uk.ac.starlink.table

Class ProgressRowSplittable

java.lang.Object

uk.ac.starlink.table.ProgressRowSplittable

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable, RowData, RowSequence, RowSplittable, Sequence, Splittable<RowSplittable>

public class ProgressRowSplittable
extends java.lang.Object
implements RowSplittable

RowSplittable wrapper that can manage progress reporting, as well as force termination of iteration.

Note that it is important to close instances of this splittable for correct progress reporting.

Since:

12 Oct 2020

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	ProgressRowSplittable.Target Callback interface for objects that will be informed about iteration progress, and also given the opportunity to terminate iteration.

Constructor Summary

Constructors

Constructor and Description
ProgressRowSplittable(RowSplittable base, ProgressRowSplittable.Target target) Public constructor.

Method Summary

Modifier and Type	Method and Description
void	close() Indicates that this sequence will not be required any more.
java.lang.Object	getCell(int icol) Returns the contents of a cell in the current row.
java.lang.Object[]	getRow() Returns the contents of the current table row, as an array with the same number of elements as there are columns in this table.
boolean	next() Attempts to advance the current row to the next one.
java.util.function.LongSupplier	rowIndex() Returns a supplier for the index of the row currently being processed, if possible.
ProgressRowSplittable	split() Attempts to partition this object into two halves, ideally of similar size.
long	splittableSize() Provides an estimate of the number of processable items in this object.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ProgressRowSplittable

public ProgressRowSplittable(RowSplittable base,
                             ProgressRowSplittable.Target target)

Public constructor.

Parameters:

base - splittable which this one is to monitor

target - object to which progress events are reported

Method Detail

next

public boolean next()
             throws java.io.IOException

Description copied from interface: RowSequence

Attempts to advance the current row to the next one. If true is returned the attempt has been successful, and if false is returned there are no more rows in this sequence. Since the initial position of a RowSequence is before the first row, this method must be called before current row data can be accessed using the RowSequence.getCell(int) or RowSequence.getRow() methods.

Specified by:

next in interface RowSequence

Specified by:

next in interface Sequence

Returns:

true iff this sequence has been advanced to the next row

Throws:

java.io.IOException - if there is some error

split

public ProgressRowSplittable split()

Description copied from interface: Splittable

Attempts to partition this object into two halves, ideally of similar size. If a non-null value is returned, then the content previously contained by this object is now split between this object and the returned object. If for any reason a split is not carried out, null is returned.

Following a successful call, the two parts may be processed in different threads.

Specified by:

split in interface Splittable<RowSplittable>

Returns:

other half of this splittable, or null

See Also:

Spliterator.trySplit()

getCell

public java.lang.Object getCell(int icol)
                         throws java.io.IOException

Description copied from interface: RowSequence

Returns the contents of a cell in the current row. The class of the returned object should be the same as, or a subclass of, the class returned by getColumnInfo(icol).getContentClass(). An unchecked exception will be thrown if there is no current row (next has not yet been called).

Specified by:

getCell in interface RowData

Specified by:

getCell in interface RowSequence

Parameters:

icol - column index

Returns:

the contents of cell icol in the current row

Throws:

java.io.IOException - if there is an error reading the data

getRow

public java.lang.Object[] getRow()
                          throws java.io.IOException

Description copied from interface: RowSequence

Returns the contents of the current table row, as an array with the same number of elements as there are columns in this table. An unchecked exception will be thrown if there is no current row (next has not yet been called).

Specified by:

getRow in interface RowData

Specified by:

getRow in interface RowSequence

Returns:

an array of the objects in each cell in row irow

Throws:

java.io.IOException - if there is an error reading the data

rowIndex

public java.util.function.LongSupplier rowIndex()

Description copied from interface: RowSplittable

Returns a supplier for the index of the row currently being processed, if possible. The row index is a global value; when accessing the first row of a top-level RowSplittable, the value returned by this supplier should be the first index in the table. But for objects resulting from splitting a top-level instance into sub-instances, the return value should reflect the index in the original sequence of rows; each index should be returned from only one of the splittables resulting from splitting a top-level instance.

Typically, the row index will start at 0 and increment for each row, but the numbering may be different depending on the requirements of the implementation or usage.

Before the RowSequence.next() method has been called, the return value will be one less than the first row index. After RowSequence.next has returned false, the value is undefined.

Depending on the implementation, it may not be possible to determine the row index (for instance if the sequence is split into sub-splittables of unknown size). In such cases, this method returns null. The null-ness of the return value must be the same for all instances of the splittable hierarchy for a given sequence, so don't return a non-null value for the first splittable and then null values for some or all of its children.

Specified by:

rowIndex in interface RowSplittable

Returns:

supplier for the globally-referenced row index value of the current row of this sequence, or null

splittableSize

public long splittableSize()

Description copied from interface: Splittable

Provides an estimate of the number of processable items in this object. A processable item is not a well-defined quantity, but it should generally be something that can be processed fast. For instance, if this object represents a collection of collections, the value that should be returned is the total number of elements rather than the number of collections.

If no estimate for the size is available, a negative value should be returned.

Specified by:

splittableSize in interface Splittable<RowSplittable>

Returns:

approximate size, or negative value if not known

close

public void close()
           throws java.io.IOException

Description copied from interface: RowSequence

Indicates that this sequence will not be required any more. This should release resources associated with this object. The effect of calling any of the other methods following a close is undefined.

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface RowSequence

Throws:

java.io.IOException