[PATCH 3/4] agent: avoid tight timer tick when possible

[Daniel Kahn Gillmor]

* agent/gpg-agent.c (need_tick): evaluate whether the short-phase
  handle_tick() is needed.  (handle_connections): on each cycle of the
  select loop, adjust whether we should call handle_tick() or not.
* agent/call-scd.c (start_scd): call interrupt_main_thread_loop() once
  the scdaemon thread context has started up.

--

With this change, an idle gpg-agent that has no scdaemon running only
wakes up once a minute (to check_own_socket).

Signed-off-by: Daniel Kahn Gillmor <dkg at fifthhorseman.net>
---
 agent/call-scd.c  |  4 +++-
 agent/gpg-agent.c | 25 ++++++++++++++++++++++++-
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/agent/call-scd.c b/agent/call-scd.c
index 0f7d570..9ddb978 100644
--- a/agent/call-scd.c
+++ b/agent/call-scd.c
@@ -407,7 +407,9 @@ start_scd (ctrl_t ctrl)
 
   primary_scd_ctx = ctx;
   primary_scd_ctx_reusable = 0;
-
+  /* notify the main loop that something has changed */
+  interrupt_main_thread_loop ();
+  
  leave:
   xfree (abs_homedir);
   if (err)
diff --git a/agent/gpg-agent.c b/agent/gpg-agent.c
index c588e80..827735c 100644
--- a/agent/gpg-agent.c
+++ b/agent/gpg-agent.c
@@ -2241,6 +2241,26 @@ create_directories (void)
 }
 
 
+static int
+need_tick (void)
+{
+#ifdef HAVE_W32_SYSTEM
+  /* We do not know how to interrupt the select loop on Windows, so we
+     always need a short tick there. */
+  return 1;
+#else
+  /* if we were invoked like "gpg-agent cmd arg1 arg2" then we need to
+     watch our parent. */
+  if (parent_pid != (pid_t)(-1))
+    return 1;
+  /* if scdaemon is running, we need to check that it's alive */
+  if (agent_scd_check_running ())
+    return 1;
+  /* otherwise, nothing fine-grained to do. */
+  return 0;
+#endif /*HAVE_W32_SYSTEM*/
+}
+
 
 /* This is the worker for the ticker.  It is called every few seconds
    and may only do fast operations. */
@@ -2299,7 +2319,7 @@ agent_sigusr2_action (void)
 
 #ifndef HAVE_W32_SYSTEM
 /* The signal handler for this program.  It is expected to be run in
-   its own trhead and not in the context of a signal handler.  */
+   its own thread and not in the context of a signal handler.  */
 static void
 handle_signal (int signo)
 {
@@ -2835,6 +2855,9 @@ handle_connections (gnupg_fd_t listen_fd,
          thus a simple assignment is fine to copy the entire set.  */
       read_fdset = fdset;
 
+      /* avoid a fine-grained timer if we don't need one: */
+      timertbl[0].interval.tv_sec = need_tick () ? TIMERTICK_INTERVAL : 0;
+
       /* loop through all timers, fire any registered functions, and
          plan next timer to trigger */
       npth_clock_gettime (&curtime);
-- 
2.10.1