From c147cb2a949d2a5c75804613c45e46c1a2ec8ab1 Mon Sep 17 00:00:00 2001
From: Steven Le Rouzic <steven.lerouzic@gmail.com>
Date: Sat, 20 Apr 2024 01:22:04 +0200
Subject: Temporary allocator

---
 deimos/core/temp_allocator.cpp | 109 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 deimos/core/temp_allocator.cpp

(limited to 'deimos/core/temp_allocator.cpp')

diff --git a/deimos/core/temp_allocator.cpp b/deimos/core/temp_allocator.cpp
new file mode 100644
index 0000000..2f07bcc
--- /dev/null
+++ b/deimos/core/temp_allocator.cpp
@@ -0,0 +1,109 @@
+#include "deimos/core/temp_allocator.h"
+
+#include "deimos/core/api_registry.h"
+#include "deimos/core/allocator.h"
+#include "deimos/core/os.h"
+
+static deimos::OsApi* os_api;
+
+namespace deimos
+{
+
+class TempAllocatorImpl : public ITempAllocator
+{
+    static constexpr int64_t kDefaultAlign    = 8;
+    static constexpr int64_t kPageSize        = 1 * Megabytes;
+    static constexpr int64_t kReserveSize     = 256 * Megabytes;
+    
+    gsl::owner<void*> m_base{};
+    void*             m_commit_end{};
+    void*             m_reserve_end{};
+
+    // @Todo Last allocation optimization
+    void*             m_current{};
+    
+public:
+    gsl::owner<void*> Reallocate(TempAllocatorTag tag,
+        gsl::owner<void*> old_ptr, int64_t old_size, int64_t new_size) override
+    {
+        void* tag_ptr = std::bit_cast<void*>(tag.tag);
+        Expects(tag_ptr >= m_base && tag_ptr <= m_commit_end && tag_ptr <= m_current);
+        
+        if (new_size <= old_size) { return (new_size == 0) ? nullptr : old_ptr; }
+
+        void* new_current = OffsetBytes(m_current, AlignUp(new_size, kDefaultAlign));
+        if (new_current > m_reserve_end)
+        {
+            deimos_Panic("Ran out of temporary memory");
+            return nullptr;
+        }
+
+        if (new_current > m_commit_end)
+        {
+            const int64_t new_commit_size = AlignUp(
+                (uint64_t)(std::bit_cast<uintptr_t>(new_current) - std::bit_cast<uintptr_t>(m_base)), // NOLINT
+                kPageSize);
+            os_api->virtual_memory->Commit(m_base, new_commit_size);
+            m_commit_end = OffsetBytes(m_base, new_commit_size);
+            Ensures(m_commit_end <= m_reserve_end);
+        }
+
+        if (old_ptr != nullptr)
+        {
+            MemoryCopy(m_current, old_ptr, old_size);
+        }
+        
+        return std::exchange(m_current, new_current);
+    }
+    
+    TempAllocator Acquire()
+    {
+        if (m_base == nullptr)
+        {
+            m_base        = os_api->virtual_memory->Reserve(kReserveSize);
+            m_current     = m_base;
+            m_commit_end  = m_base;
+            m_reserve_end = OffsetBytes(m_base, kReserveSize);
+        }
+        
+        return TempAllocator(this, {std::bit_cast<uintptr_t>(m_current)});
+    }
+    
+    void Release(TempAllocatorTag tag) override
+    {
+        void* rewind_base = std::bit_cast<void*>(tag.tag);
+        Expects(rewind_base >= m_base && rewind_base <= m_commit_end);
+        
+        if (rewind_base < m_current)
+        {
+            m_current = rewind_base;
+        }
+        else
+        {
+            deimos_Panic("Invalid temporary allocator rewind");
+        }
+    }
+};
+
+static thread_local TempAllocatorImpl g_impl;
+
+class TempAllocatorApiImpl : public TempAllocatorApi
+{
+public:
+    TempAllocator Acquire() override
+    {
+        return g_impl.Acquire();
+    }
+};
+
+void RegisterTempAllocatorApi(ApiRegistry* api_registry)
+{
+    os_api = api_registry->Get<OsApi>();
+    
+    auto* allocator = api_registry->Get<AllocatorApi>()->system;
+    gsl::owner<TempAllocatorApi*> temp_allocator_api = allocator->New<TempAllocatorApiImpl>();
+    api_registry->Set(temp_allocator_api);
+}
+
+} // namespace deimos
+
-- 
cgit