fix for Latch race (#617)

Because the counter is decreased in `CountDown()` and subsequently checked against zero to determine if the completion event should be set:

`Latch::Wait` checks the counter against zero on entry and would exit early, before waiting on the completion event. This could then lead to the `Latch` instance being torn down before the `CountDown()` does a `Set()` which could then lead to unexpected and unwanted things happening.

1 files changed, 11 insertions, 21 deletions

diff --git a/src/zencore/include/zencore/thread.h b/src/zencore/include/zencore/thread.h
index 11ef01a35..9fe6dfb9b 100644
--- a/src/zencore/include/zencore/thread.h
+++ b/src/zencore/include/zencore/thread.h
@@ -103,16 +103,12 @@ public:
 	ZENCORE_API Event();
 	ZENCORE_API ~Event();
 
-	Event(Event&& Rhs) noexcept : m_EventHandle(Rhs.m_EventHandle) { Rhs.m_EventHandle = nullptr; }
+	Event(Event&& Rhs) noexcept : m_EventHandle(Rhs.m_EventHandle.load()) { Rhs.m_EventHandle = nullptr; }
 
 	Event(const Event& Rhs) = delete;
 	Event& operator=(const Event& Rhs) = delete;
 
-	inline Event& operator=(Event&& Rhs) noexcept
-	{
-		std::swap(m_EventHandle, Rhs.m_EventHandle);
-		return *this;
-	}
+	Event& operator=(Event&& Rhs) = delete;
 
 	ZENCORE_API void Set();
 	ZENCORE_API void Reset();
@@ -126,7 +122,7 @@ public:
 protected:
 	explicit Event(void* EventHandle) : m_EventHandle(EventHandle) {}
 
-	void* m_EventHandle = nullptr;
+	std::atomic<void*> m_EventHandle{nullptr};
 };
 
 /** Basic abstraction of an IPC mechanism (aka 'binary semaphore')
@@ -141,16 +137,18 @@ public:
 	ZENCORE_API std::error_code Set();
 	ZENCORE_API bool			Wait(int TimeoutMs = -1);
 
-	NamedEvent(NamedEvent&& Rhs) noexcept : m_EventHandle(Rhs.m_EventHandle) { Rhs.m_EventHandle = nullptr; }
+	NamedEvent(NamedEvent&& Rhs) noexcept : m_EventHandle(Rhs.m_EventHandle.load()) { Rhs.m_EventHandle = nullptr; }
 
-	inline NamedEvent& operator=(NamedEvent&& Rhs) noexcept
+	NamedEvent& operator=(NamedEvent&& Rhs)
 	{
-		std::swap(m_EventHandle, Rhs.m_EventHandle);
+		Close();
+		m_EventHandle	  = Rhs.m_EventHandle.load();
+		Rhs.m_EventHandle = nullptr;
 		return *this;
-	}
+	};
 
 protected:
-	void* m_EventHandle = nullptr;
+	std::atomic<void*> m_EventHandle{nullptr};
 
 private:
 	NamedEvent(const NamedEvent& Rhs) = delete;
@@ -201,15 +199,7 @@ public:
 		ZEN_ASSERT(Old > 0);
 	}
 
-	bool Wait(int TimeoutMs = -1)
-	{
-		std::ptrdiff_t Old = Counter.load();
-		if (Old == 0)
-		{
-			return true;
-		}
-		return Complete.Wait(TimeoutMs);
-	}
+	bool Wait(int TimeoutMs = -1) { return Complete.Wait(TimeoutMs); }
 
 private:
 	std::atomic_ptrdiff_t Counter;