global: implemented rudimentary memory manager to use available system memory

without forcing the OS to page swap

app/render/CMakeLists.txt

@@ -26,6 +26,8 @@ set(OLIVE_SOURCES
   render/colorprocessor.cpp
   render/diskmanager.h
   render/diskmanager.cpp
+  render/memorymanager.h
+  render/memorymanager.cpp
   render/pixelformat.h
   render/pixelformat.cpp
   render/pixelservice.h

app/render/memorymanager.cpp

@@ -0,0 +1,58 @@
+#include "memorymanager.h"
+
+#include <QDebug>
+
+#ifdef Q_OS_WINDOWS
+#include <windows.h>
+#endif
+
+MemoryManager* MemoryManager::instance_ = nullptr;
+
+const uint64_t MemoryManager::minimum_available_memory_ = 2147483648;
+
+MemoryManager::MemoryManager(QObject* parent) :
+  QObject(parent)
+{
+}
+
+void MemoryManager::CreateInstance()
+{
+  instance_ = new MemoryManager();
+}
+
+MemoryManager *MemoryManager::instance()
+{
+  return instance_;
+}
+
+void MemoryManager::DestroyInstance()
+{
+  delete instance_;
+  instance_ = nullptr;
+}
+
+bool MemoryManager::ShouldFreeMemory()
+{
+  return (GetAvailableMemory() < minimum_available_memory_);
+}
+
+void MemoryManager::ConsumedMemory()
+{
+  if (ShouldFreeMemory()) {
+    emit FreeMemory();
+  }
+}
+
+uint64_t MemoryManager::GetAvailableMemory()
+{
+#ifdef Q_OS_WINDOWS
+  MEMORYSTATUSEX status;
+  status.dwLength = sizeof(status);
+  GlobalMemoryStatusEx(&status);
+  return status.ullAvailPhys;
+#else
+  long pages = sysconf(_SC_PHYS_PAGES);
+  long page_size = sysconf(_SC_PAGE_SIZE);
+  return pages * page_size;
+#endif
+}

app/render/memorymanager.h

@@ -0,0 +1,33 @@
+#ifndef MEMORYMANAGER_H
+#define MEMORYMANAGER_H
+
+#include <QObject>
+
+class MemoryManager : public QObject
+{
+  Q_OBJECT
+public:
+  MemoryManager(QObject* parent = nullptr);
+
+  static void CreateInstance();
+  static MemoryManager* instance();
+  static void DestroyInstance();
+
+  static bool ShouldFreeMemory();
+
+public slots:
+  void ConsumedMemory();
+
+signals:
+  void FreeMemory();
+
+private:
+  static uint64_t GetAvailableMemory();
+
+  static MemoryManager* instance_;
+
+  static const uint64_t minimum_available_memory_;
+
+};
+
+#endif // MEMORYMANAGER_H