From a6466bfcacca3756565e3579898ea4ba0455e453 Mon Sep 17 00:00:00 2001
From: Brandon Sneed <brandon@redf.net>
Date: Tue, 27 Jun 2023 11:08:24 -0700
Subject: [PATCH 1/2] Refactored Atomic implementation to avoid TSan warnings

---
 Sources/Segment/Utilities/Atomic.swift        | 30 ++++++++-----------
 .../Policies/CountBasedFlushPolicy.swift      |  2 +-
 2 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/Sources/Segment/Utilities/Atomic.swift b/Sources/Segment/Utilities/Atomic.swift
index ab4e8c87..fe39dff7 100644
--- a/Sources/Segment/Utilities/Atomic.swift
+++ b/Sources/Segment/Utilities/Atomic.swift
@@ -7,29 +7,25 @@
 
 import Foundation
 
+// NOTE: Revised from previous implementation which used a struct and NSLock's.
+// Thread Sanitizer was *correctly* capturing this issue, which was a little obscure
+// given the property wrapper PLUS the semantics of a struct.  Moving to `class`
+// removes the semantics problem and lets TSan approve of what's happening.
+//
+// Additionally, moving to a lock free version is just desirable, so moved to a queue.
+//
+
 @propertyWrapper
-public struct Atomic<T> {
-    var value: T
-    private let lock = NSLock()
+public class Atomic<T> {
+    private var value: T
+    private let queue = DispatchQueue(label: "com.segment.atomic.\(UUID().uuidString)")
 
     public init(wrappedValue value: T) {
         self.value = value
     }
 
     public var wrappedValue: T {
-      get { return load() }
-      set { store(newValue: newValue) }
-    }
-
-    func load() -> T {
-        lock.lock()
-        defer { lock.unlock() }
-        return value
-    }
-
-    mutating func store(newValue: T) {
-        lock.lock()
-        defer { lock.unlock() }
-        value = newValue
+        get { return queue.sync { return value } }
+        set { queue.sync { value = newValue } }
     }
 }
diff --git a/Sources/Segment/Utilities/Policies/CountBasedFlushPolicy.swift b/Sources/Segment/Utilities/Policies/CountBasedFlushPolicy.swift
index a68abf07..2cadfa45 100644
--- a/Sources/Segment/Utilities/Policies/CountBasedFlushPolicy.swift
+++ b/Sources/Segment/Utilities/Policies/CountBasedFlushPolicy.swift
@@ -10,7 +10,7 @@ import Foundation
 public class CountBasedFlushPolicy: FlushPolicy {
     public weak var analytics: Analytics?
     internal var desiredCount: Int?
-    internal var count: Int = 0
+    @Atomic internal var count: Int = 0
     
     init() { }
     

From 1e74776098347e9b098078631f1f69795c6266d1 Mon Sep 17 00:00:00 2001
From: Brandon Sneed <brandon@redf.net>
Date: Tue, 27 Jun 2023 11:11:26 -0700
Subject: [PATCH 2/2] Additional reference

---
 Sources/Segment/Utilities/Atomic.swift | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Sources/Segment/Utilities/Atomic.swift b/Sources/Segment/Utilities/Atomic.swift
index fe39dff7..50984aba 100644
--- a/Sources/Segment/Utilities/Atomic.swift
+++ b/Sources/Segment/Utilities/Atomic.swift
@@ -14,6 +14,7 @@ import Foundation
 //
 // Additionally, moving to a lock free version is just desirable, so moved to a queue.
 //
+// Also see thread here: https://github.com/apple/swift-evolution/pull/1387
 
 @propertyWrapper
 public class Atomic<T> {