Fix bug with reporting negative allocation rate

Author: alexander-yakushev

build.boot

@@ -1,6 +1,6 @@
 (task-options!
  pom {:project     'com.clojure-goes-fast/jvm-alloc-rate-meter
-      :version     "0.1.3"
+      :version     "0.1.4-SNAPSHOT"
       :description "Measure JVM heap allocation rate in real time"
       :url         "http://github.com/clojure-goes-fast/jvm-alloc-rate-meter"
       :scm         {:url "http://github.com/clojure-goes-fast/jvm-alloc-rate-meter"}

src/jvm_alloc_rate_meter/MeterThread.java

@@ -39,22 +39,24 @@ public void run() {
         BigInteger lastThreadAllocated = BigInteger.valueOf(-1);
         try {
             while (doRun) {
-                long heapUsage = usedHeap();
-                long gcCounts = gcCounts();
-                BigInteger threadAllocated = allocatedByAllThreads();
                 long time = System.currentTimeMillis();
-
                 double multiplier = 1000.0 / (time - lastTime);
+
+                long heapUsage = usedHeap();
+                long gcCounts = gcCounts();
                 long deltaUsage = heapUsage - lastHeapUsage;
 
+                BigInteger threadAllocated = allocatedByAllThreads();
+                BigInteger deltaAllocated = threadAllocated.subtract(lastThreadAllocated);
+
                 if (lastTime != 0) {
                     if ((gcCounts == lastGcCounts) && (deltaUsage >= 0)) {
                         long rate = Math.round(deltaUsage * multiplier);
                         callback.accept(rate);
                     } else if (threadAllocated.compareTo(BigInteger.ZERO) >= 0 &&
                                lastThreadAllocated.compareTo(BigInteger.ZERO) >= 0 &&
-                               threadAllocated.compareTo(BigInteger.ZERO) >= 0) {
-                        long rate = Math.round(threadAllocated.subtract(lastThreadAllocated).longValue() * multiplier);
+                               deltaAllocated.compareTo(BigInteger.ZERO) >= 0) {
+                        long rate = Math.round(deltaAllocated.longValue() * multiplier);
                         callback.accept(rate);
                     } else {
                         // Apparently, neither approach did well, just skip this