Add assertion of the invariant for the spark counters

The invariant is: created = converted + remaining + gcd + fizzled
Since sparks move between capabilities, we have to aggregate the
counters over all capabilities. This in turn means we can only check
the invariant at stable points where all but one capabilities are
stopped. We can do this at shutdown time and before and after a global
synchronised GC.

1 files changed, 35 insertions, 0 deletions

diff --git a/rts/Capability.c b/rts/Capability.c
index d93c9c1eda..410d3d0a9c 100644
--- a/rts/Capability.c
+++ b/rts/Capability.c
@@ -843,6 +843,10 @@ shutdownCapabilities(Task *task, rtsBool safe)
         shutdownCapability(&capabilities[i], task, safe);
     }
     traceCapsetDelete(CAPSET_OSPROCESS_DEFAULT);
+
+#if defined(THREADED_RTS)
+    ASSERT(checkSparkCountInvariant());
+#endif
 }
 
 static void
@@ -913,3 +917,34 @@ markCapabilities (evac_fn evac, void *user)
         markCapability(evac, user, &capabilities[n], rtsFalse);
     }
 }
+
+#if defined(THREADED_RTS)
+rtsBool checkSparkCountInvariant (void)
+{
+    SparkCounters sparks = { 0, 0, 0, 0, 0, 0 };
+    StgWord64 remaining = 0;
+    nat i;
+
+    for (i = 0; i < n_capabilities; i++) {
+        sparks.created   += capabilities[i].spark_stats.created;
+        sparks.dud       += capabilities[i].spark_stats.dud;
+        sparks.overflowed+= capabilities[i].spark_stats.overflowed;
+        sparks.converted += capabilities[i].spark_stats.converted;
+        sparks.gcd       += capabilities[i].spark_stats.gcd;
+        sparks.fizzled   += capabilities[i].spark_stats.fizzled;
+        remaining        += sparkPoolSize(capabilities[i].sparks);
+    }
+    
+    /* The invariant is
+     *   created = converted + remaining + gcd + fizzled
+     */
+    debugTrace(DEBUG_sparks,"spark invariant: %ld == %ld + %ld + %ld + %ld "
+                            "(created == converted + remaining + gcd + fizzled)",
+                            sparks.created, sparks.converted, remaining,
+                            sparks.gcd, sparks.fizzled);
+
+    return (sparks.created ==
+              sparks.converted + remaining + sparks.gcd + sparks.fizzled);
+
+}
+#endif