[PM-1646] Add thread safety to migration process (#2453)

* Make migration process thread safe

* tweaks

src/Core/Abstractions/IStateMigrationService.cs

@@ -4,7 +4,6 @@ namespace Bit.Core.Abstractions
 {
     public interface IStateMigrationService
     {
-        Task<bool> NeedsMigration();
+        Task MigrateIfNeededAsync();
-        Task Migrate();
     }
 }

src/Core/Services/StateMigrationService.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 using Bit.Core.Abstractions;
 using Bit.Core.Enums;
@@ -17,6 +18,7 @@ namespace Bit.Core.Services
         private readonly IStorageService _preferencesStorageService;
         private readonly IStorageService _liteDbStorageService;
         private readonly IStorageService _secureStorageService;
+        private readonly SemaphoreSlim _semaphore;
 
         private enum Storage
         {
@@ -31,9 +33,27 @@ namespace Bit.Core.Services
             _liteDbStorageService = liteDbStorageService;
             _preferencesStorageService = preferenceStorageService;
             _secureStorageService = secureStorageService;
+
+            _semaphore = new SemaphoreSlim(1);
         }
 
-        public async Task<bool> NeedsMigration()
+        public async Task MigrateIfNeededAsync()
+        {
+            await _semaphore.WaitAsync();
+            try
+            {
+                if (await IsMigrationNeededAsync())
+                {
+                    await PerformMigrationAsync();
+                }
+            }
+            finally
+            {
+                _semaphore.Release();
+            }
+        }
+
+        private async Task<bool> IsMigrationNeededAsync()
         {
             var lastVersion = await GetLastStateVersionAsync();
             if (lastVersion == 0)
@@ -45,7 +65,7 @@ namespace Bit.Core.Services
             return lastVersion < StateVersion;
         }
 
-        public async Task Migrate()
+        private async Task PerformMigrationAsync()
         {
             var lastVersion = await GetLastStateVersionAsync();
             switch (lastVersion)

src/Core/Services/StateService.cs

@@ -1537,11 +1537,8 @@ namespace Bit.Core.Services
         {
             if (!_migrationChecked)
             {
-                var migrationService = ServiceContainer.Resolve<IStateMigrationService>("stateMigrationService");
+                var migrationService = ServiceContainer.Resolve<IStateMigrationService>();
-                if (await migrationService.NeedsMigration())
+                await migrationService.MigrateIfNeededAsync();
-                {
-                    await migrationService.Migrate();
-                }
                 _migrationChecked = true;
             }