Merge pull request #27808 from apple/tsan-empty-array-storage

[TSan] Do not report benign race on `_swiftEmptyArrayStorage`

Author: yln

stdlib/public/core/Array.swift

@@ -1162,7 +1162,7 @@ extension Array: RangeReplaceableCollection {
       "newElements.underestimatedCount was an overestimate")
     // can't check for overflow as sequences can underestimate
 
-    // This check prevents a data race writting to _swiftEmptyArrayStorage
+    // This check prevents a data race writing to _swiftEmptyArrayStorage
     if writtenCount > 0 {
       _buffer.count += writtenCount
     }

stdlib/public/core/ArraySlice.swift

@@ -953,7 +953,10 @@ extension ArraySlice: RangeReplaceableCollection {
       "newElements.underestimatedCount was an overestimate")
     // can't check for overflow as sequences can underestimate
 
-    _buffer.count += writtenCount
+    // This check prevents a data race writing to _swiftEmptyArrayStorage
+    if writtenCount > 0 {
+      _buffer.count += writtenCount
+    }
 
     if writtenUpTo == buf.endIndex {
       // there may be elements that didn't fit in the existing buffer,

stdlib/public/core/ContiguousArray.swift

@@ -801,7 +801,10 @@ extension ContiguousArray: RangeReplaceableCollection {
       "newElements.underestimatedCount was an overestimate")
     // can't check for overflow as sequences can underestimate
 
-    _buffer.count += writtenCount
+    // This check prevents a data race writing to _swiftEmptyArrayStorage
+    if writtenCount > 0 {
+      _buffer.count += writtenCount
+    }
 
     if writtenUpTo == buf.endIndex {
       // there may be elements that didn't fit in the existing buffer,

stdlib/public/core/ContiguousArrayBuffer.swift

@@ -688,7 +688,7 @@ internal struct _UnsafePartiallyInitializedContiguousArrayBuffer<Element> {
       p = newResult.firstElementAddress + result.capacity
       remainingCapacity = newResult.capacity - result.capacity
       if !result.isEmpty {
-        // This check prevents a data race writting to _swiftEmptyArrayStorage
+        // This check prevents a data race writing to _swiftEmptyArrayStorage
         // Since count is always 0 there, this code does nothing anyway
         newResult.firstElementAddress.moveInitialize(
           from: result.firstElementAddress, count: result.capacity)

test/Sanitizers/tsan-emptyarraystorage.swift

@@ -1,6 +1,6 @@
 // RUN: %target-swiftc_driver %s -target %sanitizers-target-triple -g -sanitize=thread -o %t_tsan-binary
 // RUN: %target-codesign %t_tsan-binary
-// RUN: %target-run %t_tsan-binary 2>&1 | %FileCheck %s
+// RUN: %target-run %t_tsan-binary 2>&1 | %FileCheck %s --implicit-check-not='ThreadSanitizer'
 // REQUIRES: executable_test
 // REQUIRES: tsan_runtime
 // REQUIRES: foundation
@@ -14,28 +14,47 @@ import Foundation
 
 let sem = DispatchSemaphore(value: 0)
 
-class T1: Thread {
+class T: Thread {
+  let closure: () -> Void
+  init(closure: @escaping () -> Void) {
+    self.closure = closure
+  }
   override func main() {
-    var oneEmptyArray: [[String:String]] = []
-    oneEmptyArray.append(contentsOf: [])
+    closure()
     sem.signal()
   }
 }
-let t1 = T1()
-t1.start()
 
-class T2: Thread {
-  override func main() {
-    var aCompletelyUnrelatedOtherEmptyArray: [[Double:Double]] = []
-    aCompletelyUnrelatedOtherEmptyArray.append(contentsOf: [])
-    sem.signal()
-  }
+func runOnThread(_ closure: @escaping () -> Void) {
+  let t = T(closure: closure)
+  t.start()
+}
+
+runOnThread {
+  var oneEmptyArray: [[String:String]] = []
+  oneEmptyArray.append(contentsOf: [])
+}
+runOnThread {
+  var aCompletelyUnrelatedOtherEmptyArray: [[Double:Double]] = []
+  aCompletelyUnrelatedOtherEmptyArray.append(contentsOf: [])
+}
+runOnThread {
+  var array = Array<Int>()
+  array.append(contentsOf: [])
+}
+runOnThread {
+  var arraySlice = ArraySlice<Int>()
+  arraySlice.append(contentsOf: [])
+}
+runOnThread {
+  var contiguousArray = ContiguousArray<Int>()
+  contiguousArray.append(contentsOf: [])
+}
+
+for _ in 1...5 {
+  sem.wait()
 }
-let t2 = T2()
-t2.start()
 
-sem.wait()
-sem.wait()
 print("Done!")
 
 // CHECK: Done!