Make Digest() thread-safe.

* ext/digest/lib/digest.rb (Digest()): This function should now be
  thread-safe.  If you have a problem with regard to on-demand
  loading under a multi-threaded environment, preload "digest/*"
  modules on boot or use this method instead of directly
  referencing Digest::*. [Bug ruby#9494]
  cf. aws/aws-sdk-ruby#525

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48213 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,12 @@
+Fri Oct 31 22:19:30 2014  Akinori MUSHA  <knu@iDaemons.org>
+
+	* ext/digest/lib/digest.rb (Digest()): This function should now be
+	  thread-safe.  If you have a problem with regard to on-demand
+	  loading under a multi-threaded environment, preload "digest/*"
+	  modules on boot or use this method instead of directly
+	  referencing Digest::*. [Bug #9494]
+	  cf. https://github.com/aws/aws-sdk-ruby/issues/525
+
 Fri Oct 31 21:33:17 2014  Akinori MUSHA  <knu@iDaemons.org>
 
 	* test/digest/test_digest.rb: Drop #!.  This no longer runs

NEWS

@@ -128,6 +128,11 @@ with all sufficient information, see the ChangeLog file.
 === Stdlib updates (outstanding ones only)
 
 * Digest
+
+  * Digest() should now be thread-safe.  If you have a problem with
+    regard to on-demand loading under a multi-threaded environment,
+    preload "digest/*" modules on boot or use this method instead of
+    directly referencing Digest::*.
   * Digest::HMAC has been removed just as previously noticed.
 
 * Etc

ext/digest/lib/digest.rb

@@ -1,6 +1,9 @@
 require 'digest.so'
 
 module Digest
+  # A mutex for Digest().
+  REQUIRE_MUTEX = Mutex.new
+
   def self.const_missing(name) # :nodoc:
     case name
     when :SHA256, :SHA384, :SHA512
@@ -76,15 +79,30 @@ def base64digest!
 # call-seq:
 #   Digest(name) -> digest_subclass
 #
-# Returns a Digest subclass by +name+.
+# Returns a Digest subclass by +name+ in a thread-safe manner even
+# when on-demand loading is involved.
 #
 #   require 'digest'
 #
 #   Digest("MD5")
 #   # => Digest::MD5
 #
-#   Digest("Foo")
+#   Digest(:SHA256)
+#   # => Digest::SHA256
+#
+#   Digest(:Foo)
 #   # => LoadError: library not found for class Digest::Foo -- digest/foo
 def Digest(name)
-  Digest.const_get(name)
+  const = name.to_sym
+  Digest::REQUIRE_MUTEX.synchronize {
+    # Ignore autoload's because it is void when we have #const_missing
+    Digest.const_missing(const)
+  }
+rescue LoadError
+  # Constants do not necessarily rely on digest/*.
+  if Digest.const_defined?(const)
+    Digest.const_get(const)
+  else
+    raise
+  end
 end

test/digest/digest/foo.rb

@@ -0,0 +1,10 @@
+module Digest
+  Foo = nil
+
+  sleep 0.2
+
+  remove_const(:Foo)
+
+  class Foo < Class
+  end
+end

test/digest/test_digest.rb

@@ -208,4 +208,65 @@ def test_initialize_copy_md5_rmd160
       end
     end
   end
+
+  class TestDigestParen < Test::Unit::TestCase
+    def test_sha2
+      assert_separately(%w[-rdigest], <<-'end;')
+        assert_nothing_raised {
+          Digest(:SHA256).new
+          Digest(:SHA384).new
+          Digest(:SHA512).new
+        }
+      end;
+    end
+
+    def test_no_lib
+      assert_separately(%w[-rdigest], <<-'end;')
+        class Digest::Nolib < Digest::Class
+        end
+
+        assert_nothing_raised {
+          Digest(:Nolib).new
+        }
+      end;
+    end
+
+    def test_no_lib_no_def
+      assert_separately(%w[-rdigest], <<-'end;')
+        assert_raise(LoadError) {
+          Digest(:Nodef).new
+        }
+      end;
+    end
+
+    def test_race
+      assert_separately(['-rdigest', "-I#{File.dirname(__FILE__)}"], <<-'end;')
+        assert_nothing_raised {
+          t = Thread.start {
+            sleep 0.1
+            Digest(:Foo).new
+          }
+          Digest(:Foo).new
+          t.join
+        }
+      end;
+    end
+
+    def test_race_mixed
+      assert_separately(['-rdigest', "-I#{File.dirname(__FILE__)}"], <<-'end;')
+        assert_nothing_raised {
+          t = Thread.start {
+            sleep 0.1
+            Digest::Foo.new
+          }
+          Digest(:Foo).new
+          begin
+            t.join
+          rescue NoMethodError, NameError
+            # NoMethodError is highly likely; NameError is listed just in case
+          end
+        }
+      end;
+    end
+  end
 end