From 8a57d8a9b755ffb83aedb350dfc38745fc59e2e7 Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Thu, 16 Nov 2023 21:58:45 +0100
Subject: [PATCH] libos: Use setitimer() for millisecond precision

---
 apps/clock.cpp               |  2 +-
 libos/include/os/EventLoop.h |  4 ++--
 libos/src/EventLoop.cpp      | 27 +++++++++++++++++++++++----
 3 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/apps/clock.cpp b/apps/clock.cpp
index b63b3dae..080958b3 100644
--- a/apps/clock.cpp
+++ b/apps/clock.cpp
@@ -14,7 +14,7 @@ void update_time()
 
     g_label->set_text(StringView { buf });
 
-    os::EventLoop::the().register_timer(1, update_time);
+    os::EventLoop::the().register_timer(1000, update_time);
 
     ui::App::the().main_window()->draw();
 }
diff --git a/libos/include/os/EventLoop.h b/libos/include/os/EventLoop.h
index ea56c2b4..6eb6a9e5 100644
--- a/libos/include/os/EventLoop.h
+++ b/libos/include/os/EventLoop.h
@@ -64,11 +64,11 @@ namespace os
         /**
          * @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 milliseconds The number of milliseconds 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);
+        Result<void> register_timer(long milliseconds, Action&& callback);
 
         /**
          * @brief Run the event loop until it is asked to quit.
diff --git a/libos/src/EventLoop.cpp b/libos/src/EventLoop.cpp
index 5fe31d5d..c699c1c6 100644
--- a/libos/src/EventLoop.cpp
+++ b/libos/src/EventLoop.cpp
@@ -12,11 +12,27 @@
 #include <os/File.h>
 #include <signal.h>
 #include <string.h>
+#include <sys/time.h>
 #include <time.h>
 #include <unistd.h>
 
 static os::EventLoop* s_the = nullptr;
 
+static void alarm_milliseconds(long target)
+{
+    struct itimerval itimer;
+    memset(&itimer.it_interval, 0, sizeof(itimer.it_interval));
+    itimer.it_value = { .tv_sec = target / 1000, .tv_usec = (target % 1000) * 1000 };
+    setitimer(ITIMER_REAL, &itimer, nullptr);
+}
+
+static long get_monotonic_time_in_milliseconds()
+{
+    struct timespec time;
+    clock_gettime(CLOCK_MONOTONIC, &time);
+    return time.tv_sec * 1000 + time.tv_nsec / 1'000'000;
+}
+
 namespace os
 {
     EventLoop::EventLoop()
@@ -62,9 +78,9 @@ namespace os
         return {};
     }
 
-    Result<void> EventLoop::register_timer(unsigned int seconds, Action&& callback)
+    Result<void> EventLoop::register_timer(long milliseconds, Action&& callback)
     {
-        long target = time(NULL) + seconds;
+        long target = get_monotonic_time_in_milliseconds() + milliseconds;
 
         auto* timer = TRY(make<Timer>());
         timer->target = target;
@@ -83,7 +99,7 @@ namespace os
 
         if (m_timer_queue.first().value_or(nullptr) == next)
         {
-            alarm(seconds);
+            alarm_milliseconds(milliseconds);
             m_timer_queue.prepend(timer);
         }
         else if (next == nullptr) { m_timer_queue.append(timer); }
@@ -158,7 +174,10 @@ namespace os
             auto timer = queue.remove(queue.expect_first());
 
             auto first = queue.first();
-            if (first.has_value()) { alarm((unsigned int)(first.value()->target - time(NULL))); }
+            if (first.has_value())
+            {
+                alarm((unsigned int)(first.value()->target - get_monotonic_time_in_milliseconds()));
+            }
 
             timer->action();
             delete timer;