From 59a72538b6aa26a5fcfa09b213097d74f5f567c8 Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@ruby-lang.org>
Date: Mon, 16 Feb 2026 12:37:18 +0900
Subject: [ruby/pstore] Define the platform constant

Rather than overwriting the predicate method dynamically.

Fix [Bug #21880](https://bugs.ruby-lang.org/issues/21880).

https://github.com/ruby/pstore/commit/b2e474e619
---
 lib/pstore.rb       | 17 +++++------------
 test/test_pstore.rb | 10 ++++++++++
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/lib/pstore.rb b/lib/pstore.rb
index 8f17c11d7d..1ec776e504 100644
--- a/lib/pstore.rb
+++ b/lib/pstore.rb
@@ -667,23 +667,16 @@ class PStore
     end
   end
 
-  def on_windows?
-    is_windows = RUBY_PLATFORM =~ /mswin|mingw|bccwin|wince/
-
-    on_windows_proc = Proc.new do
-      is_windows
-    end
-    Ractor.make_shareable(on_windows_proc) if defined?(Ractor)
-    self.class.__send__(:define_method, :on_windows?, &on_windows_proc) 
-    is_windows
-  end
+  ON_WINDOWS = true & (/mswin|mingw|bccwin|wince/ =~ RUBY_PLATFORM) # :nodoc:
+  private_constant :ON_WINDOWS
 
   def save_data(original_checksum, original_file_size, file)
     new_data = dump(@table)
 
     if new_data.bytesize != original_file_size || CHECKSUM_ALGO.digest(new_data) != original_checksum
-      if @ultra_safe && !on_windows?
-        # Windows doesn't support atomic file renames.
+      if @ultra_safe && !ON_WINDOWS
+        # Once a file is locked, Windows does not guarantee that the
+        # lock will be released until the file is closed.
         save_data_with_atomic_file_rename_strategy(new_data, file)
       else
         save_data_with_fast_strategy(new_data, file)
diff --git a/test/test_pstore.rb b/test/test_pstore.rb
index 696660bd0f..4a65e4fec9 100644
--- a/test/test_pstore.rb
+++ b/test/test_pstore.rb
@@ -66,6 +66,16 @@ class PStoreTest < Test::Unit::TestCase
     end
   end
 
+  def test_data_should_be_stored_correctly_when_in_ultra_safe_mode
+    @pstore.ultra_safe = true
+    @pstore.transaction do
+      @pstore[:foo] = "bar"
+    end
+    @pstore.transaction(true) do
+      assert_equal "bar", @pstore[:foo]
+    end
+  end
+
   def test_writing_inside_readonly_transaction_raises_error
     assert_raise(PStore::Error) do
       @pstore.transaction(true) do
-- 
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