fix: match actor selection wildcards without backtracking (#3506) - #3519
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* fix: match actor selection wildcards without backtracking Motivation: SelectChildPattern compiled its glob to a regular expression with Helpers.makePattern, which turns every '*' into '.*'. A chain of those backtracks: the 26 character pattern "*a*a*a*a*a*a*a*a*a*a*a*a*b" matched against a 36 character actor name that cannot satisfy the trailing literal takes about 42 seconds on one thread. An ActorSelectionMessage carries its pattern elements in the message, so that cost is reachable from one small message, and deliverSelection runs on the caller's thread for a local selection and on the inbound stream thread for a remote one. Bounding the pattern length would not help, since 26 characters is already enough. Modification: Add Glob (@internalapi), which matches the same grammar - '?' is one character, '*' is any run, everything else is literal - by remembering only the most recent '*' rather than by backtracking, so it runs in time proportional to the product of the two lengths at worst. Match through it in ActorSelection.deliverSelection. SelectChildPattern.pattern is kept for compatibility but is now lazy, so deserializing a selection no longer compiles a regular expression either. Result: The same selections match as before, in time linear in practice. * scalafmt
pjfanning
requested review from
He-Pin,
Philippus,
nvollmar,
raboof and
samueleresca
September 4, 2026 09:45
nvollmar
approved these changes
Sep 4, 2026
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Motivation
Backport of #3506 to 1.7.x: wildcard actor-selection matching went through a regular
expression that backtracks badly — a 26-character pattern in an
ActorSelectionMessagecould pin the inbound stream thread for tens of seconds.
Modification
Cherry-pick of ec62931. The only conflict was the import line in
ActorSelection.scala(1.7.x also imports
JavaDurationConverters,ccompatandFutureConvertersthere);resolved by adding
Globto the existing import.Glob.scalaandGlobSpecappliedclean — they are plain Scala 2 syntax and Java 8 APIs throughout.
Result
Same as #3506: the same selections match as before, in time linear in practice, and
deserializing a selection no longer compiles a regular expression.
Tests
sbt "++ 2.12.21 actor-tests/Test/compile"— clean, validating Scala 2.12sbt "actor/scalafmtCheckAll" "actor-tests/scalafmtCheckAll"— cleanfrom fix: match actor selection wildcards without backtracking #3506, including the exhaustive agreement check against
Helpers.makePatternReferences
Backport of #3506.