Package org.antlr.v4.runtime.atn

Class PredictionContextCache

java.lang.Object

org.antlr.v4.runtime.atn.PredictionContextCache

public class PredictionContextCache
extends Object

Used to cache PredictionContext objects. It is used for the shared context cache associated with contexts in DFA states. This cache can be used for both lexers and parsers.

Cache instances created with PredictionContextCache() are intended for single-threaded use during a prediction operation. Concurrent access from multiple threads is not supported (the shared UNCACHED instance is safe because caching is disabled and no mutable probe state is retained).

PERF: getChild(org.antlr.v4.runtime.atn.PredictionContext, int) and join(org.antlr.v4.runtime.atn.PredictionContext, org.antlr.v4.runtime.atn.PredictionContext) use mutable probe keys for map lookups so a cache hit does not allocate a key object. Permanent keys are allocated only on a cache miss when the entry is stored. Probe types are distinct from permanent key types so a probe can never be inserted into the map: the maps are typed as Map<PredictionContextAndInt, …> and Map<IdentityCommutativePredictionContextOperands, …>, while Map.get(Object) still accepts probes because equality is defined on the shared ChildKey/JoinKey bases.

join(org.antlr.v4.runtime.atn.PredictionContext, org.antlr.v4.runtime.atn.PredictionContext) may re-enter itself recursively via PredictionContext.join(org.antlr.v4.runtime.atn.PredictionContext, org.antlr.v4.runtime.atn.PredictionContext); the probe key is only used for the duration of each individual map lookup, and map insertions always use freshly allocated immutable keys.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
(package private) static class	PredictionContextCache.ChildKey	Shared equality/hash contract for (PredictionContext, int) keys used by getChild(org.antlr.v4.runtime.atn.PredictionContext, int).
private static final class	PredictionContextCache.ChildKeyProbe	Mutable probe for getChild(org.antlr.v4.runtime.atn.PredictionContext, int) lookups.
protected static final class	PredictionContextCache.IdentityCommutativePredictionContextOperands	Immutable identity-based commutative key for a pair of PredictionContext instances.
(package private) static class	PredictionContextCache.JoinKey	Shared equality/hash contract for identity-based commutative pairs of PredictionContext used by join(org.antlr.v4.runtime.atn.PredictionContext, org.antlr.v4.runtime.atn.PredictionContext) and by ArrayPredictionContext equality.
private static final class	PredictionContextCache.JoinKeyProbe	Mutable probe for join(org.antlr.v4.runtime.atn.PredictionContext, org.antlr.v4.runtime.atn.PredictionContext) lookups.
protected static final class	PredictionContextCache.PredictionContextAndInt	Immutable map key for (PredictionContext, int) stored in childContexts.

Field Summary

Fields

Modifier and Type	Field	Description
private final Map<PredictionContextCache.PredictionContextAndInt,PredictionContext>	childContexts
private final PredictionContextCache.ChildKeyProbe	childProbe	Reusable probe for getChild(org.antlr.v4.runtime.atn.PredictionContext, int).
private final Map<PredictionContext,PredictionContext>	contexts
private final boolean	enableCache
private final Map<PredictionContextCache.IdentityCommutativePredictionContextOperands,PredictionContext>	joinContexts
private final PredictionContextCache.JoinKeyProbe	joinProbe	Reusable probe for join(org.antlr.v4.runtime.atn.PredictionContext, org.antlr.v4.runtime.atn.PredictionContext).
static final PredictionContextCache	UNCACHED

Constructor Summary

Constructors

Modifier	Constructor	Description
	PredictionContextCache()
private	PredictionContextCache(boolean enableCache)

Method Summary

Modifier and Type	Method	Description
(package private) final void	clear()	Drops every cached entry so this instance can be retained across predictions on a single simulator thread.
PredictionContext	getAsCached(PredictionContext context)
PredictionContext	getChild(PredictionContext context, int invokingState)
(package private) final boolean	isEnableCache()	Returns whether this cache stores contexts.
PredictionContext	join(PredictionContext x, PredictionContext y)

Methods inherited from class java.lang.Object

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

Field Details

UNCACHED

public static final PredictionContextCache UNCACHED

childContexts

private final Map<PredictionContextCache.PredictionContextAndInt,PredictionContext> childContexts

joinContexts

private final Map<PredictionContextCache.IdentityCommutativePredictionContextOperands,PredictionContext> joinContexts

contexts

private final Map<PredictionContext,PredictionContext> contexts

childProbe

private final PredictionContextCache.ChildKeyProbe childProbe

Reusable probe for getChild(org.antlr.v4.runtime.atn.PredictionContext, int). Never passed to Map.put(K, V).

joinProbe

private final PredictionContextCache.JoinKeyProbe joinProbe

Reusable probe for join(org.antlr.v4.runtime.atn.PredictionContext, org.antlr.v4.runtime.atn.PredictionContext). Never passed to Map.put(K, V).

enableCache

private final boolean enableCache

Constructor Details

PredictionContextCache

public PredictionContextCache()

PredictionContextCache

private PredictionContextCache(boolean enableCache)

Method Details

isEnableCache

final boolean isEnableCache()

Returns whether this cache stores contexts. The shared UNCACHED instance always returns false.

Package-private: production code branches on UNCACHED identity or simply calls the cache methods; tests may inspect this flag.

getAsCached

public PredictionContext getAsCached(PredictionContext context)

clear

final void clear()

Drops every cached entry so this instance can be retained across predictions on a single simulator thread. No-op for UNCACHED.

Package-private: only the ATN simulators recycle a retained cache.

getChild

public PredictionContext getChild(PredictionContext context,
 int invokingState)

join

public PredictionContext join(PredictionContext x,
 PredictionContext y)