options: don't notify on idempotent values

3 files changed, 24 insertions, 9 deletions

diff --git a/options/base-value.cpp b/options/base-value.cpp
index c7691a8f..9ccbbdf8 100644
--- a/options/base-value.cpp
+++ b/options/base-value.cpp
@@ -26,9 +26,8 @@ value_::~value_()
     b->on_value_destructed(this);
 }
 
-void value_::maybe_trace(bool x) const
+void value_::maybe_trace(const char* str) const
 {
     if (TRACE_NOTIFY)
-        qDebug().noquote() << "notify" << (x ? '+' : '-')
-                           << QThread::currentThreadId() << b->name() << self_name;
+        qDebug().noquote() << str << QThread::currentThreadId() << b->name() << self_name;
 }
diff --git a/options/base-value.hpp b/options/base-value.hpp
index 9b2ebe53..6365f82a 100644
--- a/options/base-value.hpp
+++ b/options/base-value.hpp
@@ -67,7 +67,7 @@ protected:
     virtual void store_variant(QVariant&&) noexcept = 0;
     virtual void store_variant(const QVariant&) noexcept = 0;
 
-    void maybe_trace(bool x) const;
+    void maybe_trace(const char* str) const;
 
     template<typename t>
     void store_(const t& datum)
diff --git a/options/value.hpp b/options/value.hpp
index 10903b19..85b76cb6 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;
     using traits = detail::value_traits<t>;
 
     never_inline
@@ -95,11 +97,25 @@ public:
     never_inline
     void notify() const override
     {
-        if (!is_null())
+        if (is_null())
+            return;
+
+        auto x = get();
         {
-            maybe_trace(true);
-            emit valueChanged(traits::storage_from_value(get()));
-            maybe_trace(false);
+            QMutexLocker l(&mtx);
+            if (traits::is_equal(x, cached_value))
+            {
+                //maybe_trace("notify ~");
+                return;
+            }
+            else
+            {
+                cached_value = x;
+                l.unlock();
+                maybe_trace("notify +");
+                emit valueChanged(traits::storage_from_value(x));
+                maybe_trace("notify -");
+            }
         }
     }
 
@@ -131,7 +147,7 @@ public:
     static constexpr Qt::ConnectionType DIRECT_CONNTYPE = Qt::DirectConnection;
     static constexpr Qt::ConnectionType SAFE_CONNTYPE = Qt::QueuedConnection;
 
-    value(bundle b, const QString& name, t def) noexcept : value_(b, name), def(std::move(def))
+    value(bundle b, const QString& name, t def) noexcept : value_(b, name), def(std::move(def)), cached_value{get()}
     {
     }