Rewrite the template into a somewhat modern C++

LICENSE

@@ -2,6 +2,7 @@ MIT License
 
 Copyright (c) 2022 Joel Matejka
 Copyright (c) 2023 Jiri Vlasak
+Copyright (c) 2023 Matej Kafka
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

meson.build

 project('esw04-epoll', 'cpp',
   default_options: [
-    'warning_level=3'
+    'warning_level=3',
+    'cpp_std=c++17'
 ])
 
 executable('epoll_server', ['src/main.cpp'])

src/EpollEntry.hpp

 #pragma once
 
-#include <stdint.h>
+#include <cstdint>
+#include <cassert>
+#include <unistd.h>
 #include <sys/epoll.h>
 
 class EpollEntry {
 private:
-    int fd;
-    uint32_t events;
+    /** Events this epoll entry reacts to. */
+    uint32_t events_;
+    /** Indicates if `fd_` should be closed when this epoll entry is destructed. */
+    const bool should_close_fd_;
+protected:
+    /** The file descriptor this epoll entry is polling on. */
+    int fd_;
 
 public:
-    /*! \brief How to react to epoll events?
-     *
-     * Return false if this should be removed from epoll instance.
-     */
-    virtual bool handleEvent(uint32_t events) = 0;
-
-    /*! What file descriptor does this epoll entry wrap? */
-    void set_fd(int i) {
-        fd = i;
+    EpollEntry(int fd, uint32_t events, bool should_close_fd = true)
+            : events_{events}, should_close_fd_{should_close_fd}, fd_{fd} {
+        assert(fd >= 0);
     }
 
-    int get_fd() const {
-        return fd;
+    virtual ~EpollEntry() {
+        if (should_close_fd_) {
+            close(fd_);
+        }
     }
 
-    /*! To what events react? */
-    void set_events(uint32_t i) {
-        events = i;
-    }
+    // we have a file descriptor, prevent copy, allow move
+    EpollEntry(EpollEntry&) = delete;
+    EpollEntry(EpollEntry&&) noexcept = default;
+
+    /** This callback is called by `EpollEventLoop` when the entry is removed. */
+    virtual void on_remove() {}
 
-    uint32_t get_events() const {
-        return events;
+    /**
+     * Invoked when the epoll entry is signalled.
+     * Returns false if this entry should be removed from the invoking `EpollInstance`.
+     */
+    virtual bool handle_event(uint32_t events) = 0;
+
+    [[nodiscard]] int fd() const {
+        return fd_;
     }
 
-    virtual ~EpollEntry() = default;
-};
+    [[nodiscard]] uint32_t events() const {
+        return events_;
+    }
+};
\ No newline at end of file

src/EpollEventLoop.hpp

 #pragma once
 
-#include <stdint.h>
+#include "EpollEntry.hpp"
+#include "error_util.hpp"
+#include <cstddef>
+#include <cstring>
 #include <unistd.h>
+#include <system_error>
 #include <sys/epoll.h>
-#include <cstring>
-#include <stdexcept>
-#include "EpollEntry.hpp"
+#include <array>
 
 class EpollEventLoop {
 public:
     static constexpr size_t MAX_EPOLL_EVENTS = 64;
 private:
-    int fd;
-    bool should_stop = false;
+    int fd_;
+    bool should_stop_ = false;
 
 public:
-    EpollEventLoop() {
-        this->fd = epoll_create1(0);
-        if (this->fd == -1) {
-            throw std::runtime_error(
-                    std::string("epoll_create1: ") + std::strerror(errno));
-        }
-    }
+    EpollEventLoop() : fd_{CHECK_ERROR(epoll_create1(0))} {}
 
     ~EpollEventLoop() {
-        close(this->fd);
+        close(fd_);
     }
 
-    void registerEpollEntry(EpollEntry& e) const {
-        struct epoll_event ev;
-        memset(&ev, 0, sizeof(ev));
+    // we have a file descriptor, prevent copy, allow move
+    EpollEventLoop(EpollEventLoop&) = delete;
+    EpollEventLoop(EpollEventLoop&&) noexcept = default;
 
-        ev.events = e.get_events();
+    /** Add an epoll entry to this epoll instance. */
+    void add(EpollEntry& e) const {
+        epoll_event ev{};
+        ev.events = e.events();
         ev.data.ptr = &e;
-
-        if (epoll_ctl(this->fd, EPOLL_CTL_ADD, e.get_fd(), &ev) == -1) {
-            throw std::runtime_error(
-                    std::string("epoll_ctl: ") + std::strerror(errno));
-        }
+        CHECK_ERROR(epoll_ctl(fd_, EPOLL_CTL_ADD, e.fd(), &ev));
     }
 
-    void unregisterEpollEntry(EpollEntry& e) const {
-        struct epoll_event ev;
-        memset(&ev, 0, sizeof(ev));
-
+    /**
+     * Remove an epoll entry from this epoll instance. Invokes the `on_remove()`
+     * callback of the entry.
+     */
+    void remove(EpollEntry& e) const {
+        epoll_event ev{};
         ev.events = 0;
         ev.data.ptr = &e;
-
-        if (epoll_ctl(this->fd, EPOLL_CTL_DEL, e.get_fd(), &ev) == -1) {
-            throw std::runtime_error(
-                    std::string("epoll_ctl: ") + std::strerror(errno));
-        }
+        CHECK_ERROR(epoll_ctl(fd_, EPOLL_CTL_DEL, e.fd(), &ev));
+        e.on_remove();
     }
 
+    /** Runs the event loop until `.stop()` is called. */
     void run() {
-        should_stop = false;
-        while (!should_stop) {
-            waitAndHandleEvents();
+        should_stop_ = false;
+        while (!should_stop_) {
+            wait_and_handle_events();
         }
     }
 
+    /** Stops the event loop after all currently pending events are processed. */
     void stop() {
-        should_stop = true;
+        should_stop_ = true;
     }
 
 private:
-    void waitAndHandleEvents() const {
-        struct epoll_event events[MAX_EPOLL_EVENTS];
-        int n = epoll_wait(this->fd, events, MAX_EPOLL_EVENTS, -1);
+    void wait_and_handle_events() const {
+        std::array<epoll_event, MAX_EPOLL_EVENTS> events{};
+        int n = CHECK_ERROR_EINTR(epoll_wait(fd_, events.data(), events.size(), -1));
         if (n == -1) {
-            throw std::runtime_error(
-                    std::string("epoll_wait: ") + std::strerror(errno));
+            return; // received a signal
         }
+
         for (int i = 0; i < n; i++) {
-            EpollEntry* e = static_cast<EpollEntry*>(events[i].data.ptr);
-            if (!e->handleEvent(events[i].events)) {
-                this->unregisterEpollEntry(*e);
+            auto* e = static_cast<EpollEntry*>(events[i].data.ptr);
+            if (!e->handle_event(events[i].events)) {
+                remove(*e);
             }
         }
     }
-};
+};
\ No newline at end of file

src/EpollPeriodicTimer.hpp

 #pragma once
 
-#include <stdint.h>
+#include <cstdint>
 #include <cstring>
-#include <iostream>
-#include <stdexcept>
-#include <sys/timerfd.h>
 #include <unistd.h>
+#include <sys/timerfd.h>
+#include <chrono>
+#include <type_traits>
 #include "EpollEntry.hpp"
+#include "error_util.hpp"
 
+template<typename Callback>
 class EpollPeriodicTimer : public EpollEntry {
-public:
-    EpollPeriodicTimer(uint32_t timeMs) {
-        struct itimerspec its;
-        memset(&its, 0, sizeof(its));
-
-        this->set_fd(timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK));
-        if (this->get_fd() == -1) {
-            throw std::runtime_error(
-                    std::string("timerfd_create: ") + std::strerror(errno));
-        }
-
-        its.it_interval.tv_sec = timeMs / 1000;
-        its.it_interval.tv_nsec = (timeMs % 1000) * 1000000;
-        its.it_value.tv_sec = timeMs / 1000;
-        its.it_value.tv_nsec = (timeMs % 1000) * 1000000;
+private:
+    Callback cb_;
 
-        if (timerfd_settime(this->get_fd(), 0, &its, NULL)) {
-            throw std::runtime_error(
-                    std::string("timerfd_settime: ") + std::strerror(errno));
-        }
-
-        this->set_events(EPOLLIN);
-    }
-
-    ~EpollPeriodicTimer() {
-        close(this->get_fd());
+public:
+    /**
+     * @param timeout - timer period
+     * @param cb - callback, invoked whenever the timer expires; it is invoked either
+     * as `cb(expiration_count)` or `cb()`, whichever is supported
+     */
+    EpollPeriodicTimer(std::chrono::nanoseconds timeout, Callback cb)
+            : EpollEntry(CHECK_ERROR(timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK)), EPOLLIN),
+              cb_{cb} {
+        using namespace std::chrono;
+
+        // set up the timerfd interval
+        itimerspec its{};
+        auto sec_part = duration_cast<seconds>(timeout);
+        its.it_interval.tv_sec = sec_part.count();
+        its.it_interval.tv_nsec = nanoseconds(timeout - sec_part).count();
+        its.it_value = its.it_interval;
+        CHECK_ERROR(timerfd_settime(fd_, 0, &its, nullptr));
     }
 
-    bool handleEvent(uint32_t events) {
-        uint64_t value;
+    bool handle_event(uint32_t events) override {
         if ((events & EPOLLERR) || (events & EPOLLHUP) || !(events & EPOLLIN)) {
             return false;
         } else {
-            auto len = read(this->get_fd(), &value, 8);
-            (void)len;
-            std::cout << "timer: " << this->get_fd() << std::endl;
+            uint64_t expiration_count;
+            check_error("timerfd read", read(fd_, &expiration_count, 8));
+            // support lambda without arguments
+            if constexpr (std::is_invocable_v<Callback, uint64_t>) {
+                cb_(expiration_count);
+            } else {
+                cb_();
+            }
             return true;
         }
     }
-};
+};
\ No newline at end of file

src/EpollStdInLine.hpp

 #pragma once
 
-#include <stdint.h>
-#include <iostream>
-#include <unistd.h>
-#include <string>
 #include "EpollEntry.hpp"
+#include <iostream>
 
+template<typename Callback>
 class EpollStdInLine : public EpollEntry {
+private:
+    Callback cb_;
+
 public:
-    EpollStdInLine() {
-        this->set_fd(STDIN_FILENO);
-        this->set_events(EPOLLIN);
-    }
+    explicit EpollStdInLine(Callback cb) : EpollEntry(STDIN_FILENO, EPOLLIN, false), cb_{cb} {}
 
-    bool handleEvent(uint32_t events) {
-        std::string line;
+    bool handle_event(uint32_t events) override {
         if ((events & EPOLLERR) || (events & EPOLLHUP) || !(events & EPOLLIN)) {
             return false;
         } else {
+            std::string line;
             std::getline(std::cin, line);
-            std::cout << "stdin line: " << line << std::endl;
+            cb_(line);
             return true;
         }
     }
-};
+};
\ No newline at end of file

src/error_util.hpp

+#pragma once
+
+#include <system_error>
+#include <cerrno>
+#include <string>
+
+static inline std::system_error system_error_from_errno(const std::string& fn) {
+    throw std::system_error(std::error_code(errno, std::system_category()), fn);
+}
+
+template<typename T>
+static inline T check_error(const std::string& fn, T return_value, bool allow_eintr = false) {
+    if (return_value == -1 && (!allow_eintr || errno != EINTR)) {
+        throw system_error_from_errno(fn);
+    }
+    return return_value;
+}
+
+#define CHECK_ERROR(fn) check_error(#fn, fn)
+#define CHECK_ERROR_EINTR(fn) check_error(#fn, fn, true)
\ No newline at end of file

src/main.cpp

 #include "EpollEventLoop.hpp"
 #include "EpollStdInLine.hpp"
 #include "EpollPeriodicTimer.hpp"
+#include <iostream>
 
 int main() {
-    EpollEventLoop ep{};
-    EpollPeriodicTimer tim1{1000};
-    EpollPeriodicTimer tim2{1500};
-    EpollStdInLine sin{};
+    EpollEventLoop loop{};
 
-    ep.registerEpollEntry(tim1);
-    ep.registerEpollEntry(tim2);
-    ep.registerEpollEntry(sin);
+    using namespace std::chrono_literals;
+    EpollPeriodicTimer tim1(1000ms, [&] { std::cout << "timer: 4" << std::endl; });
+    EpollPeriodicTimer tim2(1500ms, [&] { std::cout << "timer: 5" << std::endl; });
+    EpollStdInLine sin([&](const std::string& line) {
+        std::cout << "stdin: " << line << std::endl;
+    });
 
-    ep.run();
+    loop.add(sin);
+    loop.add(tim1);
+    loop.add(tim2);
 
-    ep.unregisterEpollEntry(tim1);
-    ep.unregisterEpollEntry(tim2);
-    ep.unregisterEpollEntry(sin);
+    loop.run();
+
+    loop.remove(tim2);
+    loop.remove(tim1);
+    loop.remove(sin);
 
     return 0;
 }