From 284cdb8ef69455ea47c60eb7533cfe4ddcf090f6 Mon Sep 17 00:00:00 2001
From: Christian Grothoff <christian@grothoff.org>
Date: Fri, 11 Nov 2011 19:56:55 +0000
Subject: fixing 1787

---
 src/fs/Makefile.am            |  2 +-
 src/fs/gnunet-service-fs_pe.c | 36 +++++++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 2 deletions(-)

(limited to 'src')

diff --git a/src/fs/Makefile.am b/src/fs/Makefile.am
index 264bb45d6..8cc0f9bf3 100644
--- a/src/fs/Makefile.am
+++ b/src/fs/Makefile.am
@@ -138,7 +138,7 @@ gnunet_service_fs_LDADD =  \
  $(top_builddir)/src/ats/libgnunetats.la \
  $(top_builddir)/src/core/libgnunetcore.la \
  $(top_builddir)/src/util/libgnunetutil.la \
- $(GN_LIBINTL)
+ $(GN_LIBINTL) -lm
 gnunet_service_fs_DEPENDENCIES = \
   libgnunetfs.la
 
diff --git a/src/fs/gnunet-service-fs_pe.c b/src/fs/gnunet-service-fs_pe.c
index 41dd61a64..200d7a0e4 100644
--- a/src/fs/gnunet-service-fs_pe.c
+++ b/src/fs/gnunet-service-fs_pe.c
@@ -251,6 +251,12 @@ schedule_peer_transmission (void *cls,
 static void
 plan (struct PeerPlan *pp, struct GSF_RequestPlan *rp)
 {
+#define N ((double)128.0)
+  /**
+   * Running average delay we currently impose.
+   */
+  static double avg_delay;
+
   struct GSF_PendingRequestData *prd;
   struct GNUNET_TIME_Relative delay;
 
@@ -259,7 +265,7 @@ plan (struct PeerPlan *pp, struct GSF_RequestPlan *rp)
                          gettext_noop ("# average retransmission delay (ms)"),
                          total_delay * 1000LL / plan_count, GNUNET_NO);
   prd = GSF_pending_request_get_data_ (rp->prl_head->pr);
-  // FIXME: calculate 'rp->priority'!
+  
   if (rp->transmission_counter < 8)
     delay =
         GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS,
@@ -276,6 +282,33 @@ plan (struct PeerPlan *pp, struct GSF_RequestPlan *rp)
   delay.rel_value =
       GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK,
                                 delay.rel_value + 1);
+  /* Add 0.01 to avg_delay to avoid division-by-zero later */
+  avg_delay = (((avg_delay * (N-1.0)) + delay.rel_value) / N) + 0.01;
+
+  /*
+     For the priority, we need to consider a few basic rules:
+     1) if we just started requesting (delay is small), we should
+        virtually always have a priority of zero.
+     2) for requests with average latency, our priority should match
+        the average priority observed on the network
+     3) even the longest-running requests should not be WAY out of
+        the observed average (thus we bound by a factor of 2)
+     4) we add +1 to the observed average priority to avoid everyone
+        staying put at zero (2 * 0 = 0...).
+
+     Using the specific calculation below, we get:
+
+     delay = 0 => priority = 0;
+     delay = avg delay => priority = running-average-observed-priority;
+     delay >> avg_delay => priority = 2 * running-average-observed-priority;
+
+     which satisfies all of the rules above.
+     
+     Note: M_PI_4 = PI/4 = arctan(1)
+  */     
+  rp->priority = round ((GSF_current_priorities + 1.0) * atan (delay.rel_value / avg_delay)) / M_PI_4;
+  /* Note: usage of 'round' and 'atan' requires -lm */
+
   if (rp->transmission_counter != 0)
     delay.rel_value += TTL_DECREMENT;
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
@@ -304,6 +337,7 @@ plan (struct PeerPlan *pp, struct GSF_RequestPlan *rp)
   if (GNUNET_SCHEDULER_NO_TASK != pp->task)
     GNUNET_SCHEDULER_cancel (pp->task);
   pp->task = GNUNET_SCHEDULER_add_now (&schedule_peer_transmission, pp);
+#undef N
 }
 
 
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