From 0824ba7e23a92180cb203445bdff0fc63b776b9b Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Mon, 9 Oct 2023 22:00:15 +0200
Subject: [PATCH] libos: Add timers to event loops

Only second precision for now, as alarm() is used to control the timers. Hopefully setitimer() or timer_create() can be added to the kernel soon to benefit from more precision.
---
 libos/include/os/EventLoop.h | 24 +++++++++++++++++
 libos/src/EventLoop.cpp      | 51 ++++++++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+)

diff --git a/libos/include/os/EventLoop.h b/libos/include/os/EventLoop.h
index e48b9ff8..ea56c2b4 100644
--- a/libos/include/os/EventLoop.h
+++ b/libos/include/os/EventLoop.h
@@ -9,7 +9,9 @@
 
 #pragma once
 #include <luna/HashMap.h>
+#include <luna/LinkedList.h>
 #include <luna/Vector.h>
+#include <os/Action.h>
 #include <sys/poll.h>
 
 namespace os
@@ -52,9 +54,22 @@ namespace os
          *
          * Unlike standard POSIX signal handling, this handler will be run synchronously as part of the event loop,
          * eliminating many problems with asynchronous signal handling.
+         *
+         * @param sig The signal to handle.
+         * @param handler The function to call when this signal is caught.
+         * @return Result<void> Whether the operation succeeded.
          */
         Result<void> register_signal_handler(int sig, void (*handler)(int));
 
+        /**
+         * @brief Register a function to be called in a certain amount of time.
+         *
+         * @param seconds The number of seconds to wait before invoking the function.
+         * @param callback The function to call when the time is up.
+         * @return Result<void> Whether the operation succeeded.
+         */
+        Result<void> register_timer(unsigned int seconds, Action&& callback);
+
         /**
          * @brief Run the event loop until it is asked to quit.
          *
@@ -76,10 +91,19 @@ namespace os
 
         static void handle_signal(int sig);
         static void handle_quit_signal(int);
+        static void handle_timer_signal(int);
 
         bool m_should_quit { false };
         int m_quit_status { 0 };
 
         int m_signal_pipe[2];
+
+        struct Timer final : public LinkedListNode<Timer>
+        {
+            long target;
+            Action action;
+        };
+
+        LinkedList<Timer> m_timer_queue;
     };
 }
diff --git a/libos/src/EventLoop.cpp b/libos/src/EventLoop.cpp
index 43655f8c..5fe31d5d 100644
--- a/libos/src/EventLoop.cpp
+++ b/libos/src/EventLoop.cpp
@@ -12,6 +12,7 @@
 #include <os/File.h>
 #include <signal.h>
 #include <string.h>
+#include <time.h>
 #include <unistd.h>
 
 static os::EventLoop* s_the = nullptr;
@@ -28,6 +29,7 @@ namespace os
 
         register_signal_handler(SIGTERM, EventLoop::handle_quit_signal).release_value();
         register_signal_handler(SIGINT, EventLoop::handle_quit_signal).release_value();
+        register_signal_handler(SIGALRM, EventLoop::handle_timer_signal).release_value();
     }
 
     EventLoop::~EventLoop()
@@ -60,6 +62,40 @@ namespace os
         return {};
     }
 
+    Result<void> EventLoop::register_timer(unsigned int seconds, Action&& callback)
+    {
+        long target = time(NULL) + seconds;
+
+        auto* timer = TRY(make<Timer>());
+        timer->target = target;
+        timer->action = move(callback);
+
+        Timer* next = nullptr;
+
+        for (auto* t : m_timer_queue)
+        {
+            if (target < t->target)
+            {
+                next = t;
+                break;
+            }
+        }
+
+        if (m_timer_queue.first().value_or(nullptr) == next)
+        {
+            alarm(seconds);
+            m_timer_queue.prepend(timer);
+        }
+        else if (next == nullptr) { m_timer_queue.append(timer); }
+        else
+        {
+            auto previous = m_timer_queue.previous(next).value();
+            m_timer_queue.add_after(previous, timer);
+        }
+
+        return {};
+    }
+
     int EventLoop::run()
     {
         while (!m_should_quit)
@@ -113,4 +149,19 @@ namespace os
         os::println("EventLoop: quit requested by signal %d", sig);
         the().quit(sig);
     }
+
+    void EventLoop::handle_timer_signal(int)
+    {
+        auto& queue = the().m_timer_queue;
+        if (queue.count())
+        {
+            auto timer = queue.remove(queue.expect_first());
+
+            auto first = queue.first();
+            if (first.has_value()) { alarm((unsigned int)(first.value()->target - time(NULL))); }
+
+            timer->action();
+            delete timer;
+        }
+    }
 }