diff --git a/checkin_notes b/checkin_notes
index 448c9b79de..c1299baec4 100755
--- a/checkin_notes
+++ b/checkin_notes
@@ -6206,3 +6206,12 @@ Karl 2003/09/05
 
     Sched/
         handle_request.C
+
+David  Sept 6 2003
+    - fixed bug where do_select wasn't sleeping
+        when there are no fds (doh!!)
+
+    client/
+        net_xfer.C,h
+    lib/
+        util.C
diff --git a/client/net_xfer.C b/client/net_xfer.C
index 00e95151c5..3351d249a0 100644
--- a/client/net_xfer.C
+++ b/client/net_xfer.C
@@ -296,13 +296,11 @@ int NET_XFER_SET::remove(NET_XFER* nxp) {
 bool NET_XFER_SET::poll() {
     double bytes_xferred;
     int retval;
-    struct timeval timeout;
     time_t t = time(0);
     bool action = false;
 
     while (1) {
-        timeout.tv_sec = timeout.tv_usec = 0;
-        retval = do_select(bytes_xferred, timeout);
+        retval = do_select(bytes_xferred, 0);
         if (retval) break;
         if (bytes_xferred == 0) break;
         action = true;
@@ -311,6 +309,11 @@ bool NET_XFER_SET::poll() {
     return action;
 }
 
+static void double_to_timeval(double x, timeval& t) {
+    t.tv_sec = (int)x;
+    t.tv_usec = (int)(1000000*(x - (int)x));
+}
+
 // Wait at most x seconds for network I/O to become possible,
 // then do up to about .5 seconds of I/O.
 // This is used only by the cmdline client, to sleep without slowing down I/O.
@@ -318,11 +321,8 @@ bool NET_XFER_SET::poll() {
 int NET_XFER_SET::net_sleep(double x) {
     int retval;
     double bytes_xferred;
-    struct timeval timeout;
 
-    timeout.tv_sec = (int)x;
-    timeout.tv_usec = (int)(1000000*(x - (int)x));
-    retval = do_select(bytes_xferred, timeout);
+    retval = do_select(bytes_xferred, x);
     if (retval) return retval;
     if (bytes_xferred) {
         return poll();
@@ -334,10 +334,11 @@ int NET_XFER_SET::net_sleep(double x) {
 // then do I/O on as many sockets as possible, subject to rate limits
 // Transfer at most one block per socket.
 //
-int NET_XFER_SET::do_select(double& bytes_transferred, timeval& timeout) {
+int NET_XFER_SET::do_select(double& bytes_transferred, double timeout) {
     int n, fd, retval, nsocks_queried;
     socklen_t i;
     NET_XFER *nxp;
+    struct timeval tv;
 
     ScopeMessages scope_messages(log_messages, ClientMessages::DEBUG_NET_XFER);
 
@@ -387,8 +388,13 @@ int NET_XFER_SET::do_select(double& bytes_transferred, timeval& timeout) {
         }
         FD_SET(nxp->socket, &error_fds);
     }
-    if (nsocks_queried==0) return 0;
-    n = select(FD_SETSIZE, &read_fds, &write_fds, &error_fds, &timeout);
+    if (nsocks_queried==0) {
+        boinc_sleep(timeout);
+        return 0;
+    }
+
+    double_to_timeval(timeout, tv);
+    n = select(FD_SETSIZE, &read_fds, &write_fds, &error_fds, &tv);
     scope_messages.printf(
         "NET_XFER_SET::do_select(): queried %d, returned %d\n",
         nsocks_queried, n
diff --git a/client/net_xfer.h b/client/net_xfer.h
index bea57314bb..bb80ecfe80 100644
--- a/client/net_xfer.h
+++ b/client/net_xfer.h
@@ -89,7 +89,7 @@ public:
     int remove(NET_XFER*);
     bool poll();
     int net_sleep(double);
-    int do_select(double& bytes_transferred, struct timeval& timeout);
+    int do_select(double& bytes_transferred, double timeout);
     NET_XFER* lookup_fd(int);   // lookup by fd
     void check_active(bool&, bool&);
 };
diff --git a/doc/api.php b/doc/api.php
index 642645b950..f12a8fb9a1 100644
--- a/doc/api.php
+++ b/doc/api.php
@@ -35,7 +35,6 @@ For example, instead of
 </pre>
 </p>
 the application might use
-<p>
 <pre>
     char resolved_name[256];
     retval = boinc_resolve_filename(\"my_file\", resolved_name);
@@ -70,8 +69,16 @@ then call
 <pre>
     void boinc_checkpoint_completed();
 </pre>
-A call to <tt>boinc_time_to_checkpoint()</tt> is extremely fast,
-so there is little penalty in calling it frequently.
+<tt>boinc_time_to_checkpoint()</tt> is fast
+(it usually makes no system calls),
+so can be called frequently (hundreds or thousands of times a second).
+
+<p>
+<tt>boinc_time_to_checkpoint()</tt> performs other time-based functions;
+e.g. it periodically measures the application's CPU time and
+reports it to the core client.
+So, even for applications that don't do checkpointing,
+it should be called at least once a second.
 
 <h3>Atomic file update</h3>
 <p>
@@ -111,14 +118,13 @@ This is done using
 <h3>Communicating with the core client</h3>
 <p>
 The core client GUI displays the percent done of workunits in progress.
-To keep this display current, an application should
-periodically call
+To keep this display current, an application should periodically call
 <pre>
    boinc_fraction_done(double fraction_done);
 </pre>
 The <tt>fraction_done</tt> argument is a rough estimate of the
 workunit fraction complete (0 to 1).
-This function is extremely fast and can be called often.
+This function is fast and can be called frequently.
 
 <p>
 The following functions get information from the core client;
@@ -150,7 +156,7 @@ list_item("team_expavg_credit", " team's recent average work per day.");
 list_end();
 echo "
 <p>
-It may call
+An application may call
 <pre>
     int boinc_cpu_time(double &cpu_time, double& working_set_size);
 </pre>
diff --git a/lib/util.C b/lib/util.C
index 9889e6c437..fcfd576697 100755
--- a/lib/util.C
+++ b/lib/util.C
@@ -175,7 +175,8 @@ void boinc_sleep(double seconds) {
     ::Sleep((int)(1000*seconds));
 #else
     sleep((int)seconds);
-    usleep((int)fmod(seconds*1000000,1000000));
+    int x = (int)fmod(seconds*1000000,1000000);
+    if (x) usleep(x);
 #endif
 }