- scheduler: compute no_jobs_available correctly

in the presence of multiple scheduling types
    (e.g., locality and job array)
    From Nils Brause

svn path=/trunk/boinc/; revision=19559

checkin_notes

@@ -9145,3 +9145,15 @@ David  12 Nov 2009
     - Mac compile fix
     lib/
         coproc.cpp
+
+David  12 Nov 2009
+    - scheduler: compute no_jobs_available correctly
+        in the presence of multiple scheduling types
+        (e.g., locality and job array)
+        From Nils Brause
+
+    sched/
+        handle_request.cpp
+        sched_array.cpp
+        sched_score.cpp
+        sched_send.cpp

sched/handle_request.cpp

@@ -1113,14 +1113,19 @@ void process_request(char* code_sign_key) {
         }
     }
 
-    // if there's no work, and client isn't returning results,
-    // this isn't an initial RPC,
-    // and client is requesting work, return without accessing DB
+    // If:
+    // - there's no work,
+    // - a config flag is set,
+    // - client isn't returning results,
+    // - this isn't an initial RPC,
+    // - client is requesting work
+    // then return without accessing the DB.
+    // This is an efficiency hack for when servers are overloaded
     //
     if (
-        config.nowork_skip
+        have_no_work
+        && config.nowork_skip
         && requesting_work()
-        && have_no_work
         && (g_request->results.size() == 0)
         && (g_request->hostid != 0)
     ) {
@@ -1132,11 +1137,10 @@ void process_request(char* code_sign_key) {
         }
     }
 
-    // FROM HERE ON DON'T RETURN; goto leave instead
-    // because we've tagged an entry in the work array with our process ID
+    // FROM HERE ON DON'T RETURN; "goto leave" instead
+    // (because ssp->no_work() may have tagged an entry in the work array
+    // with our process ID)
 
-    // now open the database
-    //
     retval = open_database();
     if (retval) {
         send_error_message("Server can't open database", 3600);

sched/sched_array.cpp

@@ -325,7 +325,6 @@ done:
 //
 void send_work_old() {
     if (!work_needed(false)) return;
-    g_wreq->no_jobs_available = true;
     g_wreq->beta_only = false;
     g_wreq->user_apps_only = true;
     g_wreq->infeasible_only = false;

sched/sched_score.cpp

@@ -294,11 +294,12 @@ void send_work_matchmaker() {
         if (jobs.request_satisfied() && slots_scanned>=min_slots) break;
     }
 
-    if (!slots_nonempty) {
+    if (slots_nonempty) {
+        g_wreq->no_jobs_available = false;
+    } else {
         log_messages.printf(MSG_CRITICAL,
             "Job cache is empty - check feeder\n"
         );
-        g_wreq->no_jobs_available = true;
     }
 
     // TODO: trim jobs from tail of list until we pass the EDF check

sched/sched_send.cpp

@@ -1580,6 +1580,11 @@ void send_work() {
         );
     }
 
+    // assume no jobs are available to send;
+    // if this turns out not to be the case, clear this flag
+    //
+    g_wreq->no_jobs_available = true;
+
     if (config.locality_scheduler_fraction > 0) {
         if (drand() < config.locality_scheduler_fraction) {
            if (config.debug_locality)