Addressing concurrency exceptions when incrementing the download count.

.gitignore

@@ -150,6 +150,7 @@ publish/
 # but database connection strings (with potential passwords) will be unencrypted
 *.pubxml
 *.publishproj
+ServiceDependencies/
 
 # Microsoft Azure Web App publish settings. Comment the next line if you want to
 # checkin your Azure Web App publish settings, but sensitive information contained

src/BaGet.Core/BaGet.Core.csproj

@@ -2,7 +2,7 @@
 
  <PropertyGroup>
  <TargetFramework>netstandard2.0</TargetFramework>
-
+ <LangVersion>8</LangVersion>
  <PackageTags>NuGet</PackageTags>
  <Description>The core libraries that power BaGet.</Description>
  </PropertyGroup>

src/BaGet.Core/Entities/IContext.cs

@@ -1,11 +1,12 @@
+using System;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Infrastructure;
 
 namespace BaGet.Core
 {
- public interface IContext
+ public interface IContext : IDisposable
  {
  DatabaseFacade Database { get; }
 

src/BaGet.Core/Entities/NullContext.cs

@@ -28,5 +28,10 @@ public Task<int> SaveChangesAsync(CancellationToken cancellationToken)
  {
  throw new NotImplementedException();
  }
+
+ public void Dispose()
+ {
+ GC.SuppressFinalize(this);
+ }
  }
 }

src/BaGet.Core/Extensions/DependencyInjectionExtensions.Providers.cs

@@ -72,10 +72,10 @@ public static bool HasStorageType(this IConfiguration config, string value)
  Action<IServiceProvider, DbContextOptionsBuilder> configureContext)
  where TContext : DbContext, IContext
  {
- services.TryAddScoped<IContext>(provider => provider.GetRequiredService<TContext>());
+ services.TryAddTransient<IContext>(provider => provider.GetRequiredService<TContext>());
  services.TryAddTransient<IPackageDatabase>(provider => provider.GetRequiredService<PackageDatabase>());
 
- services.AddDbContext<TContext>(configureContext);
+ services.AddDbContext<TContext>(configureContext, contextLifetime: ServiceLifetime.Transient);
 
  services.AddProvider<IContext>((provider, config) =>
  {

src/BaGet.Core/Extensions/DependencyInjectionExtensions.cs

@@ -144,7 +144,7 @@ private static void AddDefaultProviders(this IServiceCollection services)
 
  private static void AddFallbackServices(this IServiceCollection services)
  {
- services.TryAddScoped<IContext, NullContext>();
+ services.TryAddTransient<IContext, NullContext>();
 
  // BaGet's services have multiple implementations that live side-by-side.
  // The application will choose the implementation using one of two ways:

src/BaGet.Core/PackageDatabase.cs

@@ -10,41 +10,45 @@ namespace BaGet.Core
 {
  public class PackageDatabase : IPackageDatabase
  {
- private readonly IContext _context;
+ private readonly Func<IContext> _newContext;
 
- public PackageDatabase(IContext context)
+ public PackageDatabase(Func<IContext> newContext)
  {
- _context = context ?? throw new ArgumentNullException(nameof(context));
+ _newContext = newContext ?? throw new ArgumentNullException(nameof(newContext));
  }
 
  public async Task<PackageAddResult> AddAsync(Package package, CancellationToken cancellationToken)
  {
+ using var context = _newContext();
+
  try
  {
- _context.Packages.Add(package);
-
- await _context.SaveChangesAsync(cancellationToken);
-
+ context.Packages.Add(package);
+ await context.SaveChangesAsync(cancellationToken);
  return PackageAddResult.Success;
  }
  catch (DbUpdateException e)
- when (_context.IsUniqueConstraintViolationException(e))
+ when (context.IsUniqueConstraintViolationException(e))
  {
  return PackageAddResult.PackageAlreadyExists;
  }
  }
 
  public async Task<bool> ExistsAsync(string id, CancellationToken cancellationToken)
  {
- return await _context
+ using var context = _newContext();
+
+ return await context
  .Packages
  .Where(p => p.Id == id)
  .AnyAsync(cancellationToken);
  }
 
  public async Task<bool> ExistsAsync(string id, NuGetVersion version, CancellationToken cancellationToken)
  {
- return await _context
+ using var context = _newContext();
+
+ return await context
  .Packages
  .Where(p => p.Id == id)
  .Where(p => p.NormalizedVersionString == version.ToNormalizedString())
@@ -53,7 +57,9 @@ public async Task<bool> ExistsAsync(string id, NuGetVersion version, Cancellatio
 
  public async Task<IReadOnlyList<Package>> FindAsync(string id, bool includeUnlisted, CancellationToken cancellationToken)
  {
- var query = _context.Packages
+ using var context = _newContext();
+
+ var query = context.Packages
  .Include(p => p.Dependencies)
  .Include(p => p.PackageTypes)
  .Include(p => p.TargetFrameworks)
@@ -73,7 +79,9 @@ public async Task<IReadOnlyList<Package>> FindAsync(string id, bool includeUnlis
  bool includeUnlisted,
  CancellationToken cancellationToken)
  {
- var query = _context.Packages
+ using var context = _newContext();
+
+ var query = context.Packages
  .Include(p => p.Dependencies)
  .Include(p => p.TargetFrameworks)
  .Where(p => p.Id == id)
@@ -99,26 +107,27 @@ public Task<bool> RelistPackageAsync(string id, NuGetVersion version, Cancellati
 
  public async Task AddDownloadAsync(string id, NuGetVersion version, CancellationToken cancellationToken)
  {
- await TryUpdatePackageAsync(id, version, p => p.Downloads += 1, cancellationToken);
+ await TryUpdatePackageWithConcurrencyRetryAsync(id, version, p => p.Downloads += 1, cancellationToken);
  }
 
  public async Task<bool> HardDeletePackageAsync(string id, NuGetVersion version, CancellationToken cancellationToken)
  {
- var package = await _context.Packages
+ using var context = _newContext();
+
+ var package = await context.Packages
  .Where(p => p.Id == id)
  .Where(p => p.NormalizedVersionString == version.ToNormalizedString())
  .Include(p => p.Dependencies)
  .Include(p => p.TargetFrameworks)
  .FirstOrDefaultAsync(cancellationToken);
 
- if (package == null)
+ if (package is null)
  {
  return false;
  }
 
- _context.Packages.Remove(package);
- await _context.SaveChangesAsync(cancellationToken);
-
+ context.Packages.Remove(package);
+ await context.SaveChangesAsync(cancellationToken);
  return true;
  }
 
@@ -128,20 +137,45 @@ public async Task<bool> HardDeletePackageAsync(string id, NuGetVersion version,
  Action<Package> action,
  CancellationToken cancellationToken)
  {
- var package = await _context.Packages
+ using var context = _newContext();
+
+ var package = await context.Packages
  .Where(p => p.Id == id)
  .Where(p => p.NormalizedVersionString == version.ToNormalizedString())
  .FirstOrDefaultAsync();
 
- if (package != null)
+ if (package is null)
  {
- action(package);
- await _context.SaveChangesAsync(cancellationToken);
-
- return true;
+ return false;
  }
 
- return false;
+ action(package);
+ await context.SaveChangesAsync(cancellationToken);
+ return true;
+ }
+
+ private async Task<bool> TryUpdatePackageWithConcurrencyRetryAsync(
+ string id,
+ NuGetVersion version,
+ Action<Package> action,
+ CancellationToken cancellationToken)
+ {
+ var attempts = 0;
+ while (true)
+ {
+ try
+ {
+ return await TryUpdatePackageAsync(id, version, action, cancellationToken);
+ }
+ catch (DbUpdateConcurrencyException)
+ {
+ attempts++;
+ if (attempts >= 5)
+ {
+ throw;
+ }
+ }
+ }
  }
  }
 }

src/BaGet/Startup.cs

@@ -43,7 +43,8 @@ public void ConfigureServices(IServiceCollection services)
  // You can swap between implementations of subsystems like storage and search using BaGet's configuration.
  // Each subsystem's implementation has a provider that reads the configuration to determine if it should be
  // activated. BaGet will run through all its providers until it finds one that is active.
- services.AddScoped(DependencyInjectionExtensions.GetServiceFromProviders<IContext>);
+ services.AddTransient(DependencyInjectionExtensions.GetServiceFromProviders<IContext>);
+ services.AddSingleton<Func<IContext>>(s => () => s.GetService<IContext>());
  services.AddTransient(DependencyInjectionExtensions.GetServiceFromProviders<IStorageService>);
  services.AddTransient(DependencyInjectionExtensions.GetServiceFromProviders<IPackageDatabase>);
  services.AddTransient(DependencyInjectionExtensions.GetServiceFromProviders<ISearchService>);

tests/BaGet.Core.Tests/Metadata/RegistrationBuilderTests.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Moq;
@@ -60,6 +61,7 @@ private Package GetTestPackage(string packageId, string version)
  PackageTypes = new List<PackageType> { new PackageType { Name = "test" } },
  Dependencies = new List<PackageDependency> { },
  Version = new NuGetVersion(version),
+ Published = DateTimeOffset.MinValue.UtcDateTime
  };
  }
  }

tests/BaGet.Core.Tests/Services/PackageDatabaseTests.cs

@@ -197,7 +197,7 @@ public class FactsBase
  public FactsBase()
  {
  _context = new Mock<IContext>();
- _target = new PackageDatabase(_context.Object);
+ _target = new PackageDatabase(_context.Object, () => new Mock<IContext>().Object);
  }
  }
  }