fix: auto-generate jobid between benchmark runs

Author: filzrev

src/BenchmarkDotNet/Jobs/JobIdGenerator.cs

@@ -10,12 +10,23 @@ public static string GenerateRandomId(Job job)
             string presentation = CharacteristicSetPresenter.Display.ToPresentation(job);
             if (presentation == "")
                 return "DefaultJob";
-            int seed = presentation.GetHashCode();
+            int seed = GetStableHashCode(presentation);
             var random = new Random(seed);
             string id = "";
             for (int i = 0; i < 6; i++)
-                id += (char) ('A' + random.Next(26));
+                id += (char)('A' + random.Next(26));
             return "Job-" + id;
         }
+
+        // Compute string hash value with DJB2 algorithm.
+        private static int GetStableHashCode(string value)
+        {
+            uint hash = 5381;
+            foreach (char c in value)
+            {
+                hash = ((hash << 5) + hash) + c; // hash * 32 + hash + c
+            }
+            return unchecked((int)hash);
+        }
     }
 }

tests/BenchmarkDotNet.Tests/Configs/ImmutableConfigTests.cs

@@ -312,7 +312,7 @@ public void WhenTwoConfigsAreAddedTheMutatorJobsAreAppliedToDefaultJobIfCustomDe
                 Assert.Equal(warmupCount, mergedJob.Run.WarmupCount);
                 Assert.False(mergedJob.Meta.IsDefault); // after the merge the "child" job becomes a standard job
                 Assert.False(mergedJob.Meta.IsMutator); // after the merge the "child" job becomes a standard job
-                Assert.Single(mergedJob.GetCharacteristicsWithValues(), changedCharacteristic => ReferenceEquals(changedCharacteristic, Jobs.RunMode.WarmupCountCharacteristic));
+                Assert.Single(mergedJob.GetCharacteristicsWithValues(), changedCharacteristic => ReferenceEquals(changedCharacteristic, BenchmarkDotNet.Jobs.RunMode.WarmupCountCharacteristic));
             }
         }
 

tests/BenchmarkDotNet.Tests/Jobs/JobIdGeneratorTests.cs

@@ -0,0 +1,27 @@
+using BenchmarkDotNet.Environments;
+using BenchmarkDotNet.Jobs;
+using BenchmarkDotNet.Toolchains.CsProj;
+using Xunit;
+
+namespace BenchmarkDotNet.Tests.Jobs;
+
+public class JobIdGeneratorTests
+{
+    [Theory]
+    [MemberData(nameof(GetTheoryData), DisableDiscoveryEnumeration = true)]
+    public void AutoGenerateJobId(string expectedId, Job job)
+    {
+        // Act
+        var result = job.ResolvedId;
+
+        // Assert
+        Assert.Equal(expectedId, result);
+    }
+
+    public static TheoryData<string, Job> GetTheoryData() => new TheoryData<string, Job>()
+    {
+        {"Job-OOTPKI", Job.Default.WithToolchain(CsProjCoreToolchain.NetCoreApp80) },
+        {"Job-QAODSR", Job.Default.WithToolchain(CsProjCoreToolchain.NetCoreApp90) },
+        {"Job-KHMDUZ", Job.Default.WithToolchain(CsProjCoreToolchain.NetCoreApp80).WithRuntime(CoreRuntime.Core80) },
+    };
+}