Bug 1539262 - Count the number of prioDatas needed to encode the recorded Origin Telemetry. r=janerik

In order to notify the "prio" ping when we reach the data limit, we need to
keep an accounting of how many prioData elements we'd need to encode what's in
storage.

This also adds the pref reading and topic notification code for the
"origin-telemetry-storage-limit-reached" topic that the "prio" ping observes.

Differential Revision: https://phabricator.services.mozilla.com/D25127

toolkit/components/telemetry/core/TelemetryOrigin.cpp

@@ -8,6 +8,7 @@
 #include "TelemetryOrigin.h"
 
 #include "nsDataHashtable.h"
+#include "nsIObserverService.h"
 #include "nsIXULAppInfo.h"
 #include "TelemetryCommon.h"
 #include "TelemetryOriginEnums.h"
@@ -15,8 +16,11 @@
 #include "mozilla/Atomics.h"
 #include "mozilla/Base64.h"
 #include "mozilla/dom/PrioEncoder.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Services.h"
 #include "mozilla/StaticMutex.h"
 
+#include <cmath>
 #include <type_traits>
 
 using mozilla::ErrorResult;
@@ -79,6 +83,9 @@ class OriginMetricIDHashKey : public PLDHashEntryHdr {
 ////////////////////////////////////////////////////////////////////////
 //
 // PRIVATE STATE, SHARED BY ALL THREADS
+//
+// Access for all of this state (except gInitDone) must be guarded by
+// gTelemetryOriginMutex.
 
 namespace {
 
@@ -112,6 +119,20 @@ typedef nsDataHashtable<OriginMetricIDHashKey, nsTArray<bool>> IdToBoolsMap;
 static nsCString gBatchID;
 #define CANARY_BATCH_ID "decaffcoffee"
 
+// The number of prioData elements needed to encode the contents of storage.
+// Will be some whole multiple of gPrioDatasPerMetric.
+static uint32_t gPrioDataCount = 0;
+
+// Prio has a maximum supported number of bools it can encode at a time.
+// This means a single metric may result in several encoded payloads if the
+// number of origins exceeds the number of bools.
+// Each encoded payload corresponds to an element in the `prioData` array in the
+// "prio" ping.
+// This number is the number of encoded payloads needed per metric, and is
+// equivalent to "how many bitvectors do we need to encode this whole list of
+// origins?"
+static uint32_t gPrioDatasPerMetric;
+
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////
@@ -179,6 +200,9 @@ void TelemetryOrigin::InitializeGlobalState() {
       "fb.com",
   });
 
+  gPrioDatasPerMetric = ceil(static_cast<double>(gOriginsList->Length()) /
+                             PrioEncoder::gNumBooleans);
+
   gOriginToIndexMap = new OriginToIndexMap(gOriginsList->Length());
   for (size_t i = 0; i < gOriginsList->Length(); ++i) {
     gOriginToIndexMap->Put(nsDependentCString((*gOriginsList)[i]), i);
@@ -249,9 +273,32 @@ nsresult TelemetryOrigin::RecordOrigin(OriginMetricID aId,
     return NS_OK;
   }
 
+  if (!gMetricToOriginsMap->Contains(aId)) {
+    // If we haven't recorded anything for this metric yet, we're adding some
+    // prioDatas.
+    gPrioDataCount += gPrioDatasPerMetric;
+  }
+
   auto& originArray = gMetricToOriginsMap->GetOrInsert(aId);
+
+  if (originArray.Contains(aOrigin)) {
+    // If we've already recorded this metric for this origin, then we're going
+    // to need more prioDatas to encode that it happened again.
+    gPrioDataCount += gPrioDatasPerMetric;
+  }
+
   originArray.AppendElement(aOrigin);
 
+  static uint32_t sPrioPingLimit =
+      mozilla::Preferences::GetUint("toolkit.telemetry.prioping.dataLimit", 10);
+  if (gPrioDataCount >= sPrioPingLimit) {
+    nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
+    if (os) {
+      os->NotifyObservers(nullptr, "origin-telemetry-storage-limit-reached",
+                          nullptr);
+    }
+  }
+
   return NS_OK;
 }
 
@@ -277,6 +324,7 @@ nsresult TelemetryOrigin::GetOriginSnapshot(bool aClear, JSContext* aCx,
       // squeeze for not enough juice.
 
       gMetricToOriginsMap->SwapElements(copy);
+      gPrioDataCount = 0;
     } else {
       auto iter = gMetricToOriginsMap->ConstIter();
       for (; !iter.Done(); iter.Next()) {
@@ -410,6 +458,7 @@ nsresult TelemetryOrigin::GetEncodedOriginSnapshot(
   if (aClear) {
     StaticMutexAutoLock lock(gTelemetryOriginMutex);
     gMetricToOriginsMap->Clear();
+    gPrioDataCount = 0;
   }
 
   aSnapshot.setObject(*prioDataArray);