Garbage collection optimisations:

- Changed a few IEnumerable instances to IReadOnlyList. This avoids some unnecessary GC allocs that cast the Lists to IEnumerables.
- Moved cdf allocation outside of the loop to avoid unnecessary GC allocation.
- Changed GeneratorImpl to use plain float and int arrays instead of Array during generation. This avoids SetValue performing boxing on the arrays, which eliminates an awful lot of GC allocs.

UnitySDK/Assets/ML-Agents/Scripts/InferenceBrain/GeneratorImpl.cs

@@ -66,14 +66,15 @@ public void Generate(Tensor tensor, int batchSize, Dictionary<Agent, AgentInfo>
         {
             tensor.Shape[0] = batchSize;
             var vecObsSizeT = tensor.Shape[tensor.Shape.Length - 1];
-            tensor.Data = new float[batchSize, vecObsSizeT];
+            var floatArray = new float[batchSize, vecObsSizeT];
+            tensor.Data = floatArray;
             var agentIndex = 0;
             foreach (var agent in agentInfo.Keys)
             {
                 var vectorObs = agentInfo[agent].stackedVectorObservation;
                 for (var j = 0; j < vecObsSizeT; j++)
                 {
-                    tensor.Data.SetValue(vectorObs[j], new int[2] {agentIndex, j});
+                    floatArray[agentIndex, j] = vectorObs[j];
                 }
                 agentIndex++;
             }
@@ -92,7 +93,8 @@ public void Generate(Tensor tensor, int batchSize, Dictionary<Agent, AgentInfo>
         {
             tensor.Shape[0] = batchSize;
             var memorySize = tensor.Shape[tensor.Shape.Length - 1];
-            tensor.Data = new float[batchSize, memorySize];
+            var floatArray = new float[batchSize, memorySize];
+            tensor.Data = floatArray;
             var agentIndex = 0;
             foreach (var agent in agentInfo.Keys)
             {
@@ -108,7 +110,7 @@ public void Generate(Tensor tensor, int batchSize, Dictionary<Agent, AgentInfo>
                     {
                         break;
                     }
-                    tensor.Data.SetValue(memory[j], new int[2] {agentIndex, j});
+                    floatArray[agentIndex, j] = memory[j];
                 }
                 agentIndex++;
             }
@@ -170,14 +172,15 @@ public void Generate(Tensor tensor, int batchSize, Dictionary<Agent, AgentInfo>
         {
             tensor.Shape[0] = batchSize;
             var actionSize = tensor.Shape[tensor.Shape.Length - 1];
-            tensor.Data = new int[batchSize, actionSize];
+            var intArray = new int[batchSize, actionSize];
+            tensor.Data = intArray;
             var agentIndex = 0;
             foreach (var agent in agentInfo.Keys)
             {
                 var pastAction = agentInfo[agent].storedVectorActions;
                 for (var j = 0; j < actionSize; j++)
                 {
-                    tensor.Data.SetValue((int) pastAction[j], new int[2] {agentIndex, j});
+                    intArray[agentIndex, j] = (int) pastAction[j];
                 }
 
                 agentIndex++;
@@ -197,15 +200,16 @@ public void Generate(Tensor tensor, int batchSize, Dictionary<Agent, AgentInfo>
         {
             tensor.Shape[0] = batchSize;
             var maskSize = tensor.Shape[tensor.Shape.Length - 1];
-            tensor.Data = new float[batchSize, maskSize];
+            var floatArray = new float[batchSize, maskSize];
+            tensor.Data = floatArray;
             var agentIndex = 0;
             foreach (var agent in agentInfo.Keys)
             {
                 var maskList = agentInfo[agent].actionMasks;
                 for (var j = 0; j < maskSize; j++)
                 {
                     var isUnmasked = (maskList != null && maskList[j]) ? 0.0f : 1.0f;
-                    tensor.Data.SetValue(isUnmasked, new int[2] {agentIndex, j});
+                    floatArray[agentIndex, j] = isUnmasked;
                 }
                 agentIndex++;
             }

UnitySDK/Assets/ML-Agents/Scripts/InferenceBrain/ModelParamLoader.cs

@@ -49,7 +49,7 @@ private ModelParamLoader(TFSharpInferenceEngine engine, BrainParameters brainPar
         /// Generates the Tensor inputs that are expected to be present in the Model. 
         /// </summary>
         /// <returns>Tensor IEnumerable with the expected Tensor inputs</returns>
-        public IEnumerable<Tensor> GetInputTensors()
+        public IReadOnlyList<Tensor> GetInputTensors()
         {
             return _engine?.InputFeatures();
         }
@@ -58,7 +58,7 @@ public IEnumerable<Tensor> GetInputTensors()
         /// Generates the Tensor outputs that are expected to be present in the Model. 
         /// </summary>
         /// <returns>Tensor IEnumerable with the expected Tensor outputs</returns>
-        public IEnumerable<Tensor> GetOutputTensors()
+        public IReadOnlyList<Tensor> GetOutputTensors()
         {
             var tensorList = new List<Tensor>();
             if (_brainParameters.vectorActionSpaceType == SpaceType.continuous)

UnitySDK/Assets/ML-Agents/Scripts/InferenceBrain/TFSharpInferenceEngine.cs

@@ -195,7 +195,7 @@ private Tensor GetOpMetadata(TFOperation op)
             return t;
         }
 
-        public IEnumerable<Tensor> InputFeatures()
+        public IReadOnlyList<Tensor> InputFeatures()
         {
             List<Tensor> inputs = new List<Tensor>();
             foreach (var op in m_graph.GetEnumerator())

UnitySDK/Assets/ML-Agents/Scripts/InferenceBrain/Utils/Multinomial.cs

@@ -60,6 +60,8 @@ public void Eval(Tensor src, Tensor dst)
                 throw new ArgumentException("Batch size for input and output data is different!");
             }
 
+            float[] cdf = new float[input_data.GetLength(1)];
+
             for (int batch = 0; batch < input_data.GetLength(0); ++batch)
             {
                 // Find the class maximum
@@ -71,7 +73,6 @@ public void Eval(Tensor src, Tensor dst)
 
                 // Sum the log probabilities and compute CDF
                 float sumProb = 0.0f;
-                float[] cdf = new float[input_data.GetLength(1)];
                 for (int cls = 0; cls < input_data.GetLength(1); ++cls)
                 {
                     sumProb += Mathf.Exp(input_data[batch, cls] - maxProb);

UnitySDK/Assets/ML-Agents/Scripts/LearningBrain.cs

@@ -51,8 +51,8 @@ public class LearningBrain : Brain
                  "(This field is not applicable for training).")]
         public InferenceDevice inferenceDevice = InferenceDevice.CPU;
 
-        private IEnumerable<Tensor> _inferenceInputs;
-        private IEnumerable<Tensor> _inferenceOutputs;
+        private IReadOnlyList<Tensor> _inferenceInputs;
+        private IReadOnlyList<Tensor> _inferenceOutputs;
 
         [NonSerialized]
         private bool _isControlled;