Fix async Python functors invoking from multiple C++ threads (pybind#1587)

uentity · uentity · commit cfab0d39e8a7 · 2018-11-06T09:26:30.000+05:00
Ensure GIL is released after functor destructor finished (not only
during functor execution as in previous implementation).
diff --git a/include/pybind11/functional.h b/include/pybind11/functional.h
@@ -54,9 +54,11 @@ struct type_caster<std::function<Return(Args...)>> {
             }
         }
 
-        value = [func](Args... args) -> Return {
+        value = [func](Args... args) mutable -> Return {
             gil_scoped_acquire acq;
-            object retval(func(std::forward<Args>(args)...));
+            // move into local var to ensure GIL is released AFTER functor destructor is called
+            function f(std::move(func));
+            object retval(f(std::forward<Args>(args)...));
             /* Visual studio 2015 parser issue: need parentheses around this expression */
             return (retval.template cast<Return>());
         };

Original file line number	Diff line number	Diff line change
`@@ -54,9 +54,11 @@ struct type_caster<std::function<Return(Args...)>> {`
`54`	`54`	`}`
`55`	`55`	`}`
`56`	`56`
`57`		`- value = [func](Args... args) -> Return {`
	`57`	`+ value = [func](Args... args) mutable -> Return {`
`58`	`58`	`gil_scoped_acquire acq;`
`59`		`- object retval(func(std::forward<Args>(args)...));`
	`59`	`+ // move into local var to ensure GIL is released AFTER functor destructor is called`
	`60`	`+ function f(std::move(func));`
	`61`	`+ object retval(f(std::forward<Args>(args)...));`
`60`	`62`	`/* Visual studio 2015 parser issue: need parentheses around this expression */`
`61`	`63`	`return (retval.template cast<Return>());`
`62`	`64`	`};`