Merge pull request microsoft#1849 from tyrielv/async-prefetch

Prefetch in background when cloning if pack indexes are not trusted

Author: tyrielv

GVFS/GVFS.Common/Enlistment.cs

@@ -109,5 +109,18 @@ public virtual GitProcess CreateGitProcess()
         {
             return new GitProcess(this);
         }
+
+        public bool GetTrustPackIndexesConfig()
+        {
+            var gitProcess = this.CreateGitProcess();
+            bool trustPackIndexes = true;
+            if (gitProcess.TryGetFromConfig(GVFSConstants.GitConfig.TrustPackIndexes, forceOutsideEnlistment: false, out var valueString)
+                && bool.TryParse(valueString, out var trustPackIndexesConfig))
+            {
+                trustPackIndexes = trustPackIndexesConfig;
+            }
+
+            return trustPackIndexes;
+        }
     }
 }

GVFS/GVFS.Common/Git/GitObjects.cs

@@ -135,12 +135,7 @@ public virtual bool TryDownloadPrefetchPacks(GitProcess gitProcess, long latestT
                  * pack file and an index file that do not match.
                  * Eventually we will make this the default, but it has a high performance cost for the first prefetch after
                  * cloning a large repository, so it must be explicitly enabled for now. */
-                bool trustPackIndexes = true;
-                if (gitProcess.TryGetFromConfig(GVFSConstants.GitConfig.TrustPackIndexes, forceOutsideEnlistment: false, out var valueString)
-                    && bool.TryParse(valueString, out var trustPackIndexesConfig))
-                {
-                    trustPackIndexes = trustPackIndexesConfig;
-                }
+                bool trustPackIndexes = this.Enlistment.GetTrustPackIndexesConfig();
                 metadata.Add("trustPackIndexes", trustPackIndexes);
 
                 long requestId = HttpRequestor.GetNewRequestId();

GVFS/GVFS/CommandLine/CloneVerb.cs

@@ -215,20 +215,40 @@ public override void Execute()
                 {
                     if (!this.NoPrefetch)
                     {
-                        ReturnCode result = this.Execute<PrefetchVerb>(
-                            enlistment,
-                            verb =>
+                        bool trustPackIndexes = enlistment.GetTrustPackIndexesConfig();
+                        /* If pack indexes are not trusted, the prefetch can take a long time.
+                         * We will run the prefetch command in the background.
+                         */
+                        if (trustPackIndexes)
+                        {
+                            ReturnCode result = this.Execute<PrefetchVerb>(
+                                enlistment,
+                                verb =>
+                                {
+                                    verb.Commits = true;
+                                    verb.SkipVersionCheck = true;
+                                    verb.ResolvedCacheServer = cacheServer;
+                                    verb.ServerGVFSConfig = serverGVFSConfig;
+                                });
+
+                            if (result != ReturnCode.Success)
                             {
-                                verb.Commits = true;
-                                verb.SkipVersionCheck = true;
-                                verb.ResolvedCacheServer = cacheServer;
-                                verb.ServerGVFSConfig = serverGVFSConfig;
-                            });
+                                this.Output.WriteLine("\r\nError during prefetch @ {0}", fullEnlistmentRootPathParameter);
+                                exitCode = (int)result;
+                            }
+                        }
 
-                        if (result != ReturnCode.Success)
+                        else
                         {
-                            this.Output.WriteLine("\r\nError during prefetch @ {0}", fullEnlistmentRootPathParameter);
-                            exitCode = (int)result;
+                            Process.Start(new ProcessStartInfo(
+                                fileName: "gvfs",
+                                arguments: "prefetch --commits")
+                            {
+                                UseShellExecute = true,
+                                WindowStyle = ProcessWindowStyle.Hidden,
+                                WorkingDirectory = enlistment.EnlistmentRoot
+                            });
+                            this.Output.WriteLine("\r\nPrefetch of commit graph has been started as a background process. Git operations involving history may be slower until prefetch has completed.\r\n");
                         }
                     }
 
@@ -247,7 +267,7 @@ public override void Execute()
                                 verb.SkipVersionCheck = true;
                                 verb.ResolvedCacheServer = cacheServer;
                                 verb.DownloadedGVFSConfig = serverGVFSConfig;
-                            });
+                            });
                     }
                 }
                 else