Merge pull request #5728 from krwq/2017-02-15-attempt-to-fix-intermittent-failures

Attempt to fix intermittent failures with ...CLIRetriesLaunchingTheCommandForAtLeastOneSecond

src/Microsoft.DotNet.Cli.Utils/CommandResolution/ProjectToolsCommandResolver.cs

@@ -5,12 +5,15 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 using Microsoft.DotNet.Tools.Common;
 using Microsoft.Extensions.DependencyModel;
 using NuGet.Configuration;
 using NuGet.Frameworks;
 using NuGet.ProjectModel;
 using NuGet.Versioning;
+using ConcurrencyUtilities = NuGet.Common.ConcurrencyUtilities;
 
 namespace Microsoft.DotNet.Cli.Utils
 {
@@ -220,6 +223,15 @@ namespace Microsoft.DotNet.Cli.Utils
             return null;
         }
 
+
+        private static async Task<bool> FileExistsWithLock(string path)
+        {
+            return await ConcurrencyUtilities.ExecuteWithFileLockedAsync(
+                path, 
+                lockedToken => Task.FromResult(File.Exists(path)),
+                CancellationToken.None);
+        }
+
         private bool TryGetToolLockFile(
             SingleProjectInfo toolLibrary,
             string nugetPackagesRoot,
@@ -228,7 +240,7 @@ namespace Microsoft.DotNet.Cli.Utils
             lockFile = null;
             var lockFilePath = GetToolLockFilePath(toolLibrary, nugetPackagesRoot);
 
-            if (!File.Exists(lockFilePath))
+            if (!FileExistsWithLock(lockFilePath).Result)
             {
                 return false;
             }

src/Microsoft.DotNet.Cli.Utils/Extensions/LockFileFormatExtensions.cs

@@ -20,18 +20,18 @@ namespace Microsoft.DotNet.Cli.Utils
 
         public static async Task<LockFile> ReadWithLock(this LockFileFormat subject, string path)
         {
-            if(!File.Exists(path))
-            {
-                throw new GracefulException(string.Join(
-                    Environment.NewLine,
-                    string.Format(LocalizableStrings.FileNotFound, path),
-                    LocalizableStrings.ProjectNotRestoredOrRestoreFailed));
-            }
-
             return await ConcurrencyUtilities.ExecuteWithFileLockedAsync(
                 path, 
                 lockedToken =>
                 {
+                    if (!File.Exists(path))
+                    {
+                        throw new GracefulException(string.Join(
+                            Environment.NewLine,
+                            string.Format(LocalizableStrings.FileNotFound, path),
+                            LocalizableStrings.ProjectNotRestoredOrRestoreFailed));
+                    }
+                    
                     var lockFile = FileAccessRetrier.RetryOnFileAccessFailure(() => subject.Read(path));
 
                     return lockFile;