Actually remove the Realm from the cache when close() is called

src/impl/apple/cached_realm.cpp

@@ -25,6 +25,7 @@ using namespace realm::_impl;
 
 CachedRealm::CachedRealm(const std::shared_ptr<Realm>& realm, bool cache)
 : m_realm(realm)
+, m_realm_key(realm.get())
 , m_cache(cache)
 {
     struct RefCountedWeakPointer {

src/impl/apple/cached_realm.hpp

@@ -45,14 +45,22 @@ public:
     // Does this CachedRealm store a Realm instance that should be used on the current thread?
     bool is_cached_for_current_thread() const { return m_cache && m_thread_id == std::this_thread::get_id(); }
 
+    // Has the Realm instance been destroyed?
     bool expired() const { return m_realm.expired(); }
 
     // Asyncronously call notify() on the Realm on the appropriate thread
     void notify();
 
+    // Is this a CachedRealm for the given Realm instance?
+    // This should be used rather than lock() to avoid deadlocks when the
+    // reference from lock() is the last remaining one (due to another thread
+    // releasing them at the same time)
+    bool is_for_realm(Realm* realm) const { return realm == m_realm_key; }
+
 private:
     std::weak_ptr<Realm> m_realm;
     std::thread::id m_thread_id = std::this_thread::get_id();
+    void* m_realm_key;
     bool m_cache = false;
 
     CFRunLoopRef m_runloop;

src/impl/realm_coordinator.cpp

@@ -122,16 +122,19 @@ RealmCoordinator::~RealmCoordinator()
     }
 }
 
-void RealmCoordinator::unregister_realm(Realm*)
+void RealmCoordinator::unregister_realm(Realm* realm)
 {
     std::lock_guard<std::mutex> lock(m_realm_mutex);
     for (size_t i = 0; i < m_cached_realms.size(); ++i) {
-        if (m_cached_realms[i].expired()) {
-            if (i + 1 < m_cached_realms.size()) {
-                m_cached_realms[i] = std::move(m_cached_realms.back());
-            }
-            m_cached_realms.pop_back();
+        auto& cached_realm = m_cached_realms[i];
+        if (!cached_realm.expired() && !cached_realm.is_for_realm(realm)) {
+            continue;
         }
+
+        if (i + 1 < m_cached_realms.size()) {
+            cached_realm = std::move(m_cached_realms.back());
+        }
+        m_cached_realms.pop_back();
     }
 }