Use swift-atomics (#1453)

Motivation:

NIO deprecated its atomics in apple/swift-nio#2204.

Modifications:

- Use swift-atomics in the `QPSBenchmark` sub-package
- Use a lock in the one test which used `NIOAtomic`

Result:

Not using deprecated code.

Performance/QPSBenchmark/Package.swift

@@ -27,6 +27,7 @@ let package = Package(
     .package(url: "https://github.com/apple/swift-nio.git", from: "2.32.0"),
     .package(url: "https://github.com/apple/swift-log.git", from: "1.4.0"),
     .package(url: "https://github.com/apple/swift-argument-parser.git", from: "1.0.0"),
+    .package(url: "https://github.com/apple/swift-atomics.git", from: "1.0.2"),
     .package(
       url: "https://github.com/swift-server/swift-service-lifecycle.git",
       from: "1.0.0-alpha"
@@ -42,6 +43,7 @@ let package = Package(
       name: "QPSBenchmark",
       dependencies: [
         .product(name: "GRPC", package: "grpc-swift"),
+        .product(name: "Atomics", package: "swift-atomics"),
         .product(name: "NIOCore", package: "swift-nio"),
         .product(name: "NIOPosix", package: "swift-nio"),
         .product(name: "NIOConcurrencyHelpers", package: "swift-nio"),

Performance/QPSBenchmark/Sources/QPSBenchmark/Runtime/AsyncClient.swift

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+import Atomics
 import BenchmarkUtils
 import Foundation
 import GRPC
@@ -168,8 +169,8 @@ final class AsyncQPSClient<RequestMakerType: RequestMaker>: QPSClient {
     /// Succeeds after a stop has been requested and all outstanding requests have completed.
     private var stopComplete: EventLoopPromise<Void>
 
-    private let running: NIOAtomic<Bool> = .makeAtomic(value: false)
-    private let outstanding: NIOAtomic<Int> = .makeAtomic(value: 0)
+    private let running = ManagedAtomic<Bool>(false)
+    private let outstanding = ManagedAtomic<Int>(0)
 
     private var requestMaker: RequestMakerType
 
@@ -211,15 +212,20 @@ final class AsyncQPSClient<RequestMakerType: RequestMaker>: QPSClient {
       // - when a request finishes it will either start a new request or decrement the
       //   the atomic counter (if we've been told to stop)
       // - if the counter drops to zero we're finished.
-      let exchangedRunning = self.running.compareAndExchange(expected: false, desired: true)
-      precondition(exchangedRunning, "launchRequests should only be called once")
+      let exchangedRunning = self.running.compareExchange(
+        expected: false,
+        desired: true,
+        ordering: .relaxed
+      )
+      precondition(exchangedRunning.exchanged, "launchRequests should only be called once")
 
       // We only decrement the outstanding count when running has been changed back to false.
-      let exchangedOutstanding = self.outstanding.compareAndExchange(
+      let exchangedOutstanding = self.outstanding.compareExchange(
         expected: 0,
-        desired: self.maxPermittedOutstandingRequests
+        desired: self.maxPermittedOutstandingRequests,
+        ordering: .relaxed
       )
-      precondition(exchangedOutstanding, "launchRequests should only be called once")
+      precondition(exchangedOutstanding.exchanged, "launchRequests should only be called once")
 
       for _ in 0 ..< self.maxPermittedOutstandingRequests {
         self.requestMaker.makeRequest().whenComplete { _ in
@@ -229,11 +235,11 @@ final class AsyncQPSClient<RequestMakerType: RequestMaker>: QPSClient {
     }
 
     private func makeRequest() {
-      if self.running.load() {
+      if self.running.load(ordering: .relaxed) {
         self.requestMaker.makeRequest().whenComplete { _ in
           self.makeRequest()
         }
-      } else if self.outstanding.sub(1) == 1 {
+      } else if self.outstanding.loadThenWrappingDecrement(ordering: .relaxed) == 1 {
         self.stopIsComplete()
       } // else we're no longer running but not all RPCs have finished.
     }
@@ -260,7 +266,7 @@ final class AsyncQPSClient<RequestMakerType: RequestMaker>: QPSClient {
     /// - returns: A future which can be waited on to signal when all activity has ceased.
     func stop() -> EventLoopFuture<Void> {
       self.requestMaker.requestStop()
-      self.running.store(false)
+      self.running.store(false, ordering: .relaxed)
       return self.stopComplete.futureResult
     }
   }

Tests/GRPCTests/StreamResponseHandlerRetainCycleTests.swift

@@ -57,10 +57,19 @@ final class StreamResponseHandlerRetainCycleTests: GRPCTestCase {
 
   func testHandlerClosureIsReleasedOnceStreamEnds() {
     final class Counter {
-      private let atomic = NIOAtomic.makeAtomic(value: 0)
-      func increment() { self.atomic.add(1) }
+      private let lock = Lock()
+      private var _value = 0
+
+      func increment() {
+        self.lock.withLockVoid {
+          self._value += 1
+        }
+      }
+
       var value: Int {
-        self.atomic.load()
+        return self.lock.withLock {
+          self._value
+        }
       }
     }