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Warn in verbose mode on defining a finalizer that captures the object #2264

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Warn in verbose mode on defining a finalizer that captures the object #2264

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43 changes: 43 additions & 0 deletions gc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2954,6 +2954,42 @@ should_be_finalizable(VALUE obj)
rb_check_frozen(obj);
}

struct should_not_capture_data {
VALUE obj;
VALUE set;
bool found;
};

static void
should_not_capture_callback(const VALUE child, struct should_not_capture_data *data)
{
if (child == data->obj)
data->found = true;

if (data->found)
return;

// Maintain a set of objects already searched, so that we don't follow a cycle
VALUE key = rb_obj_id(child);
if (rb_hash_has_key(data->set, key))
return;
rb_hash_aset(data->set, key, Qtrue);
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Should we just use the object itself as the hash key?

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When we use rb_objspace_reachable_objects_from we get internal objects - RUBY_T_IMEMO and I think specifically instruction sequences. These aren't hashable (don't respond to hash). I'd welcome a suggestion about alternative data structures to use instead of a Hash - could I use the st hash structure directly? Or some kind of identity hash?


rb_objspace_reachable_objects_from(child, (void (*)(unsigned long, void *)) &should_not_capture_callback, (void *)data);
}

static void
should_not_capture(VALUE block, VALUE obj)
{
struct should_not_capture_data data;
data.obj = obj;
data.set = rb_hash_new();
data.found = false;
rb_objspace_reachable_objects_from(block, (void (*)(unsigned long, void *)) &should_not_capture_callback, (void *)&data);
if (data.found)
rb_warn("object is reachable from finalizer - it may never be run");
}

/*
* call-seq:
* ObjectSpace.define_finalizer(obj, aProc=proc())
Expand All @@ -2963,6 +2999,10 @@ should_be_finalizable(VALUE obj)
* as an argument to <i>aProc</i>. If <i>aProc</i> is a lambda or
* method, make sure it can be called with a single argument.
*
* In verbose mode (<code>-w</code>) a warning will be issued if
* the object is reachable from <i>aProc</i>, which may prevent
* finalization.
*
*/

static VALUE
Expand All @@ -2979,6 +3019,9 @@ define_final(int argc, VALUE *argv, VALUE os)
should_be_callable(block);
}

if (ruby_verbose)
should_not_capture(block, obj);

return define_final0(obj, block);
}

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26 changes: 26 additions & 0 deletions spec/ruby/core/objectspace/define_finalizer_spec.rb
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Expand Up @@ -65,4 +65,30 @@ def scoped

ruby_exe(code).lines.sort.should == ["finalized1\n", "finalized2\n"]
end

it "warns in verbose mode if it is self-referencing" do
code = <<-RUBY
obj = "Test"
handler = Proc.new { puts "finalized" }
ObjectSpace.define_finalizer(obj, handler)
exit 0
RUBY

ruby_exe(code, :options => "-w", :args => "2>&1").should include("warning: object is reachable from finalizer - it may never be run")
end

it "warns in verbose mode if it is indirectly self-referencing" do
code = <<-RUBY
def scoped(indirect)
Proc.new { puts "finalized" }
end
obj = "Test"
indirect = [obj]
handler = scoped(indirect)
ObjectSpace.define_finalizer(obj, handler)
exit 0
RUBY

ruby_exe(code, :options => "-w", :args => "2>&1").should include("warning: object is reachable from finalizer - it may never be run")
end
end