[PATCH 1/2] server: Convert to and use a timespec directly for timeouts if supported.

[William Horvath]

From: William Horvath

Instead of first converting to milliseconds, then back to a nanosecond-precision
timespec.

This mitigates a side effect of the global current_time and monotonic_time
being updated on every server call's timeout, where the end time of any unrelated
server call is moved into the future (depending on the frequency of server calls).

By using a more granular timeout, the overall frequency of server calls doesn't have
as great of an effect on each individual timeout, as we don't have to wait for an
entire millisecond (which was due to the ceiling operation in get_next_timeout).

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=57849
---
 server/fd.c | 76 +++++++++++++++++++++++++++++------------------------
 1 file changed, 42 insertions(+), 34 deletions(-)

diff --git a/server/fd.c b/server/fd.c
index ce32e7f8397..46217dbdd77 100644
--- a/server/fd.c
+++ b/server/fd.c
@@ -662,27 +662,22 @@ static inline void remove_epoll_user( struct fd *fd, int user )

static inline void main_loop_epoll(void)
 {
-    int i, ret, timeout;
+    int i, ret;
+    BOOL infinite;
+    struct timespec ts;
     struct kevent events[128];

if (kqueue_fd == -1) return;

while (active_users)
     {
-        timeout = get_next_timeout();
+        infinite = !get_next_timeout_ts( &ts );

if (!active_users) break;  /* last user removed by a timeout */
         if (kqueue_fd == -1) break;  /* an error occurred with kqueue */

-        if (timeout != -1)
-        {
-            struct timespec ts;
-
-            ts.tv_sec = timeout / 1000;
-            ts.tv_nsec = (timeout % 1000) * 1000000;
-            ret = kevent( kqueue_fd, NULL, 0, events, ARRAY_SIZE( events ), &ts );
-        }
-        else ret = kevent( kqueue_fd, NULL, 0, events, ARRAY_SIZE( events ), NULL );
+        if (infinite) ret = kevent( kqueue_fd, NULL, 0, events, ARRAY_SIZE( events ), NULL );
+        else ret = kevent( kqueue_fd, NULL, 0, events, ARRAY_SIZE( events ), &ts );

set_current_time();

@@ -764,28 +759,24 @@ static inline void remove_epoll_user( struct fd *fd, int user )

static inline void main_loop_epoll(void)
 {
-    int i, nget, ret, timeout;
+    BOOL infinite;
+    int i, nget, ret;
+    struct timespec ts;
     port_event_t events[128];

if (port_fd == -1) return;

while (active_users)
     {
-        timeout = get_next_timeout();
+        infinite = !get_next_timeout_ts( &ts );
+
         nget = 1;

if (!active_users) break;  /* last user removed by a timeout */
         if (port_fd == -1) break;  /* an error occurred with event completion */

-        if (timeout != -1)
-        {
-            struct timespec ts;
-
-            ts.tv_sec = timeout / 1000;
-            ts.tv_nsec = (timeout % 1000) * 1000000;
-            ret = port_getn( port_fd, events, ARRAY_SIZE( events ), &nget, &ts );
-        }
-        else ret = port_getn( port_fd, events, ARRAY_SIZE( events ), &nget, NULL );
+        if (infinite) ret = port_getn( port_fd, events, ARRAY_SIZE( events ), &nget, NULL );
+        else ret = port_getn( port_fd, events, ARRAY_SIZE( events ), &nget, &ts );

if (ret == -1) break;  /* an error occurred with event completion */

@@ -876,10 +867,11 @@ static void remove_poll_user( struct fd *fd, int user )
     active_users--;
 }

-/* process pending timeouts and return the time until the next timeout, in milliseconds */
-static int get_next_timeout(void)
+/* process pending timeouts and return the time until the next timeout with nanosecond precision
+ * returns FALSE to signal infinite timeouts, TRUE otherwise */
+static BOOL get_next_timeout_ts( struct timespec *ts )
 {
-    int ret = user_shared_data ? user_shared_data_timeout : -1;
+    timeout_t next_timeout = user_shared_data ? user_shared_data_timeout : -1;

if (!list_empty( &abs_timeout_list ) || !list_empty( &rel_timeout_list ))
     {
@@ -924,22 +916,38 @@ static int get_next_timeout(void)
         if ((ptr = list_head( &abs_timeout_list )) != NULL)
         {
             struct timeout_user *timeout = LIST_ENTRY( ptr, struct timeout_user, entry );
-            timeout_t diff = (timeout->when - current_time + 9999) / 10000;
-            if (diff > INT_MAX) diff = INT_MAX;
-            else if (diff < 0) diff = 0;
-            if (ret == -1 || diff < ret) ret = diff;
+            timeout_t diff = timeout->when - current_time;
+            if (diff < 0) diff = 0;
+            if (next_timeout == -1 || diff < next_timeout) next_timeout = diff;
         }

if ((ptr = list_head( &rel_timeout_list )) != NULL)
         {
             struct timeout_user *timeout = LIST_ENTRY( ptr, struct timeout_user, entry );
-            timeout_t diff = (-timeout->when - monotonic_time + 9999) / 10000;
-            if (diff > INT_MAX) diff = INT_MAX;
-            else if (diff < 0) diff = 0;
-            if (ret == -1 || diff < ret) ret = diff;
+            timeout_t diff = -timeout->when - monotonic_time;
+            if (diff < 0) diff = 0;
+            if (next_timeout == -1 || diff < next_timeout) next_timeout = diff;
         }
     }
-    return ret;
+
+    /* infinite */
+    if (next_timeout == -1) return FALSE;
+
+    ts->tv_sec = next_timeout / 10000000;
+    ts->tv_nsec = (next_timeout % 10000000) * 100;
+    return TRUE;
+}
+
+/* process pending timeouts and return the time until the next timeout, in milliseconds */
+static int get_next_timeout(void)
+{
+    struct timespec ts;
+
+    if (!get_next_timeout_ts( &ts )) return -1;
+    if (ts.tv_sec >= INT_MAX / 1000) return INT_MAX;
+
+    /* ceil to avoid spinning */
+    return ts.tv_sec * 1000 + (ts.tv_nsec + 999999) / 1000000;
 }

/* server main poll() loop */