Package org.antlr.v4.runtime.atn

Class EpsilonClosure

java.lang.Object

org.antlr.v4.runtime.atn.EpsilonClosure

final class EpsilonClosure
extends Object

Epsilon-closure engine for adaptive LL(*) prediction.

Owns the busy set, the predicate vs non-predicate control split, and double-buffered intermediate config sets for breadth-first rule-transition merging. Recursive edge walking stays here so ParserATNSimulator remains orchestration-focused rather than absorbing more allocation policy.

PERF: Intermediate config-set buffers and the closure busy set are retained on this instance. A single ParserATNSimulator (and therefore one EpsilonClosure) is used by one parser thread at a time during adaptivePredict, so reuse is safe. Ownership of cleanup is a single try/finally around each close(org.antlr.v4.runtime.atn.ATNConfigSet, org.antlr.v4.runtime.atn.ATNConfigSet, boolean, boolean, org.antlr.v4.runtime.atn.PredictionContextCache, boolean): drop config-graph references after the call while retaining set capacity for the next prediction.

PERF: The busy set is exposed only as Set<ATNConfig> (see OpenAddressedHashSet) so the protected ParserATNSimulator.closure(ATNConfig, ATNConfigSet, ATNConfigSet, Set, boolean, boolean, PredictionContextCache, int, boolean) SPI stays free of HPPC types. Storage remains an open-addressed HPPC table behind the adapter: right-recursion and EOF* guards avoid java.util.HashMap.Node<K extends Object,V extends Object> allocation on every insert, and the flat key array is reused across predictions. Config iteration on the BFS layers is index-based (ATNConfigSet.get(int)) to avoid Iterator objects on the hot path.

Package-private: only ParserATNSimulator constructs and uses this type. Transition target computation is delegated back to the simulator (ParserATNSimulator.getEpsilonTarget(org.antlr.v4.runtime.atn.ATNConfig, org.antlr.v4.runtime.atn.Transition, boolean, boolean, org.antlr.v4.runtime.atn.PredictionContextCache, boolean)) so semantic-predicate and rule-transition policy remain in one place.

Field Summary

Fields

Modifier and Type	Field	Description
private ATNConfigSet	bufferA	Double-buffer scratch sets for BFS rule-transition layering when collectPredicates is false.
private ATNConfigSet	bufferB
private final Set<ATNConfig>	closureBusy	Retained busy set for right-recursion / EOF* guards.
private final ParserATNSimulator	simulator

Constructor Summary

Constructors

Constructor	Description
EpsilonClosure(ParserATNSimulator simulator)

Method Summary

Modifier and Type	Method	Description
(package private) void	close(ATNConfigSet sourceConfigs, ATNConfigSet configs, boolean collectPredicates, boolean hasMoreContext, PredictionContextCache contextCache, boolean treatEofAsEpsilon)	Compute the epsilon closure of every configuration in sourceConfigs, adding the resulting non-epsilon (or EOF-as-epsilon) configurations to configs.
(package private) void	closeOne(ATNConfig config, ATNConfigSet configs, ATNConfigSet intermediate, Set<ATNConfig> closureBusy, boolean collectPredicates, boolean hasMoreContexts, PredictionContextCache contextCache, int depth, boolean treatEofAsEpsilon)	Recursive helper: walk epsilon edges from config, adding leaf configurations to configs and optionally deferring rule transitions to intermediate for breadth-first processing.
private void	ensureIntermediateBuffers(int intermediateHint)	Ensure both intermediate buffers exist.
(package private) boolean	hasIntermediateBuffers()	Whether intermediate BFS buffers have been allocated.
(package private) ATNConfigSet	retainedBufferA()	Intermediate buffer A after first non-predicate closure, else null.
(package private) ATNConfigSet	retainedBufferB()	Intermediate buffer B after first non-predicate closure, else null.
(package private) Set<ATNConfig>	retainedBusy()	Retained busy set (same instance across close(org.antlr.v4.runtime.atn.ATNConfigSet, org.antlr.v4.runtime.atn.ATNConfigSet, boolean, boolean, org.antlr.v4.runtime.atn.PredictionContextCache, boolean) calls).

Methods inherited from class java.lang.Object

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

Field Details

simulator

@NotNull
private final ParserATNSimulator simulator

closureBusy

private final Set<ATNConfig> closureBusy

Retained busy set for right-recursion / EOF* guards. Cleared in close(org.antlr.v4.runtime.atn.ATNConfigSet, org.antlr.v4.runtime.atn.ATNConfigSet, boolean, boolean, org.antlr.v4.runtime.atn.PredictionContextCache, boolean)'s finally; capacity is preserved across predictions. Same-package tests may observe identity via retainedBusy().

Typed as Set so callers and the protected simulator SPI never see HPPC. The concrete instance is an OpenAddressedHashSet that keys by ATNConfig.hashCode() (cached) and ATNConfig.equals(java.lang.Object).

bufferA

private ATNConfigSet bufferA

Double-buffer scratch sets for BFS rule-transition layering when collectPredicates is false. Allocated lazily on first non-predicate closure and reused thereafter.

bufferB

private ATNConfigSet bufferB

Constructor Details

EpsilonClosure

EpsilonClosure(@NotNull
 ParserATNSimulator simulator)

Method Details

close

void close(@NotNull
 ATNConfigSet sourceConfigs,
 @NotNull
 ATNConfigSet configs,
 boolean collectPredicates,
 boolean hasMoreContext,
 @NotNull
 PredictionContextCache contextCache,
 boolean treatEofAsEpsilon)

Compute the epsilon closure of every configuration in sourceConfigs, adding the resulting non-epsilon (or EOF-as-epsilon) configurations to configs.

When collectPredicates is false (the common path in ParserATNSimulator.computeTargetState(org.antlr.v4.runtime.dfa.DFA, org.antlr.v4.runtime.dfa.DFAState, org.antlr.v4.runtime.ParserRuleContext, int, boolean, org.antlr.v4.runtime.atn.PredictionContextCache)), rule transitions are deferred into an intermediate config set and processed breadth-first so configs that enter the same rule via different edges can merge before the rule body is expanded. Intermediate sets use two retained buffers that swap roles each layer — sourceConfigs is never treated as a reusable buffer. When collectPredicates is true, rule transitions are followed immediately and no intermediate set is written.

ensureIntermediateBuffers

private void ensureIntermediateBuffers(int intermediateHint)

Ensure both intermediate buffers exist. Existing buffers are retained (capacity preserved via ATNConfigSet.clear()); the initial expected-size hint only applies on first allocation.

hasIntermediateBuffers

boolean hasIntermediateBuffers()

Whether intermediate BFS buffers have been allocated. Same-package tests may observe retained-scratch identity.

retainedBusy

@NotNull
Set<ATNConfig> retainedBusy()

Retained busy set (same instance across close(org.antlr.v4.runtime.atn.ATNConfigSet, org.antlr.v4.runtime.atn.ATNConfigSet, boolean, boolean, org.antlr.v4.runtime.atn.PredictionContextCache, boolean) calls). Typed as Set; the concrete implementation is OpenAddressedHashSet.

retainedBufferA

@Nullable
ATNConfigSet retainedBufferA()

Intermediate buffer A after first non-predicate closure, else null.

retainedBufferB

@Nullable
ATNConfigSet retainedBufferB()

Intermediate buffer B after first non-predicate closure, else null.

closeOne

void closeOne(@NotNull
 ATNConfig config,
 @NotNull
 ATNConfigSet configs,
 @Nullable
 ATNConfigSet intermediate,
 @NotNull
 Set<ATNConfig> closureBusy,
 boolean collectPredicates,
 boolean hasMoreContexts,
 @NotNull
 PredictionContextCache contextCache,
 int depth,
 boolean treatEofAsEpsilon)

Recursive helper: walk epsilon edges from config, adding leaf configurations to configs and optionally deferring rule transitions to intermediate for breadth-first processing.

Parameters:

closureBusy - busy set for right-recursion / EOF* guards; production callers pass the retained OpenAddressedHashSet, but any Set is accepted so the protected simulator override SPI stays interface-oriented