Don't block UI while executing long runnig actions

The previous approach had the problem of losing any action internal
state changes in the created copy.

Revert "Fix temp var values of actions not being accessible"
This reverts commit df42538319.
Revert "Don't block UI while running actions"
This reverts commit a01d26e25d.

lib/utils/sync-helpers.cpp

@@ -66,4 +66,15 @@ void Lockable::WithLock(const std::function<void()> &func)
 	func();
 }
 
+SuspendLock::SuspendLock(Lockable &lockable)
+	: _mtx(static_cast<std::mutex &>(lockable._mtx))
+{
+	_mtx.unlock();
+}
+
+SuspendLock::~SuspendLock()
+{
+	_mtx.lock();
+}
+
 } // namespace advss

lib/utils/sync-helpers.hpp

@@ -51,6 +51,24 @@ public:
 
 private:
 	PerInstanceMutex _mtx;
+
+	friend class SuspendLock;
+};
+
+// RAII guard that temporarily releases a Lockable's per-segment lock.
+// Use this inside PerformAction() / CheckCondition() to unblock the UI
+// during long-running operations while still running on the original segment.
+// The caller MUST be holding the lock (i.e. be inside WithLock) when
+// constructing this object; the lock is re-acquired on destruction.
+class EXPORT SuspendLock {
+public:
+	SuspendLock(Lockable &lockable);
+	~SuspendLock();
+	SuspendLock(const SuspendLock &) = delete;
+	SuspendLock &operator=(const SuspendLock &) = delete;
+
+private:
+	std::mutex &_mtx;
 };
 
 } // namespace advss