Don't store UsageModel in memory.

As there can be >1 instance of VS running. There is still the
possibility of race conditions here but as they would be unlikely and
the impact would be minimal, I'm tempted to just accept the possibility
rather than make the code more complex.

Author: Steven Kirk

src/GitHub.Exports/Services/UsageTracker.cs

@@ -7,7 +7,6 @@
 using System.Windows.Threading;
 using GitHub.Models;
 using GitHub.Settings;
-using GitHub.VisualStudio;
 using Microsoft.VisualStudio.ComponentModelHost;
 using Microsoft.VisualStudio.Shell;
 using Task = System.Threading.Tasks.Task;
@@ -19,15 +18,13 @@ namespace GitHub.Services
     public class UsageTracker : IUsageTracker
     {
         const string StoreFileName = "ghfvs.usage";
-        //static readonly NLog.Logger log = NLog.LogManager.GetCurrentClassLogger();
         static readonly Calendar cal = CultureInfo.InvariantCulture.Calendar;
 
         readonly IMetricsService client;
         readonly Lazy<IConnectionManager> connectionManager;
         readonly IPackageSettings userSettings;
         readonly DispatcherTimer timer;
         readonly string storePath;
-        UsageStore usage;
 
         [ImportingConstructor]
         public UsageTracker(
@@ -50,7 +47,6 @@ public UsageTracker(
                 Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
                 program.ApplicationName,
                 StoreFileName);
-            this.usage = LoadUsage();
 
             userSettings.PropertyChanged += (s, e) =>
             {
@@ -65,6 +61,7 @@ public UsageTracker(
 
         public void IncrementLaunchCount()
         {
+            var usage = LoadUsage();
             ++usage.Model.NumberOfStartups;
             ++usage.Model.NumberOfStartupsWeek;
             ++usage.Model.NumberOfStartupsMonth;
@@ -73,42 +70,49 @@ public void IncrementLaunchCount()
 
         public void IncrementCloneCount()
         {
+            var usage = LoadUsage();
             ++usage.Model.NumberOfClones;
             SaveUsage(usage);
         }
 
         public void IncrementCreateCount()
         {
+            var usage = LoadUsage();
             ++usage.Model.NumberOfReposCreated;
             SaveUsage(usage);
         }
 
         public void IncrementPublishCount()
         {
+            var usage = LoadUsage();
             ++usage.Model.NumberOfReposPublished;
             SaveUsage(usage);
         }
 
         public void IncrementOpenInGitHubCount()
         {
+            var usage = LoadUsage();
             ++usage.Model.NumberOfOpenInGitHub;
             SaveUsage(usage);
         }
 
         public void IncrementLinkToGitHubCount()
         {
+            var usage = LoadUsage();
             ++usage.Model.NumberOfLinkToGitHub;
             SaveUsage(usage);
         }
 
         public void IncrementCreateGistCount()
         {
+            var usage = LoadUsage();
             ++usage.Model.NumberOfGists;
             SaveUsage(usage);
         }
 
         public void IncrementUpstreamPullRequestCount()
         {
+            var usage = LoadUsage();
             ++usage.Model.NumberOfClones;
             SaveUsage(usage);
         }
@@ -167,6 +171,7 @@ async void TimerTick(object sender, EventArgs e)
                 // launch count but we only submit (and clear) the weekly launch count when we've
                 // transitioned into a new week. We've defined a week by the ISO8601 definition,
                 // i.e. week starting on Monday and ending on Sunday.
+                var usage = LoadUsage();
                 var lastDate = usage.LastUpdated;
                 var currentDate = DateTimeOffset.Now;
                 var includeWeekly = GetIso8601WeekOfYear(lastDate) != GetIso8601WeekOfYear(currentDate);
@@ -175,8 +180,8 @@ async void TimerTick(object sender, EventArgs e)
                 // Only send stats once a day.
                 if (lastDate.Date != currentDate.Date)
                 {
-                    await SendUsage(includeWeekly, includeMonthly);
-                    ClearCounters(includeWeekly, includeMonthly);
+                    await SendUsage(usage.Model, includeWeekly, includeMonthly);
+                    ClearCounters(usage.Model, includeWeekly, includeMonthly);
                     usage.LastUpdated = DateTimeOffset.Now.UtcDateTime;
                     SaveUsage(usage);
                 }
@@ -187,23 +192,23 @@ async void TimerTick(object sender, EventArgs e)
             }
         }
 
-        async Task SendUsage(bool weekly, bool monthly)
+        async Task SendUsage(UsageModel usage, bool weekly, bool monthly)
         {
             Debug.Assert(client != null, "SendUsage should not be called when there is no IMetricsService");
 
             var connectionManager = this.connectionManager.Value;
 
             if (connectionManager.Connections.Any(x => x.HostAddress.IsGitHubDotCom()))
             {
-                usage.Model.IsGitHubUser = true;
+                usage.IsGitHubUser = true;
             }
 
             if (connectionManager.Connections.Any(x => !x.HostAddress.IsGitHubDotCom()))
             {
-                usage.Model.IsEnterpriseUser = true;
+                usage.IsEnterpriseUser = true;
             }
 
-            var model = usage.Model.Clone(weekly, monthly);
+            var model = usage.Clone(weekly, monthly);
             await client.PostUsage(model);
         }
 
@@ -223,23 +228,23 @@ static int GetIso8601WeekOfYear(DateTimeOffset time)
             return cal.GetWeekOfYear(time.UtcDateTime, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
         }
 
-        void ClearCounters(bool weekly, bool monthly)
+        static void ClearCounters(UsageModel usage, bool weekly, bool monthly)
         {
-            usage.Model.NumberOfStartups = 0;
-            usage.Model.NumberOfClones = 0;
-            usage.Model.NumberOfReposCreated = 0;
-            usage.Model.NumberOfReposPublished = 0;
-            usage.Model.NumberOfGists = 0;
-            usage.Model.NumberOfOpenInGitHub = 0;
-            usage.Model.NumberOfLinkToGitHub = 0;
-            usage.Model.NumberOfLogins = 0;
-            usage.Model.NumberOfUpstreamPullRequests = 0;
+            usage.NumberOfStartups = 0;
+            usage.NumberOfClones = 0;
+            usage.NumberOfReposCreated = 0;
+            usage.NumberOfReposPublished = 0;
+            usage.NumberOfGists = 0;
+            usage.NumberOfOpenInGitHub = 0;
+            usage.NumberOfLinkToGitHub = 0;
+            usage.NumberOfLogins = 0;
+            usage.NumberOfUpstreamPullRequests = 0;
 
             if (weekly)
-                usage.Model.NumberOfStartupsWeek = 0;
+                usage.NumberOfStartupsWeek = 0;
 
             if (monthly)
-                usage.Model.NumberOfStartupsMonth = 0;
+                usage.NumberOfStartupsMonth = 0;
         }
 
         class UsageStore