agent: Create framework of scheduled timers.

agent/gpg-agent.c (handle_tick): Remove intermittent call to
check_own_socket.
(tv_is_set): Add inline helper function for readability.
(handle_connections) Create general table of pending scheduled
timeouts.

--

handle_tick() does fine-grained, rapid activity.  check_own_socket()
is supposed to happen at a different interval.

Mixing the two of them makes it a requirement that one interval be a
multiple of the other, which isn't ideal if there are different delay
strategies that we might want in the future.

Creating an extensible regular timer framework in handle_connections
should make it possible to have any number of cadenced timers fire
regularly, without requiring that they happen in cadences related to
each other.

It should also make it possible to dynamically change the cadence of
any regularly-scheduled timeout.

Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>

Gbp-Pq: Topic gpg-agent-idling
Gbp-Pq: Name agent-Create-framework-of-scheduled-timers.patch

agent/gpg-agent.c

@@ -2379,12 +2379,8 @@ create_directories (void)
 static void
 handle_tick (void)
 {
-  static time_t last_minute;
   struct stat statbuf;
 
-  if (!last_minute)
-    last_minute = time (NULL);
-
   /* Check whether the scdaemon has died and cleanup in this case. */
   agent_scd_check_aliveness ();
 
@@ -2404,15 +2400,6 @@ handle_tick (void)
     }
 #endif /*HAVE_W32_SYSTEM*/
 
-  /* Code to be run from time to time.  */
-#if CHECK_OWN_SOCKET_INTERVAL > 0
-  if (last_minute + CHECK_OWN_SOCKET_INTERVAL <= time (NULL))
-    {
-      check_own_socket ();
-      last_minute = time (NULL);
-    }
-#endif
-
   /* Need to check for expired cache entries.  */
   agent_cache_housekeeping ();
 
@@ -2823,6 +2810,15 @@ start_connection_thread_ssh (void *arg)
 }
 
 
+/* helper function for readability: test whether a given struct
+   timespec is set to all-zeros */
+static inline int
+tv_is_set (struct timespec tv)
+{
+  return tv.tv_sec || tv.tv_nsec;
+}
+
+
 /* Connection handler loop.  Wait for connection requests and spawn a
    thread after accepting a connection.  */
 static void
@@ -2840,9 +2836,11 @@ handle_connections (gnupg_fd_t listen_fd,
   gnupg_fd_t fd;
   int nfd;
   int saved_errno;
+  int idx;
   struct timespec abstime;
   struct timespec curtime;
   struct timespec timeout;
+  struct timespec *select_timeout;
 #ifdef HAVE_W32_SYSTEM
   HANDLE events[2];
   unsigned int events_set;
@@ -2859,6 +2857,14 @@ handle_connections (gnupg_fd_t listen_fd,
     { "browser", start_connection_thread_browser },
     { "ssh",    start_connection_thread_ssh   }
   };
+  struct {
+    struct timespec interval;
+    void (*func) (void);
+    struct timespec next;
+  } timertbl[] = {
+    { { TIMERTICK_INTERVAL, 0 }, handle_tick },
+    { { CHECK_OWN_SOCKET_INTERVAL, 0 }, check_own_socket }
+  };
 
 
   ret = npth_attr_init(&tattr);
@@ -2966,9 +2972,6 @@ handle_connections (gnupg_fd_t listen_fd,
   listentbl[2].l_fd = listen_fd_browser;
   listentbl[3].l_fd = listen_fd_ssh;
 
-  npth_clock_gettime (&abstime);
-  abstime.tv_sec += TIMERTICK_INTERVAL;
-
   for (;;)
     {
       /* Shutdown test.  */
@@ -3003,18 +3006,46 @@ handle_connections (gnupg_fd_t listen_fd,
          thus a simple assignment is fine to copy the entire set.  */
       read_fdset = fdset;
 
+      /* loop through all timers, fire any registered functions, and
+         plan next timer to trigger */
       npth_clock_gettime (&curtime);
-      if (!(npth_timercmp (&curtime, &abstime, <)))
-	{
-	  /* Timeout.  */
-	  handle_tick ();
-	  npth_clock_gettime (&abstime);
-	  abstime.tv_sec += TIMERTICK_INTERVAL;
-	}
-      npth_timersub (&abstime, &curtime, &timeout);
+      abstime.tv_sec = abstime.tv_nsec = 0;
+      for (idx=0; idx < DIM(timertbl); idx++)
+        {
+          /* schedule any unscheduled timers */
+          if ((!tv_is_set (timertbl[idx].next)) && tv_is_set (timertbl[idx].interval))
+            npth_timeradd (&timertbl[idx].interval, &curtime, &timertbl[idx].next);
+          /* if a timer is due, fire it ... */
+          if (tv_is_set (timertbl[idx].next))
+            {
+              if (!(npth_timercmp (&curtime, &timertbl[idx].next, <)))
+                {
+                  timertbl[idx].func ();
+                  npth_clock_gettime (&curtime);
+                  /* ...and reschedule it, if desired: */
+                  if (tv_is_set (timertbl[idx].interval))
+                    npth_timeradd (&timertbl[idx].interval, &curtime, &timertbl[idx].next);
+                  else
+                    timertbl[idx].next.tv_sec = timertbl[idx].next.tv_nsec = 0;
+                }
+            }
+          /* accumulate next timer to come due in abstime: */
+          if (tv_is_set (timertbl[idx].next) &&
+              ((!tv_is_set (abstime)) ||
+               (npth_timercmp (&abstime, &timertbl[idx].next, >))))
+            abstime = timertbl[idx].next;
+        }
+      /* choose a timeout for the select loop: */
+      if (tv_is_set (abstime))
+        {
+          npth_timersub (&abstime, &curtime, &timeout);
+          select_timeout = &timeout;
+        }
+      else
+          select_timeout = NULL;
 
 #ifndef HAVE_W32_SYSTEM
-      ret = npth_pselect (nfd+1, &read_fdset, NULL, NULL, &timeout,
+      ret = npth_pselect (nfd+1, &read_fdset, NULL, NULL, select_timeout,
                           npth_sigev_sigmask ());
       saved_errno = errno;
 
@@ -3024,7 +3055,7 @@ handle_connections (gnupg_fd_t listen_fd,
           handle_signal (signo);
       }
 #else
-      ret = npth_eselect (nfd+1, &read_fdset, NULL, NULL, &timeout,
+      ret = npth_eselect (nfd+1, &read_fdset, NULL, NULL, select_timeout,
                           events, &events_set);
       saved_errno = errno;
 
@@ -3069,7 +3100,6 @@ handle_connections (gnupg_fd_t listen_fd,
 
       if (!shutdown_pending)
         {
-          int idx;
           ctrl_t ctrl;
           npth_t thread;