[ruby/fiddle] Add Fiddle::Closure.create and Fiddle::Closure.free

GitHub: fix GH-102

It's for freeing a closure explicitly.

We can't use Fiddle::Closure before we fork the process. If we do it,
the process may be crashed with SELinux.

See https://github.com/ruby/fiddle/issues/102#issuecomment-1241763091
for details.

Reported by Vít Ondruch. Thanks!!!

https://github.com/ruby/fiddle/commit/a0ccc6bb1b

ext/fiddle/closure.c

@@ -224,6 +224,17 @@ allocate(VALUE klass)
     return i;
 }
 
+static fiddle_closure *
+get_raw(VALUE self)
+{
+    fiddle_closure *closure;
+    TypedData_Get_Struct(self, fiddle_closure, &closure_data_type, closure);
+    if (!closure) {
+        rb_raise(rb_eArgError, "already freed: %+"PRIsVALUE, self);
+    }
+    return closure;
+}
+
 static VALUE
 initialize(int rbargc, VALUE argv[], VALUE self)
 {
@@ -293,14 +304,28 @@ initialize(int rbargc, VALUE argv[], VALUE self)
 static VALUE
 to_i(VALUE self)
 {
-    fiddle_closure * cl;
-    void *code;
+    fiddle_closure *closure = get_raw(self);
+    return PTR2NUM(closure->code);
+}
 
-    TypedData_Get_Struct(self, fiddle_closure, &closure_data_type, cl);
+static VALUE
+closure_free(VALUE self)
+{
+    fiddle_closure *closure;
+    TypedData_Get_Struct(self, fiddle_closure, &closure_data_type, closure);
+    if (closure) {
+        dealloc(closure);
+        RTYPEDDATA_DATA(self) = NULL;
+    }
+    return RUBY_Qnil;
+}
 
-    code = cl->code;
-
-    return PTR2NUM(code);
+static VALUE
+closure_freed_p(VALUE self)
+{
+    fiddle_closure *closure;
+    TypedData_Get_Struct(self, fiddle_closure, &closure_data_type, closure);
+    return closure ? RUBY_Qfalse : RUBY_Qtrue;
 }
 
 void
@@ -353,8 +378,24 @@ Init_fiddle_closure(void)
     /*
      * Document-method: to_i
      *
-     * Returns the memory address for this closure
+     * Returns the memory address for this closure.
      */
     rb_define_method(cFiddleClosure, "to_i", to_i, 0);
+
+    /*
+     * Document-method: free
+     *
+     * Free this closure explicitly. You can't use this closure anymore.
+     *
+     * If this closure is already freed, this does nothing.
+     */
+    rb_define_method(cFiddleClosure, "free", closure_free, 0);
+
+    /*
+     * Document-method: freed?
+     *
+     * Whether this closure was freed explicitly.
+     */
+    rb_define_method(cFiddleClosure, "freed?", closure_freed_p, 0);
 }
 /* vim: set noet sw=4 sts=4 */

ext/fiddle/lib/fiddle/closure.rb

@@ -1,6 +1,31 @@
 # frozen_string_literal: true
 module Fiddle
   class Closure
+    class << self
+      # Create a new closure. If a block is given, the created closure
+      # is automatically freed after the given block is executed.
+      #
+      # The all given arguments are passed to Fiddle::Closure.new. So
+      # using this method without block equals to Fiddle::Closure.new.
+      #
+      # == Example
+      #
+      #   Fiddle::Closure.create(TYPE_INT, [TYPE_INT]) do |closure|
+      #     # closure is freed automatically when this block is finished.
+      #   end
+      def create(*args)
+        if block_given?
+          closure = new(*args)
+          begin
+            yield(closure)
+          ensure
+            closure.free
+          end
+        else
+          new(*args)
+        end
+      end
+    end
 
     # the C type of the return of the FFI closure
     attr_reader :ctype

test/fiddle/test_closure.rb

@@ -29,37 +29,40 @@ module Fiddle
     end
 
     def test_type_symbol
-      closure = Closure.new(:int, [:void])
-      assert_equal([
-                     TYPE_INT,
-                     [TYPE_VOID],
-                   ],
-                   [
-                     closure.instance_variable_get(:@ctype),
-                     closure.instance_variable_get(:@args),
-                   ])
+      Closure.create(:int, [:void]) do |closure|
+        assert_equal([
+                       TYPE_INT,
+                       [TYPE_VOID],
+                     ],
+                     [
+                       closure.instance_variable_get(:@ctype),
+                       closure.instance_variable_get(:@args),
+                     ])
+      end
     end
 
     def test_call
-      closure = Class.new(Closure) {
+      closure_class = Class.new(Closure) do
         def call
           10
         end
-      }.new(TYPE_INT, [])
-
-      func = Function.new(closure, [], TYPE_INT)
-      assert_equal 10, func.call
+      end
+      closure_class.create(TYPE_INT, []) do |closure|
+        func = Function.new(closure, [], TYPE_INT)
+        assert_equal 10, func.call
+      end
     end
 
     def test_returner
-      closure = Class.new(Closure) {
+      closure_class = Class.new(Closure) do
         def call thing
           thing
         end
-      }.new(TYPE_INT, [TYPE_INT])
-
-      func = Function.new(closure, [TYPE_INT], TYPE_INT)
-      assert_equal 10, func.call(10)
+      end
+      closure_class.create(TYPE_INT, [TYPE_INT]) do |closure|
+        func = Function.new(closure, [TYPE_INT], TYPE_INT)
+        assert_equal 10, func.call(10)
+      end
     end
 
     def test_const_string
@@ -69,18 +72,35 @@ module Fiddle
           @return_string
         end
       end
-      closure = closure_class.new(:const_string, [:const_string])
+      closure_class.create(:const_string, [:const_string]) do |closure|
+        func = Function.new(closure, [:const_string], :const_string)
+        assert_equal("Hello! World!", func.call("World!"))
+      end
+    end
 
-      func = Function.new(closure, [:const_string], :const_string)
-      assert_equal("Hello! World!", func.call("World!"))
+    def test_free
+      Closure.create(:int, [:void]) do |closure|
+        assert do
+          not closure.freed?
+        end
+        closure.free
+        assert do
+          closure.freed?
+        end
+        closure.free
+      end
     end
 
     def test_block_caller
       cb = Closure::BlockCaller.new(TYPE_INT, [TYPE_INT]) do |one|
         one
       end
-      func = Function.new(cb, [TYPE_INT], TYPE_INT)
-      assert_equal 11, func.call(11)
+      begin
+        func = Function.new(cb, [TYPE_INT], TYPE_INT)
+        assert_equal 11, func.call(11)
+      ensure
+        cb.free
+      end
     end
 
     def test_memsize
@@ -97,23 +117,21 @@ module Fiddle
         define_method("test_conversion_#{n.downcase}") do
           arg = nil
 
-          clos = Class.new(Closure) do
+          closure_class = Class.new(Closure) do
             define_method(:call) {|x| arg = x}
-          end.new(t, [t])
+          end
+          closure_class.create(t, [t]) do |closure|
+            v = ~(~0 << (8*s))
 
-          v = ~(~0 << (8*s))
+            arg = nil
+            assert_equal(v, closure.call(v))
+            assert_equal(arg, v, n)
 
-          arg = nil
-          assert_equal(v, clos.call(v))
-          assert_equal(arg, v, n)
-
-          arg = nil
-          func = Function.new(clos, [t], t)
-          assert_equal(v, func.call(v))
-          assert_equal(arg, v, n)
-        ensure
-          clos = nil
-          func = nil
+            arg = nil
+            func = Function.new(closure, [t], t)
+            assert_equal(v, func.call(v))
+            assert_equal(arg, v, n)
+          end
         end
       end
     end