fix: Use QueryPerformanceCounter on windows for monotonic time.

This fixes time resolution issues and simplifies the code a bit. QPC can
in theory jump forward in time, but in practice not by enough to matter
in our use case.

Author: iphydf

auto_tests/auto_test_support.c

@@ -149,6 +149,8 @@ void set_mono_time_callback(AutoTox *autotox)
     Mono_Time *mono_time = autotox->tox->mono_time;
 
     autotox->clock = current_time_monotonic(mono_time);
+    ck_assert_msg(autotox->clock >= 1000,
+                  "clock is too low (not initialised?): %lu", (unsigned long)autotox->clock);
     mono_time_set_current_time_callback(mono_time, nullptr, nullptr);  // set to default first
     mono_time_set_current_time_callback(mono_time, get_state_clock_callback, &autotox->clock);
 }

toxcore/group_announce_test.cc

@@ -9,7 +9,7 @@ namespace {
 struct Announces : ::testing::Test {
 protected:
     const Memory *mem_ = system_memory();
-    uint64_t clock_ = 0;
+    uint64_t clock_ = 1000;
     Mono_Time *mono_time_ = nullptr;
     GC_Announces_List *gca_ = nullptr;
     GC_Announce _ann1;

toxcore/mono_time.c

@@ -1,5 +1,5 @@
 /* SPDX-License-Identifier: GPL-3.0-or-later
- * Copyright © 2016-2020 The TokTok team.
+ * Copyright © 2016-2023 The TokTok team.
  * Copyright © 2014 Tox project.
  */
 #ifndef _XOPEN_SOURCE
@@ -40,12 +40,6 @@
 struct Mono_Time {
     uint64_t cur_time;
     uint64_t base_time;
-#ifdef OS_WIN32
-    /* protect `last_clock_update` and `last_clock_mono` from concurrent access */
-    pthread_mutex_t last_clock_lock;
-    uint32_t last_clock_mono;
-    bool last_clock_update;
-#endif
 
 #ifndef ESP_PLATFORM
     /* protect `time` from concurrent access */
@@ -56,42 +50,33 @@ struct Mono_Time {
     void *user_data;
 };
 
+static uint64_t timespec_to_u64(struct timespec clock_mono)
+{
+    return UINT64_C(1000) * clock_mono.tv_sec + (clock_mono.tv_nsec / UINT64_C(1000000));
+}
+
 #ifdef OS_WIN32
 non_null()
 static uint64_t current_time_monotonic_default(void *user_data)
 {
-    Mono_Time *const mono_time = (Mono_Time *)user_data;
-
-    /* Must hold mono_time->last_clock_lock here */
-
-    /* GetTickCount provides only a 32 bit counter, but we can't use
-     * GetTickCount64 for backwards compatibility, so we handle wraparound
-     * ourselves.
-     */
-    const uint32_t ticks = GetTickCount();
-
-    /* the higher 32 bits count the number of wrap arounds */
-    uint64_t old_ovf = mono_time->cur_time & ~((uint64_t)UINT32_MAX);
-
-    /* Check if time has decreased because of 32 bit wrap from GetTickCount() */
-    if (ticks < mono_time->last_clock_mono) {
-        /* account for overflow */
-        old_ovf += UINT32_MAX + UINT64_C(1);
+    LARGE_INTEGER freq;
+    LARGE_INTEGER count;
+    if (!QueryPerformanceFrequency(&freq)) {
+        return 0;
     }
-
-    if (mono_time->last_clock_update) {
-        mono_time->last_clock_mono = ticks;
-        mono_time->last_clock_update = false;
+    if (!QueryPerformanceCounter(&count)) {
+        return 0;
     }
-
-    /* splice the low and high bits back together */
-    return old_ovf + ticks;
-}
-#else // !OS_WIN32
-static uint64_t timespec_to_u64(struct timespec clock_mono)
-{
-    return 1000ULL * clock_mono.tv_sec + (clock_mono.tv_nsec / 1000000ULL);
+    struct timespec sp = {0};
+    sp.tv_sec = count.QuadPart / freq.QuadPart;
+    if (freq.QuadPart < 1000000000) {
+        sp.tv_nsec = (count.QuadPart % freq.QuadPart) * 1000000000 / freq.QuadPart;
+    } else {
+        sp.tv_nsec = (long)((count.QuadPart % freq.QuadPart) * (1000000000.0 / freq.QuadPart));
+    }
+    return timespec_to_u64(sp);
 }
+#else
 #ifdef __APPLE__
 non_null()
 static uint64_t current_time_monotonic_default(void *user_data)
@@ -150,27 +135,14 @@ Mono_Time *mono_time_new(const Memory *mem, mono_time_current_time_cb *current_t
 
     mono_time_set_current_time_callback(mono_time, current_time_callback, user_data);
 
-#ifdef OS_WIN32
-
-    mono_time->last_clock_mono = 0;
-    mono_time->last_clock_update = false;
-
-    if (pthread_mutex_init(&mono_time->last_clock_lock, nullptr) < 0) {
-        mem_delete(mem, mono_time->time_update_lock);
-        mem_delete(mem, mono_time);
-        return nullptr;
-    }
-
-#endif
-
     mono_time->cur_time = 0;
 #ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
     // Maximum reproducibility. Never return time = 0.
     mono_time->base_time = 1;
 #else
     // Never return time = 0 in case time() returns 0 (e.g. on microcontrollers
     // without battery-powered RTC or ones where NTP didn't initialise it yet).
-    mono_time->base_time = max_u64(1, (uint64_t)time(nullptr)) * 1000ULL - current_time_monotonic(mono_time);
+    mono_time->base_time = max_u64(1, (uint64_t)time(nullptr)) * UINT64_C(1000) - current_time_monotonic(mono_time);
 #endif
 
     mono_time_update(mono_time);
@@ -183,9 +155,6 @@ void mono_time_free(const Memory *mem, Mono_Time *mono_time)
     if (mono_time == nullptr) {
         return;
     }
-#ifdef OS_WIN32
-    pthread_mutex_destroy(&mono_time->last_clock_lock);
-#endif
 #ifndef ESP_PLATFORM
     pthread_rwlock_destroy(mono_time->time_update_lock);
     mem_delete(mem, mono_time->time_update_lock);
@@ -195,16 +164,8 @@ void mono_time_free(const Memory *mem, Mono_Time *mono_time)
 
 void mono_time_update(Mono_Time *mono_time)
 {
-#ifdef OS_WIN32
-    /* we actually want to update the overflow state of mono_time here */
-    pthread_mutex_lock(&mono_time->last_clock_lock);
-    mono_time->last_clock_update = true;
-#endif
     const uint64_t cur_time =
         mono_time->base_time + mono_time->current_time_callback(mono_time->user_data);
-#ifdef OS_WIN32
-    pthread_mutex_unlock(&mono_time->last_clock_lock);
-#endif
 
 #ifndef ESP_PLATFORM
     pthread_rwlock_wrlock(mono_time->time_update_lock);
@@ -230,7 +191,7 @@ uint64_t mono_time_get_ms(const Mono_Time *mono_time)
 
 uint64_t mono_time_get(const Mono_Time *mono_time)
 {
-    return mono_time_get_ms(mono_time) / 1000ULL;
+    return mono_time_get_ms(mono_time) / UINT64_C(1000);
 }
 
 bool mono_time_is_timeout(const Mono_Time *mono_time, uint64_t timestamp, uint64_t timeout)
@@ -257,15 +218,5 @@ void mono_time_set_current_time_callback(Mono_Time *mono_time,
  */
 uint64_t current_time_monotonic(Mono_Time *mono_time)
 {
-    /* For WIN32 we don't want to change overflow state of mono_time here */
-#ifdef OS_WIN32
-    /* We don't want to update the overflow state of mono_time here,
-     * but must protect against other threads */
-    pthread_mutex_lock(&mono_time->last_clock_lock);
-#endif
-    const uint64_t cur_time = mono_time->current_time_callback(mono_time->user_data);
-#ifdef OS_WIN32
-    pthread_mutex_unlock(&mono_time->last_clock_lock);
-#endif
-    return cur_time;
+    return mono_time->current_time_callback(mono_time->user_data);
 }

toxcore/mono_time_test.cc

@@ -53,11 +53,14 @@ TEST(MonoTime, IsTimeoutReal)
     uint64_t const start = mono_time_get(mono_time);
     EXPECT_FALSE(mono_time_is_timeout(mono_time, start, 5));
 
+    const uint64_t before_sleep = mono_time_get(mono_time);
     std::this_thread::sleep_for(std::chrono::milliseconds(100));
     mono_time_update(mono_time);
+    const uint64_t after_sleep = mono_time_get(mono_time);
 
     // should still not have timed out (5sec) after sleeping ~100ms
-    EXPECT_FALSE(mono_time_is_timeout(mono_time, start, 5));
+    EXPECT_FALSE(mono_time_is_timeout(mono_time, start, 5))
+        << "before sleep: " << before_sleep << ", after sleep: " << after_sleep;
 
     mono_time_free(mem, mono_time);
 }