Bug 1514392 - Use fallback process start time, even if inconsistent r=wlach,chutten

Differential Revision: https://phabricator.services.mozilla.com/D19645

--HG--
extra : moz-landing-system : lando

toolkit/components/telemetry/Scalars.yaml

@@ -1806,6 +1806,20 @@ telemetry:
     record_in_processes:
       - 'main'
 
+  process_creation_timestamp_inconsistent:
+    bug_numbers:
+      - 1514392
+    description: >
+      The number of times ProcessCreation saw an inconsistent value.
+    expires: "72"
+    kind: uint
+    notification_emails:
+      - jrediger@mozilla.com
+    release_channel_collection: opt-out
+    record_in_processes:
+      - 'main'
+      - 'content'
+
 telemetry.discarded:
   accumulations:
     bug_numbers:

toolkit/components/telemetry/app/TelemetryUtils.jsm

@@ -217,11 +217,7 @@ var TelemetryUtils = {
    * or (non-monotonic) Date value if this fails back.
    */
   monotonicNow() {
-    try {
-      return Services.telemetry.msSinceProcessStart();
-    } catch (ex) {
-      return Date.now();
-    }
+    return Services.telemetry.msSinceProcessStart();
   },
 
   /**

toolkit/components/telemetry/core/TelemetryCommon.cpp

@@ -14,6 +14,7 @@
 #include "nsThreadUtils.h"
 #include "nsVersionComparator.h"
 #include "TelemetryProcessData.h"
+#include "Telemetry.h"
 
 namespace mozilla {
 namespace Telemetry {
@@ -83,11 +84,15 @@ bool CanRecordProduct(SupportedProduct aProducts) {
 }
 
 nsresult MsSinceProcessStart(double* aResult) {
-  bool error;
-  *aResult = (TimeStamp::NowLoRes() - TimeStamp::ProcessCreation(&error))
-                 .ToMilliseconds();
-  if (error) {
-    return NS_ERROR_NOT_AVAILABLE;
+  bool isInconsistent = false;
+  *aResult =
+      (TimeStamp::NowLoRes() - TimeStamp::ProcessCreation(&isInconsistent))
+          .ToMilliseconds();
+
+  if (isInconsistent) {
+    Telemetry::ScalarAdd(
+        Telemetry::ScalarID::TELEMETRY_PROCESS_CREATION_TIMESTAMP_INCONSISTENT,
+        1);
   }
   return NS_OK;
 }

toolkit/components/telemetry/docs/data/main-ping.rst

@@ -86,8 +86,6 @@ The length of the current session so far in seconds.
 This uses a monotonic clock, so this may mismatch with other measurements that
 are not monotonic like calculations based on ``Date.now()``.
 
-If the monotonic clock failed, this will be ``-1``.
-
 Note that this currently does not behave consistently over our supported platforms:
 
 * On Windows this uses ``GetTickCount64()``, which does increase over sleep periods
@@ -101,8 +99,6 @@ subsessionLength
 The length of this subsession in seconds.
 This uses a monotonic clock, so this may mismatch with other measurements that are not monotonic (e.g. based on ``Date.now()``).
 
-If ``sessionLength`` is ``-1``, the monotonic clock is not working.
-
 Also see the remarks for ``sessionLength`` on platform consistency.
 
 processes

toolkit/components/telemetry/pings/TelemetrySession.jsm

@@ -88,21 +88,12 @@ function generateUUID() {
   return str.substring(1, str.length - 1);
 }
 
-function getMsSinceProcessStart() {
-  try {
-    return Telemetry.msSinceProcessStart();
-  } catch (ex) {
-    // If this fails return a special value.
-    return -1;
-  }
-}
-
 /**
  * This is a policy object used to override behavior for testing.
  */
 var Policy = {
   now: () => new Date(),
-  monotonicNow: getMsSinceProcessStart,
+  monotonicNow: Utils.monotonicNow,
   generateSessionUUID: () => generateUUID(),
   generateSubsessionUUID: () => generateUUID(),
   setSchedulerTickTimeout: (callback, delayMs) => setTimeout(callback, delayMs),