[debug] Add "Iterating" helper to avoid calling erase() when iterating a obs::fast_list

Author: dacap

obs/fast_list.h

@@ -9,6 +9,7 @@
 #pragma once
 
 #include <algorithm>
+#include <cassert>
 #include <functional>
 #include <vector>
 
@@ -17,6 +18,9 @@ namespace obs {
 template<typename T>
 class fast_list {
   std::vector<T*> m_list;
+#ifndef NDEBUG
+  int m_iterating = 0;
+#endif
 
 public:
   using iterator = typename std::vector<T*>::iterator;
@@ -33,10 +37,21 @@ class fast_list {
   }
 
   void erase(T* value) {
+    assert(m_iterating == 0);
     auto it = std::find(m_list.begin(), m_list.end(), value);
     if (it != m_list.end())
       m_list.erase(it);
   }
+
+#ifndef NDEBUG
+  void set_iterating(const bool state) {
+    if (state)
+      ++m_iterating;
+    else
+      --m_iterating;
+  }
+#endif
+
 };
 
 } // namespace obs

obs/lists.h

@@ -21,6 +21,19 @@ namespace obs {
   using default_list = safe_list<T>;
 #endif
 
+#ifdef _DEBUG
+template<typename List>
+struct Iterating {
+  List& m_list;
+  Iterating(List& list) : m_list(list) {
+    m_list.set_iterating(true);
+  }
+  ~Iterating() {
+    m_list.set_iterating(false);
+  }
+};
+#endif
+
 } // namespace obs
 
 #endif

obs/observers.h

@@ -32,6 +32,9 @@ class observers {
 
   template<typename ...Args>
   void notify_observers(void (observer_type::*method)(Args...), Args ...args) {
+#ifdef _DEBUG
+    Iterating<list_type> flag(m_observers);
+#endif
     for (auto observer : m_observers) {
       if (observer)
         (observer->*method)(std::forward<Args>(args)...);

obs/safe_list.h

@@ -359,6 +359,13 @@ class safe_list {
       delete_nodes(false);
   }
 
+#ifndef NDEBUG
+  void set_iterating(const bool) {
+    // No need to set a flag here for debugging purposes as we support
+    // calling erase() member function when we're iterating the items.
+  }
+#endif
+
 private:
   // Deletes nodes from the list. If "all" is true, deletes all nodes,
   // if it's false, it deletes only nodes with value == nullptr, which

obs/signal.h

@@ -70,6 +70,9 @@ class signal<R(Args...), List> : public signal_base {
   template<typename U = R, typename...Args2>
   typename std::enable_if<std::is_void<U>::value, void>::type
   operator()(Args2&&...args) {
+#ifdef _DEBUG
+    Iterating<slot_list> flag(m_slots);
+#endif
     for (auto slot : m_slots)
       if (slot)
         (*slot)(std::forward<Args2>(args)...);
@@ -78,6 +81,9 @@ class signal<R(Args...), List> : public signal_base {
   template<typename U = R, typename...Args2>
   typename std::enable_if<!std::is_void<U>::value, U>::type
   operator()(Args2&&...args) {
+#ifdef _DEBUG
+    Iterating<slot_list> flag(m_slots);
+#endif
     U result = {};
     for (auto slot : m_slots)
       if (slot)