Implement RomFS cache and async reads. (#7089)

* Implement RomFS cache and async reads.

* Suggestions and fix compilation.

* Apply suggestions

src/common/CMakeLists.txt

@@ -124,6 +124,7 @@ add_library(citra_common STATIC
     serialization/boost_flat_set.h
     serialization/boost_small_vector.hpp
     serialization/boost_vector.hpp
+    static_lru_cache.h
     string_literal.h
     string_util.cpp
     string_util.h

src/common/file_util.cpp

@@ -1155,6 +1155,43 @@ std::size_t IOFile::ReadImpl(void* data, std::size_t length, std::size_t data_si
     return std::fread(data, data_size, length, m_file);
 }
 
+#ifdef _WIN32
+static std::size_t pread(int fd, void* buf, size_t count, uint64_t offset) {
+    long unsigned int read_bytes = 0;
+    OVERLAPPED overlapped = {0};
+    HANDLE file = reinterpret_cast<HANDLE>(_get_osfhandle(fd));
+
+    overlapped.OffsetHigh = static_cast<uint32_t>(offset >> 32);
+    overlapped.Offset = static_cast<uint32_t>(offset & 0xFFFF'FFFFLL);
+    SetLastError(0);
+    bool ret = ReadFile(file, buf, static_cast<uint32_t>(count), &read_bytes, &overlapped);
+
+    if (!ret && GetLastError() != ERROR_HANDLE_EOF) {
+        errno = GetLastError();
+        return std::numeric_limits<std::size_t>::max();
+    }
+    return read_bytes;
+}
+#else
+#define pread ::pread
+#endif
+
+std::size_t IOFile::ReadAtImpl(void* data, std::size_t length, std::size_t data_size,
+                               std::size_t offset) {
+    if (!IsOpen()) {
+        m_good = false;
+        return std::numeric_limits<std::size_t>::max();
+    }
+
+    if (length == 0) {
+        return 0;
+    }
+
+    DEBUG_ASSERT(data != nullptr);
+
+    return pread(fileno(m_file), data, data_size * length, offset);
+}
+
 std::size_t IOFile::WriteImpl(const void* data, std::size_t length, std::size_t data_size) {
     if (!IsOpen()) {
         m_good = false;

src/common/file_util.h

@@ -294,6 +294,18 @@ public:
         return items_read;
     }
 
+    template <typename T>
+    std::size_t ReadAtArray(T* data, std::size_t length, std::size_t offset) {
+        static_assert(std::is_trivially_copyable_v<T>,
+                      "Given array does not consist of trivially copyable objects");
+
+        std::size_t items_read = ReadAtImpl(data, length, sizeof(T), offset);
+        if (items_read != length)
+            m_good = false;
+
+        return items_read;
+    }
+
     template <typename T>
     std::size_t WriteArray(const T* data, std::size_t length) {
         static_assert(std::is_trivially_copyable_v<T>,
@@ -312,6 +324,12 @@ public:
         return ReadArray(reinterpret_cast<char*>(data), length);
     }
 
+    template <typename T>
+    std::size_t ReadAtBytes(T* data, std::size_t length, std::size_t offset) {
+        static_assert(std::is_trivially_copyable_v<T>, "T must be trivially copyable");
+        return ReadAtArray(reinterpret_cast<char*>(data), length, offset);
+    }
+
     template <typename T>
     std::size_t WriteBytes(const T* data, std::size_t length) {
         static_assert(std::is_trivially_copyable_v<T>, "T must be trivially copyable");
@@ -363,6 +381,8 @@ public:
 
 private:
     std::size_t ReadImpl(void* data, std::size_t length, std::size_t data_size);
+    std::size_t ReadAtImpl(void* data, std::size_t length, std::size_t data_size,
+                           std::size_t offset);
     std::size_t WriteImpl(const void* data, std::size_t length, std::size_t data_size);
 
     bool Open();

src/common/static_lru_cache.h

@@ -0,0 +1,113 @@
+// Modified version of: https://www.boost.org/doc/libs/1_79_0/boost/compute/detail/lru_cache.hpp
+// Most important change is the use of an array instead of a map, so that elements are
+// statically allocated. The insert and get methods have been merged into the request method.
+// Original license:
+//
+//---------------------------------------------------------------------------//
+// Copyright (c) 2013 Kyle Lutz <kyle.r.lutz@gmail.com>
+//
+// Distributed under the Boost Software License, Version 1.0
+// See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt
+//
+// See http://boostorg.github.com/compute for more information.
+//---------------------------------------------------------------------------//
+#pragma once
+
+#include <array>
+#include <list>
+#include <tuple>
+#include <utility>
+
+namespace Common {
+
+// a cache which evicts the least recently used item when it is full
+// the cache elements are statically allocated.
+template <class Key, class Value, size_t Size>
+class StaticLRUCache {
+public:
+    using key_type = Key;
+    using value_type = Value;
+    using list_type = std::list<std::pair<Key, size_t>>;
+    using array_type = std::array<Value, Size>;
+
+    StaticLRUCache() = default;
+
+    ~StaticLRUCache() = default;
+
+    size_t size() const {
+        return m_list.size();
+    }
+
+    constexpr size_t capacity() const {
+        return m_array.size();
+    }
+
+    bool empty() const {
+        return m_list.empty();
+    }
+
+    bool contains(const key_type& key) const {
+        return find(key) != m_list.end();
+    }
+
+    // Requests an element from the cache. If it is not found,
+    // the element is inserted using its key.
+    // Returns whether the element was present in the cache
+    // and a reference to the element itself.
+    std::pair<bool, value_type&> request(const key_type& key) {
+        // lookup value in the cache
+        auto i = find(key);
+        if (i == m_list.cend()) {
+            size_t next_index = size();
+            // insert item into the cache, but first check if it is full
+            if (next_index >= capacity()) {
+                // cache is full, evict the least recently used item
+                next_index = evict();
+            }
+
+            // insert the new item
+            m_list.push_front(std::make_pair(key, next_index));
+            return std::pair<bool, value_type&>(false, m_array[next_index]);
+        }
+        // return the value, but first update its place in the most
+        // recently used list
+        if (i != m_list.cbegin()) {
+            // move item to the front of the most recently used list
+            auto backup = *i;
+            m_list.erase(i);
+            m_list.push_front(backup);
+
+            // return the value
+            return std::pair<bool, value_type&>(true, m_array[backup.second]);
+        } else {
+            // the item is already at the front of the most recently
+            // used list so just return it
+            return std::pair<bool, value_type&>(true, m_array[i->second]);
+        }
+    }
+
+    void clear() {
+        m_list.clear();
+    }
+
+private:
+    typename list_type::const_iterator find(const key_type& key) const {
+        return std::find_if(m_list.cbegin(), m_list.cend(),
+                            [&key](const auto& el) { return el.first == key; });
+    }
+
+    size_t evict() {
+        // evict item from the end of most recently used list
+        typename list_type::iterator i = --m_list.end();
+        size_t evicted_index = i->second;
+        m_list.erase(i);
+        return evicted_index;
+    }
+
+private:
+    array_type m_array;
+    list_type m_list;
+};
+
+} // namespace Common