[libcxx] func.wrap.func.con: Unset function before destroying anything

Be defensive against a reentrant std::function::operator=(nullptr_t), in case
the held function object has a non-trivial destructor.  Destroying the function
object in-place can lead to the destructor being called twice.

Patch by Duncan P. N. Exon Smith. C++03 support by Volodymyr Sapsai.

rdar://problem/32836603

Reviewers: EricWF, mclow.lists

Reviewed By: mclow.lists

Subscribers: cfe-commits, arphaman

Differential Revision: https://reviews.llvm.org/D34331


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@330885 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/move_reentrant.pass.cpp

@@ -0,0 +1,46 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <functional>
+
+// class function<R(ArgTypes...)>
+
+// function& operator=(function &&);
+
+#include <functional>
+#include <cassert>
+
+#include "test_macros.h"
+
+struct A
+{
+  static std::function<void()> global;
+  static bool cancel;
+
+  ~A() {
+    DoNotOptimize(cancel);
+    if (cancel)
+      global = std::function<void()>(nullptr);
+  }
+  void operator()() {}
+};
+
+std::function<void()> A::global;
+bool A::cancel = false;
+
+int main()
+{
+  A::global = A();
+  assert(A::global.target<A>());
+
+  // Check that we don't recurse in A::~A().
+  A::cancel = true;
+  A::global = std::function<void()>(nullptr);
+  assert(!A::global.target<A>());
+}

test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/nullptr_t_assign_reentrant.pass.cpp

@@ -0,0 +1,46 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <functional>
+
+// class function<R(ArgTypes...)>
+
+// function& operator=(nullptr_t);
+
+#include <functional>
+#include <cassert>
+
+#include "test_macros.h"
+
+struct A
+{
+  static std::function<void()> global;
+  static bool cancel;
+
+  ~A() {
+    DoNotOptimize(cancel);
+    if (cancel)
+      global = nullptr;
+  }
+  void operator()() {}
+};
+
+std::function<void()> A::global;
+bool A::cancel = false;
+
+int main()
+{
+  A::global = A();
+  assert(A::global.target<A>());
+
+  // Check that we don't recurse in A::~A().
+  A::cancel = true;
+  A::global = nullptr;
+  assert(!A::global.target<A>());
+}