From c90434962f6a03103a5483808350b63f7d7d6411 Mon Sep 17 00:00:00 2001
From: Wiseguy <68165316+Mr-Wiseguy@users.noreply.github.com>
Date: Sun, 28 Jul 2024 22:00:39 -0400
Subject: [PATCH] Preload executable into memory on Windows to prevent stutters
 (#450)

---
 src/main/main.cpp | 119 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)

diff --git a/src/main/main.cpp b/src/main/main.cpp
index 99d940b..e3dd529 100644
--- a/src/main/main.cpp
+++ b/src/main/main.cpp
@@ -416,8 +416,123 @@ namespace zelda64 {
     }
 }
 
+#ifdef _WIN32
+
+struct PreloadContext {
+    HANDLE handle;
+    HANDLE mapping_handle;
+    SIZE_T size;
+    PVOID view;
+};
+
+bool preload_executable(PreloadContext& context) {
+    wchar_t module_name[MAX_PATH];
+    GetModuleFileNameW(NULL, module_name, MAX_PATH);
+
+    context.handle = CreateFileW(module_name, GENERIC_READ, FILE_SHARE_READ, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
+    if (context.handle == INVALID_HANDLE_VALUE) {
+        fprintf(stderr, "Failed to load executable into memory!");
+        context = {};
+        return false;
+    }
+
+    LARGE_INTEGER module_size;
+    if (!GetFileSizeEx(context.handle, &module_size)) {
+        fprintf(stderr, "Failed to get size of executable!");
+        CloseHandle(context.handle);
+        context = {};
+        return false;
+    }
+
+    context.size = module_size.QuadPart;
+
+    context.mapping_handle = CreateFileMappingW(context.handle, nullptr, PAGE_READONLY, 0, 0, nullptr);
+    if (context.mapping_handle == nullptr) {
+        recompui::message_box("Failed to create file mapping of executable!");
+        CloseHandle(context.handle);
+        context = {};
+        return EXIT_FAILURE;
+    }
+
+    context.view = MapViewOfFile(context.mapping_handle, FILE_MAP_READ, 0, 0, 0);
+    if (context.view == nullptr) {
+        fprintf(stderr, "Failed to map view of of executable!");
+        CloseHandle(context.mapping_handle);
+        CloseHandle(context.handle);
+        context = {};
+        return false;
+    }
+
+    DWORD pid = GetCurrentProcessId();
+    HANDLE process_handle = OpenProcess(PROCESS_SET_QUOTA | PROCESS_QUERY_INFORMATION, FALSE, pid);
+    if (process_handle == nullptr) {
+        fprintf(stderr, "Failed to open own process!");
+        CloseHandle(context.mapping_handle);
+        CloseHandle(context.handle);
+        context = {};
+        return false;
+    }
+
+    SIZE_T minimum_set_size, maximum_set_size;
+    if (!GetProcessWorkingSetSize(process_handle, &minimum_set_size, &maximum_set_size)) {
+        fprintf(stderr, "Failed to get working set size!");
+        CloseHandle(context.mapping_handle);
+        CloseHandle(context.handle);
+        context = {};
+        return false;
+    }
+
+    if (!SetProcessWorkingSetSize(process_handle, minimum_set_size + context.size, maximum_set_size + context.size)) {
+        fprintf(stderr, "Failed to set working set size!");
+        CloseHandle(context.mapping_handle);
+        CloseHandle(context.handle);
+        context = {};
+        return false;
+    }
+
+    if (VirtualLock(context.view, context.size) == 0) {
+        fprintf(stderr, "Failed to lock view of executable! (Error: %08lx)\n", GetLastError());
+        CloseHandle(context.mapping_handle);
+        CloseHandle(context.handle);
+        context = {};
+        return false;
+    }
+    
+    return true;
+}
+
+void release_preload(PreloadContext& context) {
+    VirtualUnlock(context.view, context.size);
+    CloseHandle(context.mapping_handle);
+    CloseHandle(context.handle);
+    context = {};
+}
+
+#else
+
+struct PreloadContext {
+
+};
+
+// TODO implement on other platforms
+bool preload_executable(PreloadContext& context) {
+    return false;
+}
+
+void release_preload(PreloadContext& context) {
+}
+
+#endif
 
 int main(int argc, char** argv) {
+    // Map this executable into memory and lock it, which should keep it in physical memory. This ensures
+    // that there are no stutters from the OS having to load new pages of the executable whenever a new code page is run.
+    PreloadContext preload_context;
+    bool preloaded = preload_executable(preload_context);
+
+    if (!preloaded) {
+        fprintf(stderr, "Failed to preload executable!\n");
+    }
 
 #ifdef _WIN32
     // Set up console output to accept UTF-8 on windows
@@ -518,5 +633,9 @@ int main(int argc, char** argv) {
 
     NFD_Quit();
 
+    if (preloaded) {
+        release_preload(preload_context);
+    }
+
     return EXIT_SUCCESS;
 }