[Spice-devel] [PATCH spice-gtk] spice-gtk: Use time comparisons that still work after wraparound

[Christophe de Dinechin]

From: Christophe de Dinechin <dinechin at redhat.com>

The mm timer is a millisecond timer that wraps around after ~49 days.
All comparisons that look like a<b will fail once this happens.
Instead, use signed ((int)(a-b)<0), which may fail if there is more than
25 days between a and b (should not be happening under normal conditions),
but is robust to the timer wrapping around.

Signed-off-by: Christophe de Dinechin <dinechin at redhat.com>
---
 src/channel-display-gst.c   | 4 ++--
 src/channel-display-mjpeg.c | 4 ++--
 src/channel-display.c       | 2 +-
 src/channel-playback.c      | 2 +-
 src/spice-channel-priv.h    | 5 +++++
 src/spice-session.c         | 4 ++--
 6 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/src/channel-display-gst.c b/src/channel-display-gst.c
index 3cf451b..495036f 100644
--- a/src/channel-display-gst.c
+++ b/src/channel-display-gst.c
@@ -166,7 +166,7 @@ static void schedule_frame(SpiceGstDecoder *decoder)
             break;
         }
 
-        if (now < gstframe->frame->mm_time) {
+        if (spice_mm_strictly_before(now, gstframe->frame->mm_time)) {
             decoder->timer_id = g_timeout_add(gstframe->frame->mm_time - now,
                                               display_frame, decoder);
         } else if (g_queue_get_length(decoder->display_queue) == 1) {
@@ -509,7 +509,7 @@ static gboolean spice_gst_decoder_queue_frame(VideoDecoder *video_decoder,
         return TRUE;
     }
 
-    if (frame->mm_time < decoder->last_mm_time) {
+    if (spice_mm_strictly_before(frame->mm_time, decoder->last_mm_time)) {
         SPICE_DEBUG("new-frame-time < last-frame-time (%u < %u):"
                     " resetting stream",
                     frame->mm_time, decoder->last_mm_time);
diff --git a/src/channel-display-mjpeg.c b/src/channel-display-mjpeg.c
index ee33b01..c91fa53 100644
--- a/src/channel-display-mjpeg.c
+++ b/src/channel-display-mjpeg.c
@@ -201,7 +201,7 @@ static void mjpeg_decoder_schedule(MJpegDecoder *decoder)
     decoder->cur_frame = NULL;
     do {
         if (frame) {
-            if (time <= frame->mm_time) {
+            if (spice_mm_before(time, frame->mm_time)) {
                 guint32 d = frame->mm_time - time;
                 decoder->cur_frame = frame;
                 decoder->timer_id = g_timeout_add(d, mjpeg_decoder_decode_frame, decoder);
@@ -251,7 +251,7 @@ static gboolean mjpeg_decoder_queue_frame(VideoDecoder *video_decoder,
 
     last_frame = g_queue_peek_tail(decoder->msgq);
     if (last_frame) {
-        if (frame->mm_time < last_frame->mm_time) {
+        if (spice_mm_strictly_before(frame->mm_time, last_frame->mm_time)) {
             /* This should really not happen */
             SPICE_DEBUG("new-frame-time < last-frame-time (%u < %u):"
                         " resetting stream",
diff --git a/src/channel-display.c b/src/channel-display.c
index 3c98d79..fe7506e 100644
--- a/src/channel-display.c
+++ b/src/channel-display.c
@@ -1366,7 +1366,7 @@ static void display_update_stream_report(SpiceDisplayChannel *channel, uint32_t
     }
 
     if (st->report_num_frames >= st->report_max_window ||
-        now - st->report_start_time >= st->report_timeout ||
+        spice_mm_after(now - st->report_start_time, st->report_timeout) ||
         st->report_drops_seq_len >= STREAM_REPORT_DROP_SEQ_LEN_LIMIT) {
         SpiceMsgcDisplayStreamReport report;
         SpiceSession *session = spice_channel_get_session(SPICE_CHANNEL(channel));
diff --git a/src/channel-playback.c b/src/channel-playback.c
index ca14b96..451dfaf 100644
--- a/src/channel-playback.c
+++ b/src/channel-playback.c
@@ -313,7 +313,7 @@ static void playback_handle_data(SpiceChannel *channel, SpiceMsgIn *in)
                   packet->time, packet->data, packet->data_size);
 #endif
 
-    if (c->last_time > packet->time)
+    if (spice_mm_strictly_after(c->last_time, packet->time))
         g_warn_if_reached();
 
     c->last_time = packet->time;
diff --git a/src/spice-channel-priv.h b/src/spice-channel-priv.h
index 7288920..b896aaa 100644
--- a/src/spice-channel-priv.h
+++ b/src/spice-channel-priv.h
@@ -43,6 +43,11 @@ G_BEGIN_DECLS
 #define CHANNEL_DEBUG(channel, fmt, ...) \
     SPICE_DEBUG("%s: " fmt, SPICE_CHANNEL(channel)->priv->name, ## __VA_ARGS__)
 
+#define spice_mm_after(now, time)               ((int32_t) ((now)-(time)) >= 0)
+#define spice_mm_before(now, time)              ((int32_t) ((now)-(time)) <= 0)
+#define spice_mm_strictly_after(now, time)      ((int32_t) ((now)-(time)) > 0)
+#define spice_mm_strictly_before(now, time)     ((int32_t) ((now)-(time)) < 0)
+
 struct _SpiceMsgOut {
     int                   refcount;
     SpiceChannel          *channel;
diff --git a/src/spice-session.c b/src/spice-session.c
index 6f8cf5e..62b041e 100644
--- a/src/spice-session.c
+++ b/src/spice-session.c
@@ -2336,8 +2336,8 @@ void spice_session_set_mm_time(SpiceSession *session, guint32 time)
     s->mm_time = time;
     s->mm_time_at_clock = g_get_monotonic_time();
     SPICE_DEBUG("set mm time: %u", spice_session_get_mm_time(session));
-    if (time > old_time + MM_TIME_DIFF_RESET_THRESH ||
-        time < old_time) {
+    if (spice_mm_strictly_after(time, old_time + MM_TIME_DIFF_RESET_THRESH) ||
+        spice_mm_strictly_before(time, old_time)) {
         SPICE_DEBUG("%s: mm-time-reset, old %u, new %u", __FUNCTION__, old_time, s->mm_time);
         g_coroutine_signal_emit(session, signals[SPICE_SESSION_MM_TIME_RESET], 0);
     }
-- 
2.11.0 (Apple Git-81)