Bug 1542833 - Collect cold startup scalar r=chutten,florian

Differential Revision: https://phabricator.services.mozilla.com/D27953

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

browser/components/BrowserGlue.jsm

@@ -1254,6 +1254,24 @@ BrowserGlue.prototype = {
     } catch (ex) {}
   },
 
+  _collectStartupConditionsTelemetry() {
+    let nowSeconds = Math.round(Date.now() / 1000);
+    // Don't include cases where we don't have the pref. This rules out the first install
+    // as well as the first run of a build since this was introduced. These could by some
+    // definitions be referred to as "cold" startups, but probably not since we likely
+    // just wrote many of the files we use to disk. This way we should approximate a lower
+    // bound to the number of cold startups rather than an upper bound.
+    let lastCheckSeconds = Services.prefs.getIntPref("browser.startup.lastColdStartupCheck", nowSeconds);
+    Services.prefs.setIntPref("browser.startup.lastColdStartupCheck", nowSeconds);
+    try {
+      let secondsSinceLastOSRestart = Services.startup.secondsSinceLastOSRestart;
+      let isColdStartup = nowSeconds - secondsSinceLastOSRestart > lastCheckSeconds;
+      Services.telemetry.scalarSet("startup.is_cold", isColdStartup);
+    } catch (ex) {
+      Cu.reportError(ex);
+    }
+  },
+
   // the first browser window has finished initializing
   _onFirstWindowLoaded: function BG__onFirstWindowLoaded(aWindow) {
     TabCrashHandler.init();
@@ -1329,6 +1347,8 @@ BrowserGlue.prototype = {
     this._firstWindowTelemetry(aWindow);
     this._firstWindowLoaded();
 
+    this._collectStartupConditionsTelemetry();
+
     // Set the default favicon size for UI views that use the page-icon protocol.
     PlacesUtils.favicons.setDefaultIconURIPreferredSize(16 * aWindow.devicePixelRatio);
     this._setPrefExpectations();

toolkit/components/startup/nsAppStartup.cpp

@@ -47,6 +47,10 @@
 #if defined(XP_WIN)
 // Prevent collisions with nsAppStartup::GetStartupInfo()
 #  undef GetStartupInfo
+
+#  include <windows.h>
+#elif defined(XP_DARWIN)
+#  include <mach/mach_time.h>
 #endif
 
 #include "mozilla/IOInterposer.h"
@@ -60,6 +64,8 @@ static NS_DEFINE_CID(kAppShellCID, NS_APPSHELL_CID);
 #define kPrefRecentCrashes "toolkit.startup.recent_crashes"
 #define kPrefAlwaysUseSafeMode "toolkit.startup.always_use_safe_mode"
 
+#define kNanosecondsPerSecond 1000000000.0
+
 #if defined(XP_WIN)
 #  include "mozilla/perfprobe.h"
 /**
@@ -541,6 +547,25 @@ nsAppStartup::GetWasRestarted(bool *aResult) {
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsAppStartup::GetSecondsSinceLastOSRestart(int64_t *aResult) {
+#if defined(XP_WIN)
+  *aResult = int64_t(GetTickCount64() / 1000ull);
+  return NS_OK;
+#elif defined(XP_DARWIN)
+  uint64_t absTime = mach_absolute_time();
+  mach_timebase_info_data_t timebaseInfo;
+  mach_timebase_info(&timebaseInfo);
+  double toNanoseconds =
+      double(timebaseInfo.numer) / double(timebaseInfo.denom);
+  *aResult =
+      std::llround(double(absTime) * toNanoseconds / kNanosecondsPerSecond);
+  return NS_OK;
+#else
+  return NS_ERROR_NOT_IMPLEMENTED;
+#endif
+}
+
 NS_IMETHODIMP
 nsAppStartup::SetInterrupted(bool aInterrupted) {
   mInterrupted = aInterrupted;

toolkit/components/startup/public/nsIAppStartup.idl

@@ -156,6 +156,11 @@ interface nsIAppStartup : nsISupports
      */
     readonly attribute boolean wasRestarted;
 
+    /**
+     * The number of seconds since the OS was last rebooted
+     */
+    readonly attribute int64_t secondsSinceLastOSRestart;
+
     /** 
      * Returns an object with main, process, firstPaint, sessionRestored properties.
      * Properties may not be available depending on platform or application

toolkit/components/telemetry/Scalars.yaml

@@ -3589,6 +3589,20 @@ startup:
     record_in_processes:
       - main
 
+  is_cold:
+    bug_numbers:
+      - 1542833
+    description: >
+      Whether or not this startup is the first startup since OS reboot (according to our
+      best guess.)
+    expires: never
+    kind: boolean
+    notification_emails:
+      - dothayer@mozilla.com
+    release_channel_collection: opt-out
+    record_in_processes:
+      - 'main'
+
 script.preloader:
   mainthread_recompile:
     bug_numbers: