Add option to force cache miss

README.md

@@ -59,6 +59,7 @@ These settings are common across all plugins, although different implementations
 | `$(MSBuildCacheMaxConcurrentCacheContentOperations)` | `int` | 64 | The maximum number of cache operations to perform concurrently |
 | `$(MSBuildCacheLocalCacheRootPath)` | `string` | "\MSBuildCache" (in repo's drive root) | Base directory to use for the local cache. |
 | `$(MSBuildCacheLocalCacheSizeInMegabytes)` | `int` | 102400 (100 GB) | The maximum size in megabytes of the local cache |
+| `$(ForceCacheMissPercentage)` | `int` | 0 | Force a cache miss a percentage of the time. Useful for testing to simulate natural cache misses. |
 | `$(MSBuildCacheIgnoredInputPatterns)` | `Glob[]` |  | Files which are part of the repo which should be ignored for cache invalidation |
 | `$(MSBuildCacheIgnoredOutputPatterns)` | `Glob[]` | `*.assets.cache; *assemblyreference.cache` | Files to ignore for output collection into the cache. Note that if output are ignored, the replayed cache entry will not have these files. This should be used for intermediate outputs which are not properly portable |
 | `$(MSBuildCacheIdenticalDuplicateOutputPatterns)` | `Glob[]` | | Files to allow duplicate outputs, with identical content, across projects. Projects which produce files at the same path with differing content will still produce an error. Note: this setting should be used sparingly as it impacts performance |

src/Common.Tests/PluginSettingsTests.cs

@@ -94,6 +94,13 @@ public void LocalCacheSizeInMegabytesSetting()
             pluginSettings => pluginSettings.LocalCacheSizeInMegabytes,
             new[] { 123u, 456u, 789u });
 
+    [TestMethod]
+    public void ForceCacheMissPercentageSetting()
+        => TestBasicSetting(
+            nameof(PluginSettings.ForceCacheMissPercentage),
+            pluginSettings => pluginSettings.ForceCacheMissPercentage,
+            new[] { 0u, 10u, 100u });
+
     private static IEnumerable<object[]> GlobTestData
     {
         get

src/Common/MSBuildCachePluginBase.cs

@@ -11,6 +11,7 @@
 using System.IO;
 using System.Linq;
 using System.Reflection;
+using System.Security.Cryptography;
 using System.Text;
 using System.Text.Json;
 using System.Threading;
@@ -105,7 +106,8 @@ static MSBuildCachePluginBase() =>
         nameof(_fileAccessRepository),
         nameof(_cacheClient),
         nameof(_ignoredOutputPatterns),
-        nameof(_identicalDuplicateOutputPatterns)
+        nameof(_identicalDuplicateOutputPatterns),
+        nameof(Settings)
     )]
     protected bool Initialized { get; private set; }
 
@@ -350,6 +352,26 @@ private async Task<CacheResult> GetCacheResultInnerAsync(BuildRequestData buildR
             return CacheResult.IndicateNonCacheHit(CacheResultType.CacheMiss);
         }
 
+        if (Settings.ForceCacheMissPercentage != 0)
+        {
+            // use a hash of the project id so that it is repeatable
+
+#if NETFRAMEWORK
+            using SHA256 hasher = SHA256.Create();
+            byte[] projectHash = hasher.ComputeHash(Encoding.UTF8.GetBytes(nodeContext.Id));
+#else
+            byte[] projectHash = SHA256.HashData(Encoding.UTF8.GetBytes(nodeContext.Id));
+#endif
+
+            uint hashInt = BitConverter.ToUInt32(projectHash, 0);
+            if ((hashInt % 100) < Settings.ForceCacheMissPercentage)
+            {
+                logger.LogMessage($"Forcing an otherwise 'cache hit' to be a 'cache miss' because of ForceCacheMissPercentage.");
+                Interlocked.Increment(ref _cacheMissCount);
+                return CacheResult.IndicateNonCacheHit(CacheResultType.CacheMiss);
+            }
+        }
+
         CheckForDuplicateOutputs(logger, nodeBuildResult.Outputs, nodeContext);
 
         await FinishNodeAsync(logger, nodeContext, pathSet, nodeBuildResult);

src/Common/PluginSettings.cs

@@ -81,6 +81,8 @@ public string LocalCacheRootPath
 
     public uint LocalCacheSizeInMegabytes { get; init; } = 102400; // 100GB
 
+    public uint ForceCacheMissPercentage { get; init; }
+
     public IReadOnlyCollection<Glob> IgnoredInputPatterns { get; init; } = Array.Empty<Glob>();
 
     public IReadOnlyCollection<Glob> IgnoredOutputPatterns { get; init; } = Array.Empty<Glob>();

src/Common/build/Microsoft.MSBuildCache.Common.targets

@@ -10,6 +10,7 @@
     <MSBuildCacheGlobalPropertiesToIgnore>$(MSBuildCacheGlobalPropertiesToIgnore);MSBuildCacheMaxConcurrentCacheContentOperations</MSBuildCacheGlobalPropertiesToIgnore>
     <MSBuildCacheGlobalPropertiesToIgnore>$(MSBuildCacheGlobalPropertiesToIgnore);MSBuildCacheLocalCacheRootPath</MSBuildCacheGlobalPropertiesToIgnore>
     <MSBuildCacheGlobalPropertiesToIgnore>$(MSBuildCacheGlobalPropertiesToIgnore);MSBuildCacheLocalCacheSizeInMegabytes</MSBuildCacheGlobalPropertiesToIgnore>
+    <MSBuildCacheGlobalPropertiesToIgnore>$(MSBuildCacheGlobalPropertiesToIgnore);MSBuildCacheForceCacheMissPercentage</MSBuildCacheGlobalPropertiesToIgnore>
     <MSBuildCacheGlobalPropertiesToIgnore>$(MSBuildCacheGlobalPropertiesToIgnore);MSBuildCacheIgnoredInputPatterns</MSBuildCacheGlobalPropertiesToIgnore>
     <MSBuildCacheGlobalPropertiesToIgnore>$(MSBuildCacheGlobalPropertiesToIgnore);MSBuildCacheIgnoredOutputPatterns</MSBuildCacheGlobalPropertiesToIgnore>
     <MSBuildCacheGlobalPropertiesToIgnore>$(MSBuildCacheGlobalPropertiesToIgnore);MSBuildCacheIdenticalDuplicateOutputPatterns</MSBuildCacheGlobalPropertiesToIgnore>
@@ -29,6 +30,7 @@
       <MaxConcurrentCacheContentOperations>$(MSBuildCacheMaxConcurrentCacheContentOperations)</MaxConcurrentCacheContentOperations>
       <LocalCacheRootPath>$(MSBuildCacheLocalCacheRootPath)</LocalCacheRootPath>
       <LocalCacheSizeInMegabytes>$(MSBuildCacheLocalCacheSizeInMegabytes)</LocalCacheSizeInMegabytes>
+      <ForceCacheMissPercentage>$(MSBuildCacheForceCacheMissPercentage)</ForceCacheMissPercentage>
       <IgnoredInputPatterns>$(MSBuildCacheIgnoredInputPatterns)</IgnoredInputPatterns>
       <IgnoredOutputPatterns>$(MSBuildCacheIgnoredOutputPatterns)</IgnoredOutputPatterns>
       <IdenticalDuplicateOutputPatterns>$(MSBuildCacheIdenticalDuplicateOutputPatterns)</IdenticalDuplicateOutputPatterns>

src/Local/MSBuildCacheLocalPlugin.cs

@@ -38,7 +38,6 @@ protected override async Task<ICacheClient> CreateCacheClientAsync(PluginLoggerB
 #pragma warning restore CA2000 // Dispose objects before losing scope
         Context context = new(cacheLogger);
 
-
 #pragma warning disable CA2000 // Dispose objects before losing scope. Expected to be disposed by TwoLevelCache
         LocalCache cache = LocalCacheFactory.Create(cacheLogger, Settings.LocalCacheRootPath, Settings.LocalCacheSizeInMegabytes);
 #pragma warning restore CA2000 // Dispose objects before losing scope