Spinlock+LockedValue: Add try_lock() methods

For when you want to lock a resource if possible but not get blocked if it is locked by another thread.

kernel/src/memory/KernelVM.cpp

@@ -21,8 +21,6 @@ namespace KernelVM
 {
     void init()
     {
-        g_kernelvm_bitmap.init();
-
         auto kernelvm_bitmap = g_kernelvm_bitmap.lock();
         kernelvm_bitmap->initialize(bitmap_memory, sizeof(bitmap_memory));
         kernelvm_bitmap->clear(false);

kernel/src/memory/MemoryManager.cpp

@@ -53,8 +53,6 @@ namespace MemoryManager
         MemoryMapIterator iter;
         MemoryMapEntry entry;
 
-        g_frame_bitmap.init();
-
         const auto largest_free_entry = iter.largest_free();
 
         expect(largest_free_entry.is_free(), "We were given a largest free memory region that isn't even free!");

kernel/src/thread/Spinlock.cpp

@@ -4,18 +4,24 @@
 
 void Spinlock::lock()
 {
-    int expected = -1;
+    int expected = 0;
-    while (!m_lock.compare_exchange_strong(expected, 0))
+    while (!m_lock.compare_exchange_strong(expected, 1))
     {
-        expected = -1;
+        expected = 0;
         CPU::pause();
     }
 }
 
-void Spinlock::unlock()
+bool Spinlock::try_lock()
 {
     int expected = 0;
-    if (!m_lock.compare_exchange_strong(expected, -1))
+    return m_lock.compare_exchange_strong(expected, 1);
+}
+
+void Spinlock::unlock()
+{
+    int expected = 1;
+    if (!m_lock.compare_exchange_strong(expected, 0))
     {
         kwarnln("Spinlock::unlock() called on an unlocked lock with value %d", expected);
     }

kernel/src/thread/Spinlock.h

@@ -1,5 +1,6 @@
 #pragma once
 #include <luna/Atomic.h>
+#include <luna/Option.h>
 
 class Spinlock
 {
@@ -7,37 +8,41 @@ class Spinlock
     void lock();
     void unlock();
 
+    bool try_lock();
+
     bool is_locked() const
     {
-        return m_lock.load() != -1;
+        return m_lock.load() != 0;
-    }
-
-    // Call this before use if the Spinlock is a global variable.
-    void init()
-    {
-        m_lock = -1;
     }
 
   private:
-    Atomic<int> m_lock{-1};
+    Atomic<int> m_lock{0};
 };
 
 template <typename T> class LockedValue
 {
     struct LockedValueGuard
     {
-        LockedValueGuard(LockedValue& value_ref) : m_value_ref(value_ref)
+        LockedValueGuard(LockedValue& value_ref) : m_value_ref(&value_ref)
         {
         }
 
+        LockedValueGuard(const LockedValueGuard& other) = delete;
+        LockedValueGuard(LockedValueGuard&& other)
+        {
+            m_value_ref = other.m_value_ref;
+            other.m_value_ref = nullptr;
+        }
+
         ~LockedValueGuard()
         {
-            m_value_ref.m_lock.unlock();
+            if (m_value_ref) m_value_ref->m_lock.unlock();
         }
 
         T& ref()
         {
-            return m_value_ref.m_value;
+            expect(m_value_ref, "LockedValueGuard::ref() called on a moved LockedValueGuard");
+            return m_value_ref->m_value;
         }
 
         void set(const T& other)
@@ -56,7 +61,7 @@ template <typename T> class LockedValue
         }
 
       private:
-        LockedValue& m_value_ref;
+        LockedValue* m_value_ref;
     };
 
   public:
@@ -68,18 +73,18 @@ template <typename T> class LockedValue
     {
     }
 
-    // Call this before use if the LockedValue is a global variable.
-    void init()
-    {
-        m_lock.init();
-    }
-
     LockedValueGuard lock()
     {
         m_lock.lock();
         return {*this};
     }
 
+    Option<LockedValueGuard> try_lock()
+    {
+        if (m_lock.try_lock()) { return {*this}; }
+        return {};
+    }
+
   private:
     T m_value;
     Spinlock m_lock;