remove const correctness violations

This is possibly related to a livelock where several threads do const
removal in their respective code paths.

Use the `mutable' specifier for the mutexes and spline's cached data.

Now using the `mutable' specifier, get rid of <optional> in
compat/mutex.

2 files changed, 16 insertions, 20 deletions

diff --git a/compat/copyable-mutex.cpp b/compat/copyable-mutex.cpp
index dde84c83..17b5aa34 100644
--- a/compat/copyable-mutex.cpp
+++ b/compat/copyable-mutex.cpp
@@ -1,18 +1,19 @@
 #include "copyable-mutex.hpp"
+#include <cstdlib>
 
-mutex& mutex::operator=(const mutex& datum)
+mutex& mutex::operator=(const mutex& rhs)
 {
-    inner.emplace(datum->isRecursive() ? QMutex::Recursive : QMutex::NonRecursive);
+    if (rhs->isRecursive() != inner.isRecursive())
+        std::abort();
+
     return *this;
 }
 
-mutex::mutex(const mutex& datum)
+mutex::mutex(const mutex& datum) : mutex{datum.inner.isRecursive() ? Recursive : NonRecursive}
 {
-    *this = datum;
 }
 
-mutex::mutex(mutex::mode m) :
-    inner { std::in_place, static_cast<QMutex::RecursionMode>(int(m)) }
+mutex::mutex(RecursionMode m) : inner{m}
 {
 }
 
@@ -21,13 +22,12 @@ QMutex* mutex::operator&() const
     return *this;
 }
 
-QMutex* mutex::operator->() const
+mutex::operator QMutex*() const
 {
-    return *this;
+    return &inner;
 }
 
-mutex::operator QMutex*() const
+QMutex* mutex::operator->() const
 {
-    return const_cast<QMutex*>(&inner.value());
+    return *this;
 }
-
diff --git a/compat/copyable-mutex.hpp b/compat/copyable-mutex.hpp
index 46c6c88c..37e6802b 100644
--- a/compat/copyable-mutex.hpp
+++ b/compat/copyable-mutex.hpp
@@ -1,25 +1,21 @@
 #pragma once
 
-#include <optional>
-
 #include <QMutex>
 
 #include "export.hpp"
 
 class OTR_COMPAT_EXPORT mutex
 {
-    std::optional<QMutex> inner;
+    mutable QMutex inner;
 
 public:
-    enum mode
-    {
-        recursive = QMutex::Recursive,
-        normal = QMutex::NonRecursive,
-    };
+    using RecursionMode = QMutex::RecursionMode;
+    static constexpr inline RecursionMode Recursive = RecursionMode::Recursive;
+    static constexpr inline RecursionMode NonRecursive = RecursionMode::NonRecursive;
 
     mutex& operator=(const mutex& datum);
     mutex(const mutex& datum);
-    explicit mutex(mode m = normal);
+    explicit mutex(RecursionMode m);
 
     QMutex* operator&() const;
     operator QMutex*() const;