Freeze results that come from the database

Freeze strings and row records so that we can more easily share results
among Ractors

ext/sqlite3/statement.c

@@ -162,13 +162,15 @@ step(VALUE self)
                         if (internal_encoding) {
                             val = rb_str_export_to_enc(val, internal_encoding);
                         }
+                        rb_obj_freeze(val);
                     }
                     break;
                     case SQLITE_BLOB: {
                         val = rb_str_new(
                                   (const char *)sqlite3_column_blob(stmt, i),
                                   (long)sqlite3_column_bytes(stmt, i)
                               );
+                        rb_obj_freeze(val);
                     }
                     break;
                     case SQLITE_NULL:
@@ -192,6 +194,8 @@ step(VALUE self)
             CHECK(sqlite3_db_handle(ctx->st), value);
     }
 
+    rb_obj_freeze(list);
+
     return list;
 }
 

lib/sqlite3/database.rb

@@ -208,7 +208,7 @@ def execute sql, bind_vars = [], *args, &block
             yield row
           end
         else
-          stmt.to_a
+          stmt.to_a.freeze
         end
       end
     end

test/test_encoding.rb

@@ -82,7 +82,7 @@ def test_blob_is_binary
 
       string = @db.execute("select data from foo").first.first
       assert_equal Encoding.find("ASCII-8BIT"), string.encoding
-      assert_equal str, string.force_encoding("UTF-8")
+      assert_equal str, string.dup.force_encoding("UTF-8")
     end
 
     def test_blob_is_ascii8bit
@@ -95,7 +95,7 @@ def test_blob_is_ascii8bit
 
       string = @db.execute("select data from foo").first.first
       assert_equal Encoding.find("ASCII-8BIT"), string.encoding
-      assert_equal str, string.force_encoding("UTF-8")
+      assert_equal str, string.dup.force_encoding("UTF-8")
     end
 
     def test_blob_with_eucjp
@@ -108,7 +108,7 @@ def test_blob_with_eucjp
 
       string = @db.execute("select data from foo").first.first
       assert_equal Encoding.find("ASCII-8BIT"), string.encoding
-      assert_equal str, string.force_encoding("EUC-JP")
+      assert_equal str, string.dup.force_encoding("EUC-JP")
     end
 
     def test_db_with_eucjp

test/test_statement.rb

@@ -12,6 +12,23 @@ def teardown
       @db.close
     end
 
+    def test_rows_should_be_frozen
+      @db.execute 'CREATE TABLE "things" ("float" float, "int" int, "text" blob, "string" string, "nil" string)'
+      stmt = @db.prepare "INSERT INTO things (float, int, text, string, nil) VALUES (?, ?, ?, ?, ?)"
+      stmt.execute(1.2, 2, "blob", "string", nil)
+      stmt.close
+
+      rows = @db.execute "SELECT float, int, text, string, nil FROM things"
+      assert_predicate rows, :frozen?
+      assert_equal 1, rows.length
+      row = rows[0]
+      assert_predicate row, :frozen?
+      row.each { |item| assert_predicate item, :frozen? }
+
+      assert Ractor.shareable?(rows)
+      assert Ractor.shareable?(row)
+    end
+
     def test_double_close_does_not_segv
       @db.execute 'CREATE TABLE "things" ("number" float NOT NULL)'