bug 1440673 - Summarize events to a keyed scalar r=Dexter

Telemetry Events will now be counted in the keyed scalar
"telemetry.event_counts" even if their category is not enabled for recording.

The keys will be category#method#object and a follow-up commit will expand the
process limit of the number of these from 100 to 500, configurable by pref.

Unfortunately Event Telemetry needs a special API so that an event recorded in
multiple processes will be summarized to those processes separately.

MozReview-Commit-ID: 7dKcM3SXO6r

--HG--
extra : rebase_source : 42af54472ac648165ac64bc5ab5a5a666830efe8

toolkit/components/telemetry/Scalars.yaml

@@ -1033,6 +1033,23 @@ telemetry:
     record_in_processes:
       - 'main'
 
+  event_counts:
+    bug_numbers:
+      - 1440673
+    description: >
+      The counts of events recorded in the process, category, method, and
+      object of the key, even if event recording for the category was not
+      enabled.
+    expires: never
+    kind: uint
+    keyed: true
+    notification_emails:
+      - telemetry-client-dev@mozilla.com
+      - chutten@mozilla.com
+    release_channel_collection: opt-out
+    record_in_processes:
+      - 'all'
+
 telemetry.discarded:
   accumulations:
     bug_numbers:

toolkit/components/telemetry/TelemetryEvent.cpp

@@ -25,6 +25,7 @@
 #include "TelemetryCommon.h"
 #include "TelemetryEvent.h"
 #include "TelemetryEventData.h"
+#include "TelemetryScalar.h"
 #include "ipc/TelemetryIPCAccumulator.h"
 
 using mozilla::StaticMutex;
@@ -380,7 +381,7 @@ CanRecordEvent(const StaticMutexAutoLock& lock, const EventKey& eventKey,
     }
   }
 
-  return gEnabledCategories.GetEntry(GetCategory(lock, eventKey));
+  return true;
 }
 
 bool
@@ -469,14 +470,24 @@ RecordEvent(const StaticMutexAutoLock& lock, ProcessID processType,
     return RecordEventResult::ExpiredEvent;
   }
 
+  // Check whether the extra keys passed are valid.
+  if (!CheckExtraKeysValid(*eventKey, extra)) {
+    return RecordEventResult::InvalidExtraKey;
+  }
+
   // Check whether we can record this event.
   if (!CanRecordEvent(lock, *eventKey, processType)) {
     return RecordEventResult::Ok;
   }
 
-  // Check whether the extra keys passed are valid.
-  if (!CheckExtraKeysValid(*eventKey, extra)) {
-    return RecordEventResult::InvalidExtraKey;
+  // Count the number of times this event has been recorded, even if its
+  // category does not have recording enabled.
+  TelemetryScalar::SummarizeEvent(UniqueEventName(category, method, object),
+                                  processType, eventKey->dynamic);
+
+  // Check whether this event's category has recording enabled
+  if (!gEnabledCategories.GetEntry(GetCategory(lock, *eventKey))) {
+    return RecordEventResult::Ok;
   }
 
   // Add event record.

toolkit/components/telemetry/TelemetryScalar.cpp

@@ -2513,6 +2513,39 @@ TelemetryScalar::RegisterScalars(const nsACString& aCategoryName,
   return NS_OK;
 }
 
+/**
+ * Count in Scalars how many of which events were recorded. See bug 1440673
+ *
+ * Event Telemetry unfortunately cannot use vanilla ScalarAdd because it needs
+ * to summarize events recorded in different processes to the
+ * telemetry.event_counts of the same process. Including "dynamic".
+ *
+ * @param aUniqueEventName - expected to be category#object#method
+ * @param aProcessType - the process of the event being summarized
+ * @param aDynamic - whether the event being summarized was dynamic
+ */
+void
+TelemetryScalar::SummarizeEvent(const nsCString& aUniqueEventName,
+                                ProcessID aProcessType, bool aDynamic)
+{
+  MOZ_ASSERT(XRE_IsParentProcess(), "Only summarize events in the parent process");
+  if (!XRE_IsParentProcess()) {
+    return;
+  }
+
+  StaticMutexAutoLock lock(gTelemetryScalarsMutex);
+  ScalarKey scalarKey{static_cast<uint32_t>(ScalarID::TELEMETRY_EVENT_COUNTS), aDynamic};
+  KeyedScalar* scalar = nullptr;
+  nsresult rv = internal_GetKeyedScalarByEnum(lock, scalarKey, aProcessType, &scalar);
+
+  if (NS_FAILED(rv)) {
+    NS_WARNING("NS_FAILED getting keyed scalar telemetry.event_counts. Wut.");
+    return;
+  }
+
+  scalar->AddValue(NS_ConvertASCIItoUTF16(aUniqueEventName), 1);
+}
+
 /**
  * Resets all the stored scalars. This is intended to be only used in tests.
  */

toolkit/components/telemetry/TelemetryScalar.h

@@ -66,6 +66,10 @@ void SetMaximum(mozilla::Telemetry::ScalarID aId, const nsAString& aKey, uint32_
 nsresult RegisterScalars(const nsACString& aCategoryName, JS::Handle<JS::Value> aScalarData,
                          bool aBuiltin, JSContext* cx);
 
+// Event Summary
+void SummarizeEvent(const nsCString& aUniqueEventName,
+                    mozilla::Telemetry::ProcessID aProcessType, bool aDynamic);
+
 // Only to be used for testing.
 void ClearScalars();