From 121e43c2b7500d40f1ae1889e5cdbe9ec3a9baa4 Mon Sep 17 00:00:00 2001
From: Soutaro Matsumoto <matsumoto@soutaro.com>
Date: Tue, 24 Dec 2024 15:46:10 +0900
Subject: [PATCH] Add `Ractor.store_if_absent`

---
 core/ractor.rbs | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/core/ractor.rbs b/core/ractor.rbs
index 48b0dfd02..731e835a2 100644
--- a/core/ractor.rbs
+++ b/core/ractor.rbs
@@ -588,6 +588,23 @@ class Ractor
   #
   def self.shareable?: (untyped obj) -> bool
 
+  # <!--
+  #   rdoc-file=ractor.rb
+  #   - Ractor.store_if_absent(key){ init_block }
+  # -->
+  # If the correponding value is not set, yield a value with init_block and store
+  # the value in thread-safe manner. This method returns corresponding stored
+  # value.
+  #
+  #     (1..10).map{
+  #       Thread.new(it){|i|
+  #         Ractor.store_if_absent(:s){ f(); i }
+  #         #=> return stored value of key :s
+  #       }
+  #     }.map(&:value).uniq.size #=> 1 and f() is called only once
+  #
+  def self.store_if_absent: (Symbol) { () -> untyped } -> untyped
+
   # <!--
   #   rdoc-file=ractor.rb
   #   - Ractor.yield(msg, move: false) -> nil