options/tie: fix deadlocks

1 files changed, 19 insertions, 3 deletions

diff --git a/options/value.hpp b/options/value.hpp
index 10903b19..849611d3 100644
--- a/options/value.hpp
+++ b/options/value.hpp
@@ -39,7 +39,9 @@ template<typename t>
 class value final : public value_
 {
     static_assert(std::is_same_v<t, remove_cvref_t<t>>);
+    mutable QMutex mtx;
     const t def;
+    mutable t cached_value = def;
     using traits = detail::value_traits<t>;
 
     never_inline
@@ -95,10 +97,24 @@ public:
     never_inline
     void notify() const override
     {
-        if (!is_null())
-        {
+        if (is_null())
+            return;
+
+        auto x = get();
+
+        bool b = progn(
+            QMutexLocker l(&mtx);
+            if (!traits::is_equal(x, cached_value))
+            {
+                cached_value = x;
+                return true;
+            }
+            return false;
+        );
+
+        if (b) {
             maybe_trace(true);
-            emit valueChanged(traits::storage_from_value(get()));
+            emit valueChanged(traits::storage_from_value(x));
             maybe_trace(false);
         }
     }