Bug 748914 - Part 2: add a clear() method to JS histograms; r=taras

toolkit/components/telemetry/Telemetry.cpp

@@ -461,6 +461,19 @@ JSHistogram_Snapshot(JSContext *cx, unsigned argc, jsval *vp)
   }
 }
 
+JSBool
+JSHistogram_Clear(JSContext *cx, unsigned argc, jsval *vp)
+{
+  JSObject *obj = JS_THIS_OBJECT(cx, vp);
+  if (!obj) {
+    return JS_FALSE;
+  }
+
+  Histogram *h = static_cast<Histogram*>(JS_GetPrivate(obj));
+  h->Clear();
+  return JS_TRUE;
+}
+
 nsresult 
 WrapAndReturnHistogram(Histogram *h, JSContext *cx, jsval *ret)
 {
@@ -475,8 +488,9 @@ WrapAndReturnHistogram(Histogram *h, JSContext *cx, jsval *ret)
   if (!obj)
     return NS_ERROR_FAILURE;
   JS::AutoObjectRooter root(cx, obj);
-  if (!(JS_DefineFunction (cx, obj, "add", JSHistogram_Add, 1, 0)
-        && JS_DefineFunction (cx, obj, "snapshot", JSHistogram_Snapshot, 1, 0))) {
+  if (!(JS_DefineFunction(cx, obj, "add", JSHistogram_Add, 1, 0)
+        && JS_DefineFunction(cx, obj, "snapshot", JSHistogram_Snapshot, 0, 0)
+        && JS_DefineFunction(cx, obj, "clear", JSHistogram_Clear, 0, 0))) {
     return NS_ERROR_FAILURE;
   }
   *ret = OBJECT_TO_JSVAL(obj);

toolkit/components/telemetry/nsITelemetry.idl

@@ -158,6 +158,7 @@ interface nsITelemetry : nsISupports
    * The returned object has the following functions:
    *   add(int) - Adds an int value to the appropriate bucket
    *   snapshot() - Returns a snapshot of the histogram with the same data fields as in histogramSnapshots()
+   *   clear() - Zeros out the histogram's buckets and sum
    */
   [implicit_jscontext]
   jsval newHistogram(in ACString name, in PRUint32 min, in PRUint32 max, in PRUint32 bucket_count, in unsigned long histogram_type);

toolkit/components/telemetry/tests/unit/test_nsITelemetry.js

@@ -39,6 +39,20 @@ function test_histogram(histogram_type, name, min, max, bucket_count) {
   var s = h.snapshot().counts;
   do_check_eq(s[0], 2)
   do_check_eq(s[1], 2)
+
+  // Check that clearing works.
+  h.clear();
+  var s = h.snapshot();
+  for each(var i in s.counts) {
+    do_check_eq(i, 0);
+  }
+  do_check_eq(s.sum, 0);
+
+  h.add(0);
+  h.add(1);
+  var c = h.snapshot().counts;
+  do_check_eq(c[0], 1);
+  do_check_eq(c[1], 1);
 }
 
 function expect_fail(f) {