8029452: Fork/Join task ForEachOps.ForEachOrderedTask clarifications and minor improvements
Reviewed-by: mduigou, briangoetz
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package java.util.stream;
import java.util.EnumMap;
import java.util.Map;
import java.util.Spliterator;
/**
* Flags corresponding to characteristics of streams and operations. Flags are
* utilized by the stream framework to control, specialize or optimize
* computation.
*
* <p>
* Stream flags may be used to describe characteristics of several different
* entities associated with streams: stream sources, intermediate operations,
* and terminal operations. Not all stream flags are meaningful for all
* entities; the following table summarizes which flags are meaningful in what
* contexts:
*
* <div>
* <table>
* <caption>Type Characteristics</caption>
* <thead class="tableSubHeadingColor">
* <tr>
* <th colspan="2"> </th>
* <th>{@code DISTINCT}</th>
* <th>{@code SORTED}</th>
* <th>{@code ORDERED}</th>
* <th>{@code SIZED}</th>
* <th>{@code SHORT_CIRCUIT}</th>
* </tr>
* </thead>
* <tbody>
* <tr>
* <th colspan="2" class="tableSubHeadingColor">Stream source</th>
* <td>Y</td>
* <td>Y</td>
* <td>Y</td>
* <td>Y</td>
* <td>N</td>
* </tr>
* <tr>
* <th colspan="2" class="tableSubHeadingColor">Intermediate operation</th>
* <td>PCI</td>
* <td>PCI</td>
* <td>PCI</td>
* <td>PC</td>
* <td>PI</td>
* </tr>
* <tr>
* <th colspan="2" class="tableSubHeadingColor">Terminal operation</th>
* <td>N</td>
* <td>N</td>
* <td>PC</td>
* <td>N</td>
* <td>PI</td>
* </tr>
* </tbody>
* <tfoot>
* <tr>
* <th class="tableSubHeadingColor" colspan="2">Legend</th>
* <th colspan="6" rowspan="7"> </th>
* </tr>
* <tr>
* <th class="tableSubHeadingColor">Flag</th>
* <th class="tableSubHeadingColor">Meaning</th>
* <th colspan="6"></th>
* </tr>
* <tr><td>Y</td><td>Allowed</td></tr>
* <tr><td>N</td><td>Invalid</td></tr>
* <tr><td>P</td><td>Preserves</td></tr>
* <tr><td>C</td><td>Clears</td></tr>
* <tr><td>I</td><td>Injects</td></tr>
* </tfoot>
* </table>
* </div>
*
* <p>In the above table, "PCI" means "may preserve, clear, or inject"; "PC"
* means "may preserve or clear", "PI" means "may preserve or inject", and "N"
* means "not valid".
*
* <p>Stream flags are represented by unioned bit sets, so that a single word
* may describe all the characteristics of a given stream entity, and that, for
* example, the flags for a stream source can be efficiently combined with the
* flags for later operations on that stream.
*
* <p>The bit masks {@link #STREAM_MASK}, {@link #OP_MASK}, and
* {@link #TERMINAL_OP_MASK} can be ANDed with a bit set of stream flags to
* produce a mask containing only the valid flags for that entity type.
*
* <p>When describing a stream source, one only need describe what
* characteristics that stream has; when describing a stream operation, one need
* describe whether the operation preserves, injects, or clears that
* characteristic. Accordingly, two bits are used for each flag, so as to allow
* representing not only the presence of of a characteristic, but how an
* operation modifies that characteristic. There are two common forms in which
* flag bits are combined into an {@code int} bit set. <em>Stream flags</em>
* are a unioned bit set constructed by ORing the enum characteristic values of
* {@link #set()} (or, more commonly, ORing the corresponding static named
* constants prefixed with {@code IS_}). <em>Operation flags</em> are a unioned
* bit set constructed by ORing the enum characteristic values of {@link #set()}
* or {@link #clear()} (to inject, or clear, respectively, the corresponding
* flag), or more commonly ORing the corresponding named constants prefixed with
* {@code IS_} or {@code NOT_}. Flags that are not marked with {@code IS_} or
* {@code NOT_} are implicitly treated as preserved. Care must be taken when
* combining bitsets that the correct combining operations are applied in the
* correct order.
*
* <p>
* With the exception of {@link #SHORT_CIRCUIT}, stream characteristics can be
* derived from the equivalent {@link java.util.Spliterator} characteristics:
* {@link java.util.Spliterator#DISTINCT}, {@link java.util.Spliterator#SORTED},
* {@link java.util.Spliterator#ORDERED}, and
* {@link java.util.Spliterator#SIZED}. A spliterator characteristics bit set
* can be converted to stream flags using the method
* {@link #fromCharacteristics(java.util.Spliterator)} and converted back using
* {@link #toCharacteristics(int)}. (The bit set
* {@link #SPLITERATOR_CHARACTERISTICS_MASK} is used to AND with a bit set to
* produce a valid spliterator characteristics bit set that can be converted to
* stream flags.)
*
* <p>
* The source of a stream encapsulates a spliterator. The characteristics of
* that source spliterator when transformed to stream flags will be a proper
* subset of stream flags of that stream.
* For example:
* <pre> {@code
* Spliterator s = ...;
* Stream stream = Streams.stream(s);
* flagsFromSplitr = fromCharacteristics(s.characteristics());
* assert(flagsFromSplitr & stream.getStreamFlags() == flagsFromSplitr);
* }</pre>
*
* <p>
* An intermediate operation, performed on an input stream to create a new
* output stream, may preserve, clear or inject stream or operation
* characteristics. Similarly, a terminal operation, performed on an input
* stream to produce an output result may preserve, clear or inject stream or
* operation characteristics. Preservation means that if that characteristic
* is present on the input, then it is also present on the output. Clearing
* means that the characteristic is not present on the output regardless of the
* input. Injection means that the characteristic is present on the output
* regardless of the input. If a characteristic is not cleared or injected then
* it is implicitly preserved.
*
* <p>
* A pipeline consists of a stream source encapsulating a spliterator, one or
* more intermediate operations, and finally a terminal operation that produces
* a result. At each stage of the pipeline, a combined stream and operation
* flags can be calculated, using {@link #combineOpFlags(int, int)}. Such flags
* ensure that preservation, clearing and injecting information is retained at
* each stage.
*
* The combined stream and operation flags for the source stage of the pipeline
* is calculated as follows:
* <pre> {@code
* int flagsForSourceStage = combineOpFlags(sourceFlags, INITIAL_OPS_VALUE);
* }</pre>
*
* The combined stream and operation flags of each subsequent intermediate
* operation stage in the pipeline is calculated as follows:
* <pre> {@code
* int flagsForThisStage = combineOpFlags(flagsForPreviousStage, thisOpFlags);
* }</pre>
*
* Finally the flags output from the last intermediate operation of the pipeline
* are combined with the operation flags of the terminal operation to produce
* the flags output from the pipeline.
*
* <p>Those flags can then be used to apply optimizations. For example, if
* {@code SIZED.isKnown(flags)} returns true then the stream size remains
* constant throughout the pipeline, this information can be utilized to
* pre-allocate data structures and combined with
* {@link java.util.Spliterator#SUBSIZED} that information can be utilized to
* perform concurrent in-place updates into a shared array.
*
* For specific details see the {@link AbstractPipeline} constructors.
*
* @since 1.8
*/
enum StreamOpFlag {
/*
* Each characteristic takes up 2 bits in a bit set to accommodate
* preserving, clearing and setting/injecting information.
*
* This applies to stream flags, intermediate/terminal operation flags, and
* combined stream and operation flags. Even though the former only requires
* 1 bit of information per characteristic, is it more efficient when
* combining flags to align set and inject bits.
*
* Characteristics belong to certain types, see the Type enum. Bit masks for
* the types are constructed as per the following table:
*
* DISTINCT SORTED ORDERED SIZED SHORT_CIRCUIT
* SPLITERATOR 01 01 01 01 00
* STREAM 01 01 01 01 00
* OP 11 11 11 10 01
* TERMINAL_OP 00 00 10 00 01
* UPSTREAM_TERMINAL_OP 00 00 10 00 00
*
* 01 = set/inject
* 10 = clear
* 11 = preserve
*
* Construction of the columns is performed using a simple builder for
* non-zero values.
*/
// The following flags correspond to characteristics on Spliterator
// and the values MUST be equal.
//
/**
* Characteristic value signifying that, for each pair of
* encountered elements in a stream {@code x, y}, {@code !x.equals(y)}.
* <p>
* A stream may have this value or an intermediate operation can preserve,
* clear or inject this value.
*/
// 0, 0x00000001
// Matches Spliterator.DISTINCT
DISTINCT(0,
set(Type.SPLITERATOR).set(Type.STREAM).setAndClear(Type.OP)),
/**
* Characteristic value signifying that encounter order follows a natural
* sort order of comparable elements.
* <p>
* A stream can have this value or an intermediate operation can preserve,
* clear or inject this value.
* <p>
* Note: The {@link java.util.Spliterator#SORTED} characteristic can define
* a sort order with an associated non-null comparator. Augmenting flag
* state with addition properties such that those properties can be passed
* to operations requires some disruptive changes for a singular use-case.
* Furthermore, comparing comparators for equality beyond that of identity
* is likely to be unreliable. Therefore the {@code SORTED} characteristic
* for a defined non-natural sort order is not mapped internally to the
* {@code SORTED} flag.
*/
// 1, 0x00000004
// Matches Spliterator.SORTED
SORTED(1,
set(Type.SPLITERATOR).set(Type.STREAM).setAndClear(Type.OP)),
/**
* Characteristic value signifying that an encounter order is
* defined for stream elements.
* <p>
* A stream can have this value, an intermediate operation can preserve,
* clear or inject this value, or a terminal operation can preserve or clear
* this value.
*/
// 2, 0x00000010
// Matches Spliterator.ORDERED
ORDERED(2,
set(Type.SPLITERATOR).set(Type.STREAM).setAndClear(Type.OP).clear(Type.TERMINAL_OP)
.clear(Type.UPSTREAM_TERMINAL_OP)),
/**
* Characteristic value signifying that size of the stream
* is of a known finite size that is equal to the known finite
* size of the source spliterator input to the first stream
* in the pipeline.
* <p>
* A stream can have this value or an intermediate operation can preserve or
* clear this value.
*/
// 3, 0x00000040
// Matches Spliterator.SIZED
SIZED(3,
set(Type.SPLITERATOR).set(Type.STREAM).clear(Type.OP)),
// The following Spliterator characteristics are not currently used but a
// gap in the bit set is deliberately retained to enable corresponding
// stream flags if//when required without modification to other flag values.
//
// 4, 0x00000100 NONNULL(4, ...
// 5, 0x00000400 IMMUTABLE(5, ...
// 6, 0x00001000 CONCURRENT(6, ...
// 7, 0x00004000 SUBSIZED(7, ...
// The following 4 flags are currently undefined and a free for any further
// spliterator characteristics.
//
// 8, 0x00010000
// 9, 0x00040000
// 10, 0x00100000
// 11, 0x00400000
// The following flags are specific to streams and operations
//
/**
* Characteristic value signifying that an operation may short-circuit the
* stream.
* <p>
* An intermediate operation can preserve or inject this value,
* or a terminal operation can preserve or inject this value.
*/
// 12, 0x01000000
SHORT_CIRCUIT(12,
set(Type.OP).set(Type.TERMINAL_OP));
// The following 2 flags are currently undefined and a free for any further
// stream flags if/when required
//
// 13, 0x04000000
// 14, 0x10000000
// 15, 0x40000000
/**
* Type of a flag
*/
enum Type {
/**
* The flag is associated with spliterator characteristics.
*/
SPLITERATOR,
/**
* The flag is associated with stream flags.
*/
STREAM,
/**
* The flag is associated with intermediate operation flags.
*/
OP,
/**
* The flag is associated with terminal operation flags.
*/
TERMINAL_OP,
/**
* The flag is associated with terminal operation flags that are
* propagated upstream across the last stateful operation boundary
*/
UPSTREAM_TERMINAL_OP
}
/**
* The bit pattern for setting/injecting a flag.
*/
private static final int SET_BITS = 0b01;
/**
* The bit pattern for clearing a flag.
*/
private static final int CLEAR_BITS = 0b10;
/**
* The bit pattern for preserving a flag.
*/
private static final int PRESERVE_BITS = 0b11;
private static MaskBuilder set(Type t) {
return new MaskBuilder(new EnumMap<>(Type.class)).set(t);
}
private static class MaskBuilder {
final Map<Type, Integer> map;
MaskBuilder(Map<Type, Integer> map) {
this.map = map;
}
MaskBuilder mask(Type t, Integer i) {
map.put(t, i);
return this;
}
MaskBuilder set(Type t) {
return mask(t, SET_BITS);
}
MaskBuilder clear(Type t) {
return mask(t, CLEAR_BITS);
}
MaskBuilder setAndClear(Type t) {
return mask(t, PRESERVE_BITS);
}
Map<Type, Integer> build() {
for (Type t : Type.values()) {
map.putIfAbsent(t, 0b00);
}
return map;
}
}
/**
* The mask table for a flag, this is used to determine if a flag
* corresponds to a certain flag type and for creating mask constants.
*/
private final Map<Type, Integer> maskTable;
/**
* The bit position in the bit mask.
*/
private final int bitPosition;
/**
* The set 2 bit set offset at the bit position.
*/
private final int set;
/**
* The clear 2 bit set offset at the bit position.
*/
private final int clear;
/**
* The preserve 2 bit set offset at the bit position.
*/
private final int preserve;
private StreamOpFlag(int position, MaskBuilder maskBuilder) {
this.maskTable = maskBuilder.build();
// Two bits per flag
position *= 2;
this.bitPosition = position;
this.set = SET_BITS << position;
this.clear = CLEAR_BITS << position;
this.preserve = PRESERVE_BITS << position;
}
/**
* Gets the bitmap associated with setting this characteristic.
*
* @return the bitmap for setting this characteristic
*/
int set() {
return set;
}
/**
* Gets the bitmap associated with clearing this characteristic.
*
* @return the bitmap for clearing this characteristic
*/
int clear() {
return clear;
}
/**
* Determines if this flag is a stream-based flag.
*
* @return true if a stream-based flag, otherwise false.
*/
boolean isStreamFlag() {
return maskTable.get(Type.STREAM) > 0;
}
/**
* Checks if this flag is set on stream flags, injected on operation flags,
* and injected on combined stream and operation flags.
*
* @param flags the stream flags, operation flags, or combined stream and
* operation flags
* @return true if this flag is known, otherwise false.
*/
boolean isKnown(int flags) {
return (flags & preserve) == set;
}
/**
* Checks if this flag is cleared on operation flags or combined stream and
* operation flags.
*
* @param flags the operation flags or combined stream and operations flags.
* @return true if this flag is preserved, otherwise false.
*/
boolean isCleared(int flags) {
return (flags & preserve) == clear;
}
/**
* Checks if this flag is preserved on combined stream and operation flags.
*
* @param flags the combined stream and operations flags.
* @return true if this flag is preserved, otherwise false.
*/
boolean isPreserved(int flags) {
return (flags & preserve) == preserve;
}
/**
* Determines if this flag can be set for a flag type.
*
* @param t the flag type.
* @return true if this flag can be set for the flag type, otherwise false.
*/
boolean canSet(Type t) {
return (maskTable.get(t) & SET_BITS) > 0;
}
/**
* The bit mask for spliterator characteristics
*/
static final int SPLITERATOR_CHARACTERISTICS_MASK = createMask(Type.SPLITERATOR);
/**
* The bit mask for source stream flags.
*/
static final int STREAM_MASK = createMask(Type.STREAM);
/**
* The bit mask for intermediate operation flags.
*/
static final int OP_MASK = createMask(Type.OP);
/**
* The bit mask for terminal operation flags.
*/
static final int TERMINAL_OP_MASK = createMask(Type.TERMINAL_OP);
/**
* The bit mask for upstream terminal operation flags.
*/
static final int UPSTREAM_TERMINAL_OP_MASK = createMask(Type.UPSTREAM_TERMINAL_OP);
private static int createMask(Type t) {
int mask = 0;
for (StreamOpFlag flag : StreamOpFlag.values()) {
mask |= flag.maskTable.get(t) << flag.bitPosition;
}
return mask;
}
/**
* Complete flag mask.
*/
private static final int FLAG_MASK = createFlagMask();
private static int createFlagMask() {
int mask = 0;
for (StreamOpFlag flag : StreamOpFlag.values()) {
mask |= flag.preserve;
}
return mask;
}
/**
* Flag mask for stream flags that are set.
*/
private static final int FLAG_MASK_IS = STREAM_MASK;
/**
* Flag mask for stream flags that are cleared.
*/
private static final int FLAG_MASK_NOT = STREAM_MASK << 1;
/**
* The initial value to be combined with the stream flags of the first
* stream in the pipeline.
*/
static final int INITIAL_OPS_VALUE = FLAG_MASK_IS | FLAG_MASK_NOT;
/**
* The bit value to set or inject {@link #DISTINCT}.
*/
static final int IS_DISTINCT = DISTINCT.set;
/**
* The bit value to clear {@link #DISTINCT}.
*/
static final int NOT_DISTINCT = DISTINCT.clear;
/**
* The bit value to set or inject {@link #SORTED}.
*/
static final int IS_SORTED = SORTED.set;
/**
* The bit value to clear {@link #SORTED}.
*/
static final int NOT_SORTED = SORTED.clear;
/**
* The bit value to set or inject {@link #ORDERED}.
*/
static final int IS_ORDERED = ORDERED.set;
/**
* The bit value to clear {@link #ORDERED}.
*/
static final int NOT_ORDERED = ORDERED.clear;
/**
* The bit value to set {@link #SIZED}.
*/
static final int IS_SIZED = SIZED.set;
/**
* The bit value to clear {@link #SIZED}.
*/
static final int NOT_SIZED = SIZED.clear;
/**
* The bit value to inject {@link #SHORT_CIRCUIT}.
*/
static final int IS_SHORT_CIRCUIT = SHORT_CIRCUIT.set;
private static int getMask(int flags) {
return (flags == 0)
? FLAG_MASK
: ~(flags | ((FLAG_MASK_IS & flags) << 1) | ((FLAG_MASK_NOT & flags) >> 1));
}
/**
* Combines stream or operation flags with previously combined stream and
* operation flags to produce updated combined stream and operation flags.
* <p>
* A flag set on stream flags or injected on operation flags,
* and injected combined stream and operation flags,
* will be injected on the updated combined stream and operation flags.
*
* <p>
* A flag set on stream flags or injected on operation flags,
* and cleared on the combined stream and operation flags,
* will be cleared on the updated combined stream and operation flags.
*
* <p>
* A flag set on the stream flags or injected on operation flags,
* and preserved on the combined stream and operation flags,
* will be injected on the updated combined stream and operation flags.
*
* <p>
* A flag not set on the stream flags or cleared/preserved on operation
* flags, and injected on the combined stream and operation flags,
* will be injected on the updated combined stream and operation flags.
*
* <p>
* A flag not set on the stream flags or cleared/preserved on operation
* flags, and cleared on the combined stream and operation flags,
* will be cleared on the updated combined stream and operation flags.
*
* <p>
* A flag not set on the stream flags,
* and preserved on the combined stream and operation flags
* will be preserved on the updated combined stream and operation flags.
*
* <p>
* A flag cleared on operation flags,
* and preserved on the combined stream and operation flags
* will be cleared on the updated combined stream and operation flags.
*
* <p>
* A flag preserved on operation flags,
* and preserved on the combined stream and operation flags
* will be preserved on the updated combined stream and operation flags.
*
* @param newStreamOrOpFlags the stream or operation flags.
* @param prevCombOpFlags previously combined stream and operation flags.
* The value {#link INITIAL_OPS_VALUE} must be used as the seed value.
* @return the updated combined stream and operation flags.
*/
static int combineOpFlags(int newStreamOrOpFlags, int prevCombOpFlags) {
// 0x01 or 0x10 nibbles are transformed to 0x11
// 0x00 nibbles remain unchanged
// Then all the bits are flipped
// Then the result is logically or'ed with the operation flags.
return (prevCombOpFlags & StreamOpFlag.getMask(newStreamOrOpFlags)) | newStreamOrOpFlags;
}
/**
* Converts combined stream and operation flags to stream flags.
*
* <p>Each flag injected on the combined stream and operation flags will be
* set on the stream flags.
*
* @param combOpFlags the combined stream and operation flags.
* @return the stream flags.
*/
static int toStreamFlags(int combOpFlags) {
// By flipping the nibbles 0x11 become 0x00 and 0x01 become 0x10
// Shift left 1 to restore set flags and mask off anything other than the set flags
return ((~combOpFlags) >> 1) & FLAG_MASK_IS & combOpFlags;
}
/**
* Converts stream flags to a spliterator characteristic bit set.
*
* @param streamFlags the stream flags.
* @return the spliterator characteristic bit set.
*/
static int toCharacteristics(int streamFlags) {
return streamFlags & SPLITERATOR_CHARACTERISTICS_MASK;
}
/**
* Converts a spliterator characteristic bit set to stream flags.
*
* @implSpec
* If the spliterator is naturally {@code SORTED} (the associated
* {@code Comparator} is {@code null}) then the characteristic is converted
* to the {@link #SORTED} flag, otherwise the characteristic is not
* converted.
*
* @param spliterator the spliterator from which to obtain characteristic
* bit set.
* @return the stream flags.
*/
static int fromCharacteristics(Spliterator<?> spliterator) {
int characteristics = spliterator.characteristics();
if ((characteristics & Spliterator.SORTED) != 0 && spliterator.getComparator() != null) {
// Do not propagate the SORTED characteristic if it does not correspond
// to a natural sort order
return characteristics & SPLITERATOR_CHARACTERISTICS_MASK & ~Spliterator.SORTED;
}
else {
return characteristics & SPLITERATOR_CHARACTERISTICS_MASK;
}
}
/**
* Converts a spliterator characteristic bit set to stream flags.
*
* @param characteristics the spliterator characteristic bit set.
* @return the stream flags.
*/
static int fromCharacteristics(int characteristics) {
return characteristics & SPLITERATOR_CHARACTERISTICS_MASK;
}
}