Merge pull request #342 from ogxd/32bit-collisions

Change MetricFamily dictionary key from 32 to 64 bits hash to reduce collisions

Author: phnx47

src/Prometheus.Client/LabelsHelper.cs

@@ -61,19 +61,19 @@ int GetTupleSize(Type tupleType)
 #endif
     }
 
-    public static int GetHashCode<TTuple>(TTuple values)
+    public static int GetHashCode<TTuple>(TTuple values, int seed = 0)
 #if NET6_0_OR_GREATER
         where TTuple : struct, ITuple, IEquatable<TTuple>
 #else
         where TTuple : struct, IEquatable<TTuple>
 #endif
     {
-        return TupleHelper<TTuple>.GetTupleHashCode(values);
+        return TupleHelper<TTuple>.GetTupleHashCode(values, seed);
     }
 
-    public static int GetHashCode(IReadOnlyList<string> values)
+    public static int GetHashCode(IReadOnlyList<string> values, int seed = 0)
     {
-        var result = 0;
+        var result = seed;
 
         // ReSharper disable once ForCanBeConvertedToForeach
         // do not use for-each here, it allocates which is easy to avoid by for loop
@@ -260,9 +260,9 @@ public static string[] ToArray(TTuple values)
             });
         }
 
-        public static int GetTupleHashCode(TTuple values)
+        public static int GetTupleHashCode(TTuple values, int seed)
         {
-            return _hashCodeReducer(values, 0, (item, _, aggregated) =>
+            return _hashCodeReducer(values, seed, (item, _, aggregated) =>
             {
                 if (item == null)
                     throw new ArgumentException("Label value cannot be empty");

src/Prometheus.Client/MetricFamily.cs

@@ -24,7 +24,7 @@ public sealed class MetricFamily<TMetric, TImplementation, TLabels, TConfig> : I
     private readonly IReadOnlyList<string> _metricNames;
     private readonly Func<TConfig, IReadOnlyList<string>, TImplementation> _instanceFactory;
     private readonly Lazy<TImplementation> _unlabelled;
-    private readonly ConcurrentDictionary<int, TImplementation> _labelledMetrics;
+    private readonly ConcurrentDictionary<MetricKey, TImplementation> _labelledMetrics;
 
     public MetricFamily(TConfig configuration, MetricType metricType, Func<TConfig, IReadOnlyList<string>, TImplementation> instanceFactory)
     {
@@ -35,7 +35,7 @@ public MetricFamily(TConfig configuration, MetricType metricType, Func<TConfig,
         _unlabelled = new Lazy<TImplementation>(() => _instanceFactory(_configuration, default));
         LabelNames = LabelsHelper.FromArray<TLabels>(configuration.LabelNames);
         if (configuration.LabelNames.Count > 0)
-            _labelledMetrics = new ConcurrentDictionary<int, TImplementation>();
+            _labelledMetrics = new ConcurrentDictionary<MetricKey, TImplementation>();
     }
 
     public string Name => _configuration.Name;
@@ -64,7 +64,7 @@ TMetric IMetricFamily<TMetric>.WithLabels(params string[] labels)
         if (labels.Length != _configuration.LabelNames.Count)
             throw new ArgumentException("Wrong number of labels");
 
-        var key = LabelsHelper.GetHashCode(labels);
+        var key = new MetricKey(labels);
 
         if (_labelledMetrics.TryGetValue(key, out var metric))
         {
@@ -83,7 +83,7 @@ TMetric IMetricFamily<TMetric>.RemoveLabelled(params string[] labels)
         if (labels.Length != _configuration.LabelNames.Count)
             throw new ArgumentException("Wrong number of labels");
 
-        var key = LabelsHelper.GetHashCode(labels);
+        var key = new MetricKey(labels);
         _labelledMetrics.TryRemove(key, out var removed);
 
         return removed;
@@ -94,7 +94,7 @@ public TMetric WithLabels(TLabels labels)
         if (_labelledMetrics == null)
             throw new InvalidOperationException("Metric family does not have any labels");
 
-        var key = LabelsHelper.GetHashCode(labels);
+        var key = new MetricKey(labels);
 
         if (_labelledMetrics.TryGetValue(key, out var metric))
         {
@@ -110,7 +110,7 @@ public TMetric RemoveLabelled(TLabels labels)
         if (_labelledMetrics == null)
             throw new InvalidOperationException("Metric family does not have any labels");
 
-        var key = LabelsHelper.GetHashCode(labels);
+        var key = new MetricKey(labels);
         _labelledMetrics.TryRemove(key, out var removed);
 
         return removed;
@@ -148,4 +148,32 @@ private IEnumerable<KeyValuePair<IReadOnlyList<string>, TMetric>> EnumerateLabel
         foreach (var labelled in _labelledMetrics)
             yield return new KeyValuePair<IReadOnlyList<string>, TMetric>(labelled.Value.LabelValues, labelled.Value);
     }
+
+    private readonly struct MetricKey : IEquatable<MetricKey>
+    {
+        private readonly int _hash1;
+        private readonly int _hash2;
+
+        public MetricKey(TLabels labels)
+        {
+            _hash1 = LabelsHelper.GetHashCode(labels, 0);
+            _hash2 = LabelsHelper.GetHashCode(labels, 42);
+        }
+
+        public MetricKey(params string[] labels)
+        {
+            _hash1 = LabelsHelper.GetHashCode(labels, 0);
+            _hash2 = LabelsHelper.GetHashCode(labels, 42);
+        }
+
+        public override int GetHashCode()
+        {
+            return _hash1;
+        }
+
+        public bool Equals(MetricKey other)
+        {
+            return _hash1 == other._hash1 && _hash2 == other._hash2;
+        }
+    }
 }