Add serial pool benchmark (#550)

Author: fabianfett

Benchmarks/Benchmarks/ConnectionPoolBenchmarks/ConnectionPoolBenchmarks.swift

@@ -3,7 +3,7 @@ import _ConnectionPoolTestUtils
 import Benchmark
 
 let benchmarks: @Sendable () -> Void = {
-    Benchmark("Minimal benchmark", configuration: .init(scalingFactor: .kilo)) { benchmark in
+    Benchmark("Lease/Release 1k requests: 50 parallel", configuration: .init(scalingFactor: .kilo)) { benchmark in
         let clock = MockClock()
         let factory = MockConnectionFactory<MockClock>(autoMaxStreams: 1)
         var configuration = ConnectionPoolConfiguration()
@@ -28,6 +28,8 @@ let benchmarks: @Sendable () -> Void = {
 
             let sequential = benchmark.scaledIterations.upperBound / configuration.maximumConnectionSoftLimit
 
+            benchmark.startMeasurement()
+
             for parallel in 0..<configuration.maximumConnectionSoftLimit {
                 taskGroup.addTask {
                     for _ in 0..<sequential {
@@ -45,6 +47,52 @@ let benchmarks: @Sendable () -> Void = {
             for i in 0..<configuration.maximumConnectionSoftLimit {
                 await taskGroup.next()
             }
+
+            benchmark.stopMeasurement()
+
+            taskGroup.cancelAll()
+        }
+    }
+
+    Benchmark("Lease/Release 1k requests: sequential", configuration: .init(scalingFactor: .kilo)) { benchmark in
+        let clock = MockClock()
+        let factory = MockConnectionFactory<MockClock>(autoMaxStreams: 1)
+        var configuration = ConnectionPoolConfiguration()
+        configuration.maximumConnectionSoftLimit = 50
+        configuration.maximumConnectionHardLimit = 50
+
+        let pool = ConnectionPool(
+            configuration: configuration,
+            idGenerator: ConnectionIDGenerator(),
+            keepAliveBehavior: MockPingPongBehavior(keepAliveFrequency: nil, connectionType: MockConnection.self),
+            observabilityDelegate: NoOpConnectionPoolMetrics(connectionIDType: MockConnection.ID.self),
+            clock: clock
+        ) {
+            try await factory.makeConnection(id: $0, for: $1)
+        }
+
+        await withTaskGroup { taskGroup in
+
+            taskGroup.addTask {
+                await pool.run()
+            }
+
+            let sequential = benchmark.scaledIterations.upperBound / configuration.maximumConnectionSoftLimit
+
+            benchmark.startMeasurement()
+
+            for _ in benchmark.scaledIterations {
+                do {
+                    try await pool.withConnection { connection in
+                        blackHole(connection)
+                    }
+                } catch {
+                    fatalError()
+                }
+            }
+
+            benchmark.stopMeasurement()
+
             taskGroup.cancelAll()
         }
     }