//// Dis VM// File: fd_manager.cpp// Author: arr// #include <array>#include <mutex>#include <unordered_map>#include <exceptions.h>#include <vm_memory.h>#include "sys_utils.h" using namespace disvm::runtime; namespace{    using fd_map_t = std::unordered_map<word_t, vm_alloc_t *>;     auto std_fd = std::array<vm_alloc_t * , 3>    {        nullptr, // stdin        nullptr, // stdout        nullptr, // stderr    };     auto next_fd = word_t{ 0 };     std::mutex fd_map_lock;    auto fd_map = fd_map_t{};} word_t disvm::runtime::sys::create_fd_record(vm_alloc_t * fd_alloc){    assert(fd_alloc != nullptr);     {        std::lock_guard<std::mutex> lock{ fd_map_lock };         auto new_fd = next_fd;        next_fd++;        if (new_fd < static_cast<word_t>(std_fd.size()))        {            std_fd[new_fd] = fd_alloc;        }        else        {            assert(fd_map.cend() == fd_map.find(new_fd));            fd_map[new_fd] = fd_alloc;        }         return new_fd;    }} vm_alloc_t * disvm::runtime::sys::fetch_fd_record(word_t fd){    assert(fd != sys::vm_invalid_fd && "Invalid FD value");     if (0 <= fd && fd < static_cast<word_t>(std_fd.size()))        return std_fd[fd];     {        std::lock_guard<std::mutex> lock{ fd_map_lock };        auto iter = fd_map.find(fd);        if (iter == fd_map.cend())            throw vm_user_exception{ "Unknown file descriptor" };         return iter->second;    }} void disvm::runtime::sys::drop_fd_record(word_t fd){    assert(fd != sys::vm_invalid_fd && "Invalid FD value");    assert(fd >= static_cast<word_t>(std_fd.size()) && "Request to drop std file?");     {        std::lock_guard<std::mutex> lock{ fd_map_lock };        auto iter = fd_map.find(fd);        if (iter != fd_map.cend())            fd_map.erase(iter);    }}