event/Loop: add flag "dead"

src/event/Loop.cxx

@@ -25,7 +25,9 @@
 #include "util/ScopeExit.hxx"
 
 EventLoop::EventLoop(ThreadId _thread)
-	:SocketMonitor(*this), quit(false), thread(_thread)
+	:SocketMonitor(*this),
+	 quit(false), dead(false),
+	 thread(_thread)
 {
 	SocketMonitor::Open(SocketDescriptor(wake_fd.Get()));
 }
@@ -142,10 +144,14 @@ EventLoop::Run() noexcept
 
 	assert(IsInside());
 	assert(!quit);
+	assert(!dead);
 	assert(busy);
 
 	SocketMonitor::Schedule(SocketMonitor::READ);
-	AtScopeExit(this) { SocketMonitor::Cancel(); };
+	AtScopeExit(this) {
+		dead = true;
+		SocketMonitor::Cancel();
+	};
 
 	do {
 		now = std::chrono::steady_clock::now();
@@ -210,6 +216,7 @@ EventLoop::Run() noexcept
 	} while (!quit);
 
 #ifndef NDEBUG
+	assert(!dead);
 	assert(busy);
 	assert(thread.IsInside());
 #endif

src/event/Loop.hxx

@@ -88,6 +88,11 @@ class EventLoop final : SocketMonitor
 
 	std::atomic_bool quit;
 
+	/**
+	 * If this is true, then Run() has returned.
+	 */
+	std::atomic_bool dead;
+
 	/**
 	 * True when the object has been modified and another check is
 	 * necessary before going to sleep via PollGroup::ReadEvents().
@@ -199,6 +204,10 @@ private:
 	bool OnSocketReady(unsigned flags) noexcept override;
 
 public:
+	gcc_pure
+	bool IsDead() const noexcept {
+		return dead;
+	}
 
 	/**
 	 * Are we currently running inside this EventLoop's thread?