functionalities, where possible.

  Returns:

  a memory segment whose base address is MemoryAddress.NULL and whose size is Long.MAX_VALUE.

  Throws:

  IllegalCallerException - if access to this method occurs from a module M and the command line option --enable-native-access is either absent, or does not mention the module name M, or ALL-UNNAMED in case M is an unnamed module.