libstdc++: Clear std::priority_queue after moving from it [PR118088]

We don't know what state an arbitrary sequence container will be in
after moving from it, so a moved-from std::priority_queue needs to clear
the moved-from container to ensure it doesn't contain elements that are
in an invalid order for the queue. An alternative would be to call
std::make_heap again to re-establish the rvalue queue's invariant, but
that could potentially cause an exception to be thrown. Just clearing it
so the sequence is empty seems safer and more likely to match user
expectations.

libstdc++-v3/ChangeLog:

	PR libstdc++/118088
	* include/bits/stl_queue.h (priority_queue(priority_queue&&)):
	Clear the source object after moving from it.
	(priority_queue(priority_queue&&, const Alloc&)): Likewise.
	(operator=(priority_queue&&)): Likewise.
	* testsuite/23_containers/priority_queue/118088.cc: New test.

Reviewed-by: Patrick Palka <ppalka@redhat.com>

diff --git a/libstdc++-v3/include/bits/stl_queue.h b/libstdc++-v3/include/bits/stl_queue.h
index ada354b911db0fca2776be1fbe7c0cabad103e56..53a9a47a2d2bf128c20c7bed956631153a901a80 100644 (file)
--- a/libstdc++-v3/include/bits/stl_queue.h
+++ b/libstdc++-v3/include/bits/stl_queue.h
@@ -564,6 +564,26 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       : c(std::move(__s)), comp(__x)
       { std::make_heap(c.begin(), c.end(), comp); }
 
+      priority_queue(const priority_queue&) = default;
+      priority_queue& operator=(const priority_queue&) = default;
+
+      priority_queue(priority_queue&& __q)
+      noexcept(__and_<is_nothrow_move_constructible<_Sequence>,
+                     is_nothrow_move_constructible<_Compare>>::value)
+      : c(std::move(__q.c)), comp(std::move(__q.comp))
+      { __q.c.clear(); }
+
+      priority_queue&
+      operator=(priority_queue&& __q)
+      noexcept(__and_<is_nothrow_move_assignable<_Sequence>,
+                     is_nothrow_move_assignable<_Compare>>::value)
+      {
+       c = std::move(__q.c);
+       __q.c.clear();
+       comp = std::move(__q.comp);
+       return *this;
+      }
+
       template<typename _Alloc, typename _Requires = _Uses<_Alloc>>
        explicit
        priority_queue(const _Alloc& __a)
@@ -592,7 +612,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Alloc, typename _Requires = _Uses<_Alloc>>
        priority_queue(priority_queue&& __q, const _Alloc& __a)
-       : c(std::move(__q.c), __a), comp(std::move(__q.comp)) { }
+       : c(std::move(__q.c), __a), comp(std::move(__q.comp))
+       { __q.c.clear(); }
 #endif
 
       /**
@@ -607,8 +628,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *  the copy according to @a __x.
        *
        *  For more information on function objects, see the
-       *  documentation on @link functors functor base
-       *  classes@endlink.
+       *  documentation on @link functors functor base classes@endlink.
        */
 #if __cplusplus < 201103L
       template<typename _InputIterator>

diff --git a/libstdc++-v3/testsuite/23_containers/priority_queue/118088.cc b/libstdc++-v3/testsuite/23_containers/priority_queue/118088.cc
new file mode 100644 (file)
index 0000000..b59175d
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/priority_queue/118088.cc
@@ -0,0 +1,83 @@
+// { dg-do run { target c++11 } }
+
+#include <queue>
+#include <vector>
+#include <testsuite_hooks.h>
+
+template<typename T, typename Seq>
+bool
+check(std::priority_queue<T, Seq>& p)
+{
+  if (!p.empty())
+    {
+      T prev = p.top();
+      p.pop();
+      while (!p.empty())
+       {
+         if ( prev < p.top() )
+           return false;
+         prev = p.top();
+         p.pop();
+       }
+    }
+  return true;
+}
+
+// A vector-like type that has a non-empty moved-from state.
+struct Vector : std::vector<int>
+{
+  using Base = std::vector<int>;
+
+  using Base::Base;
+
+  Vector(const Vector&) = default;
+  Vector& operator=(const Vector&) = default;
+
+  Vector(Vector&& v) : Base(static_cast<const Base&>(v))
+  {
+    invalidate_heap(v);
+  }
+
+  Vector(Vector&& v, const std::allocator<int>&)
+  : Base(static_cast<const Base&>(v))
+  {
+    invalidate_heap(v);
+  }
+
+  Vector&
+  operator=(Vector&& v)
+  {
+    static_cast<Base&>(*this) = static_cast<const Base&>(v);
+    invalidate_heap(v);
+    return *this;
+  }
+
+  void invalidate_heap(Base& v) { v = {1,2,3}; }
+};
+
+void
+test_moves()
+{
+  std::priority_queue<int, Vector> p;
+  p.push(1);
+  p.push(3);
+  p.push(5);
+  p.push(2);
+  p.push(2);
+  p.push(2);
+  p.push(2);
+  std::priority_queue<int, Vector> p2 = std::move(p);
+  VERIFY( check(p) );
+
+  // Allocator-extended move constructor:
+  std::priority_queue<int, Vector> p3(std::move(p2), std::allocator<int>());
+  VERIFY( check(p2) );
+
+  p2 = std::move(p3);
+  VERIFY( check(p3) );
+}
+
+int main()
+{
+  test_moves();
+}