Package org.antlr.v4.runtime.atn

Class RetainedConfigSet

java.lang.Object

org.antlr.v4.runtime.atn.RetainedConfigSet

final class RetainedConfigSet
extends Object

Lazily allocated, capacity-preserving scratch ATNConfigSet for prediction and lexing hot paths.

Ownership contract (single rule): obtain(int) always returns an empty writable set (clears on reuse). Callers must release() in a finally after the edge / closure work so config-graph references are dropped between uses while list/map capacity is retained. DFA storage must clone before release().

PERF: Both obtain(int) and release() may call ATNConfigSet.clear(). That clear is intentionally cheap when the buffer is already empty (no full-table Arrays.fill on the merge map) and only nulls the used list prefix when non-empty — see ATNConfigSet.clear() and ClearableLongObjectHashMap. The obtain/release pair therefore does not pay double bulk-zero of the open- addressed tables on the common path (release empties; obtain is a free empty clear). Skipping clear on obtain entirely would leave flags/storage dirty if a caller reused without release; both sides stay defensive.

Package-private: shared by ParserATNSimulator, LexerATNSimulator, and tests in this package.

Field Summary

Fields

Modifier and Type	Field	Description
private ATNConfigSet	buffer
private final boolean	ordered

Constructor Summary

Constructors

Constructor	Description
RetainedConfigSet(boolean ordered)

Method Summary

Modifier and Type	Method	Description
(package private) ATNConfigSet	buffer()	Underlying buffer after first obtain(int), else null.
(package private) ATNConfigSet	obtain(int sourceSize)	Returns the retained buffer, allocating on first use.
(package private) void	release()	Drops config-graph references held by the buffer; keeps capacity.

Methods inherited from class java.lang.Object

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

Field Details

ordered

private final boolean ordered

buffer

@Nullable
private ATNConfigSet buffer

Constructor Details

RetainedConfigSet

RetainedConfigSet(boolean ordered)

Parameters:

ordered - true for OrderedATNConfigSet (lexer), false for plain ATNConfigSet (parser)

Method Details

obtain

@NotNull
ATNConfigSet obtain(int sourceSize)

Returns the retained buffer, allocating on first use. Always empty on return (clears when reusing an existing buffer). Clear of an already-empty buffer is O(1) for the merge map (see ATNConfigSet.clear()).

Parameters:

sourceSize - hint for initial capacity (ATNConfigSet.scratchCapacity(int))

release

void release()

Drops config-graph references held by the buffer; keeps capacity. No-op if obtain(int) has never been called. When the buffer is already empty, clear is O(1) for the merge map and does not bulk-zero backing arrays.

buffer

@Nullable
ATNConfigSet buffer()

Underlying buffer after first obtain(int), else null. Same-package tests may observe identity and emptiness.