unix: update loop->time after poll

Fixes a bug where timers expire prematurely when the following
conditions hold:

  a) libuv first spends some time blocked in the platform poll function
  b) a callback then calls uv_timer_start()

Cause: uv_timer_start() uses an out-of-date loop->time in its
'when should the timer callback run?' calculations.

Solution: Update loop->time before invoking any callbacks.

Fixes #678.

src/unix/core.c

@@ -286,7 +286,7 @@ int uv_run2(uv_loop_t* loop, uv_run_mode mode) {
     return 0;
 
   do {
-    uv_update_time(loop);
+    uv__update_time(loop);
     uv__run_timers(loop);
     uv__run_idle(loop);
     uv__run_prepare(loop);
@@ -307,7 +307,7 @@ int uv_run(uv_loop_t* loop) {
 
 
 void uv_update_time(uv_loop_t* loop) {
-  loop->time = uv__hrtime() / 1000000;
+  uv__update_time(loop);
 }
 
 

src/unix/internal.h

@@ -105,14 +105,6 @@ enum {
   UV_TCP_SINGLE_ACCEPT = 0x400  /* Only accept() when idle. */
 };
 
-__attribute__((unused))
-static void uv__req_init(uv_loop_t* loop, uv_req_t* req, uv_req_type type) {
-  req->type = type;
-  uv__req_register(loop, req);
-}
-#define uv__req_init(loop, req, type) \
-  uv__req_init((loop), (uv_req_t*)(req), (type))
-
 /* core */
 void uv__handle_init(uv_loop_t* loop, uv_handle_t* handle, uv_handle_type type);
 int uv__nonblock(int fd, int set);
@@ -238,4 +230,17 @@ static const int kFSEventStreamEventFlagItemIsSymlink = 0x00040000;
 
 #endif /* defined(__APPLE__) */
 
+__attribute__((unused))
+static void uv__req_init(uv_loop_t* loop, uv_req_t* req, uv_req_type type) {
+  req->type = type;
+  uv__req_register(loop, req);
+}
+#define uv__req_init(loop, req, type) \
+  uv__req_init((loop), (uv_req_t*)(req), (type))
+
+__attribute__((unused))
+static void uv__update_time(uv_loop_t* loop) {
+  loop->time = uv__hrtime() / 1000000;
+}
+
 #endif /* UV_UNIX_INTERNAL_H_ */

src/unix/kqueue.c

@@ -141,6 +141,12 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
                   ARRAY_SIZE(events),
                   timeout == -1 ? NULL : &spec);
 
+    /* Update loop->time unconditionally. It's tempting to skip the update when
+     * timeout == 0 (i.e. non-blocking poll) but there is no guarantee that the
+     * operating system didn't reschedule our process while in the syscall.
+     */
+    SAVE_ERRNO(uv__update_time(loop));
+
     if (nfds == 0) {
       assert(timeout != -1);
       return;
@@ -244,10 +250,7 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
 update_timeout:
     assert(timeout > 0);
 
-    diff = uv__hrtime() / 1000000;
-    assert(diff >= base);
-    diff -= base;
-
+    diff = loop->time - base;
     if (diff >= (uint64_t) timeout)
       return;
 

src/unix/linux/linux-core.c

@@ -182,6 +182,12 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
                           ARRAY_SIZE(events),
                           timeout);
 
+    /* Update loop->time unconditionally. It's tempting to skip the update when
+     * timeout == 0 (i.e. non-blocking poll) but there is no guarantee that the
+     * operating system didn't reschedule our process while in the syscall.
+     */
+    SAVE_ERRNO(uv__update_time(loop));
+
     if (nfds == 0) {
       assert(timeout != -1);
       return;
@@ -243,10 +249,7 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
 update_timeout:
     assert(timeout > 0);
 
-    diff = uv__hrtime() / 1000000;
-    assert(diff >= base);
-    diff -= base;
-
+    diff = loop->time - base;
     if (diff >= (uint64_t) timeout)
       return;
 

src/unix/sunos.c

@@ -150,6 +150,12 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
         abort();
     }
 
+    /* Update loop->time unconditionally. It's tempting to skip the update when
+     * timeout == 0 (i.e. non-blocking poll) but there is no guarantee that the
+     * operating system didn't reschedule our process while in the syscall.
+     */
+    SAVE_ERRNO(uv__update_time(loop));
+
     if (events[0].portev_source == 0) {
       if (timeout == 0)
         return;
@@ -211,10 +217,7 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
 update_timeout:
     assert(timeout > 0);
 
-    diff = uv__hrtime() / 1000000;
-    assert(diff >= base);
-    diff -= base;
-
+    diff = loop->time - base;
     if (diff >= (uint64_t) timeout)
       return;