From 3fda3d9864d6f365eb2b0fb87ecc5ea098d3bfdc Mon Sep 17 00:00:00 2001
From: koennecke <mark.koennecke@psi.ch>
Date: Thu, 24 Nov 2016 13:49:07 +0100
Subject: [PATCH] Added exponential backoff when errors occur in sicspoll

---
 polldriv.c |  2 --
 polldriv.h |  1 +
 sicspoll.c | 38 ++++++++++++++++++++++++++++++++++++--
 3 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/polldriv.c b/polldriv.c
index de89f650..ce27b387 100644
--- a/polldriv.c
+++ b/polldriv.c
@@ -36,7 +36,6 @@ static int pollHdb(struct __POLLDRIV *self, SConnection * pCon)
 
   assert(node != NULL);
 
-  self->nextPoll = time(NULL) + self->pollIntervall;
   if (GetHipadabaPar(node, &newVal, pCon) == 1) {
 	ReleaseHdbValue(&newVal);
     return 1;
@@ -84,7 +83,6 @@ static int pollScript(struct __POLLDRIV *self, SConnection * pCon)
   int status;
   Tcl_Interp *pTcl = InterpGetTcl(pServ->pSics);
 
-  self->nextPoll = time(NULL) + self->pollIntervall;
 
   MacroPush(pCon);
   status = Tcl_Eval(pTcl, (char *) self->objPointer);
diff --git a/polldriv.h b/polldriv.h
index 3100dba0..5ca12ca1 100644
--- a/polldriv.h
+++ b/polldriv.h
@@ -16,6 +16,7 @@ typedef struct __POLLDRIV {
   void *objPointer;             /* a pointer to the object */
   time_t nextPoll;              /* next polling time */
   int pollIntervall;            /* poll intervall */
+  int actualPollIntervall;      /* for supporting exponential backoff */
   int (*isDue) (struct __POLLDRIV * self, time_t now, SConnection * pCon);
   /* function called to determine if this object must be polled */
   int (*poll) (struct __POLLDRIV * self, SConnection * pCon);
diff --git a/sicspoll.c b/sicspoll.c
index 33be09ff..c26f93af 100644
--- a/sicspoll.c
+++ b/sicspoll.c
@@ -9,6 +9,11 @@
  * Copyright: see COPYRIGHT
  * 
  * Mark Koennecke, November-December 2006
+ *
+ * Implemented exponential backoff up to 6 minutes when polling fails. This in order to 
+ * reduce the number of error messages in the logs if something is MIA
+ *
+ * Mark Koennecke, November 2016
  */
 
 #include <stdlib.h>
@@ -109,7 +114,33 @@ void SicsPollSignal(void *pData, int iSignal, void *pSigData)
     }
   }
 }
-
+/*----------------------------------------------------------------------
+This function implements the exponential backoff when there is a failure
+in polling
+------------------------------------------------------------------------*/
+static void advancePoll(pPollDriv poll, int status)
+{
+  if(status == 1) {
+    /* success */
+    poll->actualPollIntervall = poll->pollIntervall;
+  } else {
+    /*
+      poll error, backoff
+    */
+    if(poll->actualPollIntervall < poll->pollIntervall){
+      poll->actualPollIntervall = 2 * poll->pollIntervall;
+    } else {
+      poll->actualPollIntervall = 2 * poll->actualPollIntervall;
+      /*
+	poll at least every 6 minutes
+      */
+      if(poll->actualPollIntervall > 360){
+	poll->actualPollIntervall = 360;
+      }
+    }
+  }
+  poll->nextPoll = time(NULL) + poll->actualPollIntervall;
+}
 /*----------------------------------------------------------------------*/
 static int PollTask(void *data)
 {
@@ -141,7 +172,8 @@ static int PollTask(void *data)
     poll = (pPollDriv) LLDnodePtr(self->pollList);
     if (status != 0 && poll != NULL) {
       if (poll->isDue(poll, now, self->pCon)) {
-        poll->poll(poll, self->pCon);
+        status = poll->poll(poll, self->pCon);
+	advancePoll(poll,status);
       }
     }
   }
@@ -312,6 +344,7 @@ int SICSPollWrapper(SConnection * pCon, SicsInterp * pSics, void *pData,
         return 0;
       }
       driv->pollIntervall = iVal;
+      driv->actualPollIntervall = iVal;
       SCSendOK(pCon);
       return 1;
     } else {
@@ -346,6 +379,7 @@ int SICSPollWrapper(SConnection * pCon, SicsInterp * pSics, void *pData,
       return 0;
     }
     status = driv->poll(driv, pCon);
+    advancePoll(driv,status);
     if (status != 1) {
       SCWrite(pCon, "ERROR: polling object", eError);
       return 0;