Precise timouts in zmq_poll implemented

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/zmq.cpp

@@ -384,6 +384,10 @@ int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)
         return -1;
     }
 
+    zmq::clock_t clock;
+    uint64_t now = 0;
+    uint64_t end = 0;
+
     pollfd *pollfds = (pollfd*) malloc (nitems_ * sizeof (pollfd));
     zmq_assert (pollfds);
 
@@ -413,16 +417,21 @@ int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)
 
     bool first_pass = true;
     int nevents = 0;
-    if (timeout_ >= 0)
-        timeout_ /= 1000;
-    else
-        timeout_ = -1;
 
     while (true) {
 
+         //  Compute the timeout for the subsequent poll.
+         int timeout;
+         if (first_pass)
+             timeout = 0;
+         else if (timeout_ < 0)
+             timeout = -1;
+         else
+             timeout = end - now;
+
         //  Wait for events.
         while (true) {
-            int rc = poll (pollfds, nitems_, first_pass ? 0 : timeout_);
+            int rc = poll (pollfds, nitems_, timeout);
             if (rc == -1 && errno == EINTR) {
                 free (pollfds);
                 return -1;
@@ -468,22 +477,33 @@ int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)
                 nevents++;
         }
 
-        //  If there are no events from the first pass (the one with no
+        //  If timout is zero, exit immediately whether there are events or not.
-        //  timeout), do at least the second pass so that we wait.
+        if (timeout_ == 0)
-        if (first_pass && nevents == 0 && timeout_ != 0) {
+            break;
-            first_pass = false;
+
+        //  If there are events to return, we can exit immediately.
+        if (nevents)
+            break;
+
+        //  At this point we are meant to wait for events but there are none.
+        //  If timeout is infinite we can just loop until we get some events.
+        if (timeout_ < 0)
+            continue;
+
+        //  The timeout is finite and there are no events. In the first pass
+        //  we get a timestamp of when the polling have begun. (We assume that
+        //  first pass have taken negligible time). We also compute the time
+        //  when the polling should time out.
+        if (first_pass) {
+            now = clock.now_ms ();
+            end = now + (timeout_ / 1000);
             continue;
         }
 
-        //  If timeout is set to infinite and we have to events to return
+        //  Find out whether timeout have expired.
-        //  we can restart the polling.
+        now = clock.now_ms ();
-        if (timeout_ == -1 && nevents == 0)
+        if (now >= end)
-            continue;
+            break;
-
-        //  TODO: if nevents is zero recompute timeout and loop
-        //  if it is not yet reached.
-
-        break;
     }
 
     free (pollfds);
@@ -491,6 +511,19 @@ int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)
 
 #elif defined ZMQ_POLL_BASED_ON_SELECT
 
+    if (!items_) {
+        errno = EFAULT;
+        return -1;
+    }
+
+    zmq::clock_t clock;
+    uint64_t now = 0;
+    uint64_t end = 0;
+
+    //  Ensure we do not attempt to select () on more than FD_SETSIZE
+    //  file descriptors.
+    zmq_assert (nitems_ <= FD_SETSIZE);
+
     fd_set pollset_in;
     FD_ZERO (&pollset_in);
     fd_set pollset_out;
@@ -500,10 +533,6 @@ int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)
 
     zmq::fd_t maxfd = 0;
 
-    //  Ensure we do not attempt to select () on more than FD_SETSIZE
-    //  file descriptors.
-    zmq_assert (nitems_ <= FD_SETSIZE);
-
     //  Build the fd_sets for passing to select ().
     for (int i = 0; i != nitems_; i++) {
 
@@ -536,11 +565,25 @@ int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)
     }
 
     bool first_pass = true;
-    timeval zero_timeout = {0, 0};
-    timeval timeout = {timeout_ / 1000000, timeout_ % 1000000};
     int nevents = 0;
     fd_set inset, outset, errset;
 
+    //  Compute the timeout for the subsequent poll.
+    timeval timeout;
+    timeval *ptimeout;
+    if (first_pass) {
+        timeout.tv_sec = 0;
+        timeout.tv_usec = 0;
+        ptimeout = &timeout;
+    }
+    else if (timeout_ < 0)
+        ptimeout = NULL;
+    else {
+        timeout.tv_sec = (long) ((end - now) / 1000);
+        timeout.tv_usec = (long) ((end - now) % 1000 * 1000);
+        ptimeout = &timeout;
+    }
+
     while (true) {
 
         //  Wait for events. Ignore interrupts if there's infinite timeout.
@@ -548,8 +591,7 @@ int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)
             memcpy (&inset, &pollset_in, sizeof (fd_set));
             memcpy (&outset, &pollset_out, sizeof (fd_set));
             memcpy (&errset, &pollset_err, sizeof (fd_set));
-            int rc = select (maxfd + 1, &inset, &outset, &errset,
+            int rc = select (maxfd + 1, &inset, &outset, &errset, ptimeout);
-                first_pass ? &zero_timeout : (timeout_ < 0 ? NULL : &timeout));
 #if defined ZMQ_HAVE_WINDOWS
             wsa_assert (rc != SOCKET_ERROR);
 #else
@@ -595,22 +637,33 @@ int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)
                 nevents++;
         }
 
-        //  If there are no events from the first pass (the one with no
+        //  If timout is zero, exit immediately whether there are events or not.
-        //  timout), do at least the second pass so that we wait.
+        if (timeout_ == 0)
-        if (first_pass && nevents == 0 && timeout_ != 0) {
+            break;
-            first_pass = false;
+
+        //  If there are events to return, we can exit immediately.
+        if (nevents)
+            break;
+
+        //  At this point we are meant to wait for events but there are none.
+        //  If timeout is infinite we can just loop until we get some events.
+        if (timeout_ < 0)
+            continue;
+
+        //  The timeout is finite and there are no events. In the first pass
+        //  we get a timestamp of when the polling have begun. (We assume that
+        //  first pass have taken negligible time). We also compute the time
+        //  when the polling should time out.
+        if (first_pass) {
+            now = clock.now_ms ();
+            end = now + (timeout_ / 1000);
             continue;
         }
 
-        //  If timeout is set to infinite and we have to events to return
+        //  Find out whether timeout have expired.
-        //  we can restart the polling.
+        now = clock.now_ms ();
-        if (timeout_ < 0 && nevents == 0)
+        if (now >= end)
-            continue;
+            break;
-
-        //  TODO: if nevents is zero recompute timeout and loop
-        //  if it is not yet reached.
-
-        break;
     }
 
     return nevents;