From 1fc7d65aadedb8ec421e788d07e6c00ee023c06b Mon Sep 17 00:00:00 2001
From: Tom <tomut@yahoo.com>
Date: Fri, 8 Jan 2021 12:01:53 -0700
Subject: [PATCH] AK: Add static Singleton::get function to allow destructible
 globals

This enable using global raw pointers rather than Singleton objects,
which solves some problems because global Singleton object could
be deleted when destructors are run.
---
 AK/Singleton.h | 44 +++++++++++++++++++++++++++-----------------
 1 file changed, 27 insertions(+), 17 deletions(-)

diff --git a/AK/Singleton.h b/AK/Singleton.h
index da1305e1c5..615171b855 100644
--- a/AK/Singleton.h
+++ b/AK/Singleton.h
@@ -56,36 +56,46 @@ class Singleton {
 public:
     Singleton() = default;
 
-    T* ptr() const
+    template<bool allow_create = true>
+    static T* get(T*& obj_var)
     {
-        T* obj = AK::atomic_load(&m_obj, AK::memory_order_consume);
+        T* obj = AK::atomic_load(&obj_var, AK::memory_order_acquire);
         if (FlatPtr(obj) <= 0x1) {
             // If this is the first time, see if we get to initialize it
 #ifdef KERNEL
             Kernel::ScopedCritical critical;
 #endif
-            if (obj == nullptr && AK::atomic_compare_exchange_strong(&m_obj, obj, (T*)0x1, AK::memory_order_acq_rel)) {
-                // We're the first one
-                obj = InitFunction();
-                AK::atomic_store(&m_obj, obj, AK::memory_order_release);
-            } else {
-                // Someone else was faster, wait until they're done
-                while (obj == (T*)0x1) {
-#ifdef KERNEL
-                    Kernel::Processor::wait_check();
-#else
-                    // TODO: yield
-#endif
-                    obj = AK::atomic_load(&m_obj, AK::memory_order_consume);
+            if constexpr (allow_create) {
+                if (obj == nullptr && AK::atomic_compare_exchange_strong(&obj_var, obj, (T*)0x1, AK::memory_order_acq_rel)) {
+                    // We're the first one
+                    obj = InitFunction();
+                    AK::atomic_store(&obj_var, obj, AK::memory_order_release);
+                    return obj;
                 }
             }
-            // We should always return an instance
-            ASSERT(obj != nullptr);
+            // Someone else was faster, wait until they're done
+            while (obj == (T*)0x1) {
+#ifdef KERNEL
+                Kernel::Processor::wait_check();
+#else
+                // TODO: yield
+#endif
+                obj = AK::atomic_load(&obj_var, AK::memory_order_acquire);
+            }
+            if constexpr (allow_create) {
+                // We should always return an instance if we allow creating one
+                ASSERT(obj != nullptr);
+            }
             ASSERT(obj != (T*)0x1);
         }
         return obj;
     }
 
+    T* ptr() const
+    {
+        return get(m_obj);
+    }
+
     T* operator->() const
     {
         return ptr();