ListenerList: Optimise empty listener list

modules/juce_core/containers/juce_ListenerList.h

@@ -111,6 +111,8 @@ class ListenerList
  */
  void add (ListenerClass* listenerToAdd)
  {
+ initialiseIfNeeded();
+
  if (listenerToAdd != nullptr)
  listeners->addIfNotAlreadyThere (listenerToAdd);
  else
@@ -127,6 +129,9 @@ class ListenerList
  {
  jassert (listenerToRemove != nullptr); // Listeners can't be null pointers!
 
+ if (! initialised())
+ return;
+
  const ScopedLockType lock (listeners->getLock());
 
  if (const auto index = listeners->removeFirstMatchingValue (listenerToRemove); index >= 0)
@@ -154,10 +159,10 @@ class ListenerList
  }
 
  /** Returns the number of registered listeners. */
- int size() const noexcept { return listeners->size(); }
+ int size() const noexcept { return ! initialised() ? 0 : listeners->size(); }
 
  /** Returns true if no listeners are registered, false otherwise. */
- bool isEmpty() const noexcept { return listeners->isEmpty(); }
+ bool isEmpty() const noexcept { return ! initialised() || listeners->isEmpty(); }
 
  /** Clears the list.
 
@@ -166,7 +171,8 @@ class ListenerList
  */
  void clear()
  {
- const ScopedLockType lock (listeners->getLock());
+ if (! initialised())
+ return;
 
  listeners->clear();
 
@@ -175,7 +181,11 @@ class ListenerList
  }
 
  /** Returns true if the specified listener has been added to the list. */
- bool contains (ListenerClass* listener) const noexcept { return listeners->contains (listener); }
+ bool contains (ListenerClass* listener) const noexcept
+ {
+ return initialised()
+ && listeners->contains (listener);
+ }
 
  /** Returns the raw array of listeners.
 
@@ -186,7 +196,11 @@ class ListenerList
 
  @see add, remove, clear, contains
  */
- const ArrayType& getListeners() const noexcept { return *listeners; }
+ const ArrayType& getListeners() const noexcept
+ {
+ const_cast<ListenerList*> (this)->initialiseIfNeeded();
+ return *listeners;
+ }
 
  //==============================================================================
  /** Calls an invokable object for each listener in the list. */
@@ -234,6 +248,9 @@ class ListenerList
  const BailOutCheckerType& bailOutChecker,
  Callback&& callback)
  {
+ if (! initialised())
+ return;
+
  const auto localListeners = listeners;
  const ScopedLockType lock { localListeners->getLock() };
 
@@ -339,7 +356,7 @@ class ListenerList
 
  //==============================================================================
  using SharedListeners = std::shared_ptr<ArrayType>;
- const SharedListeners listeners = std::make_shared<ArrayType>();
+ SharedListeners listeners;
 
  struct Iterator
  {
@@ -349,7 +366,37 @@ class ListenerList
 
  using SafeIterators = std::vector<Iterator*>;
  using SharedIterators = std::shared_ptr<SafeIterators>;
- const SharedIterators iterators = std::make_shared<SafeIterators>();
+ SharedIterators iterators;
+
+ enum class State
+ {
+ uninitialised,
+ initialising,
+ initialised
+ };
+
+ std::atomic<State> state { State::uninitialised };
+
+ inline bool initialised() const noexcept { return state == State::initialised; }
+
+ inline void initialiseIfNeeded() noexcept
+ {
+ if (initialised())
+ return;
+
+ auto expected = State::uninitialised;
+
+ if (state.compare_exchange_strong (expected, State::initialising))
+ {
+ listeners = std::make_shared<ArrayType>();
+ iterators = std::make_shared<SafeIterators>();
+ state = State::initialised;
+ return;
+ }
+
+ while (! initialised())
+ std::this_thread::yield();
+ }
 
  //==============================================================================
  JUCE_DECLARE_NON_COPYABLE (ListenerList)