10. Thread Sanitizer & Runtime Detection

Meskipun Swift 6 mendeteksi data race di compile time, Thread Sanitizer (TSan) tetap berguna untuk:

Mendeteksi race di kode @unchecked Sendable
Mendeteksi race yang melalui C/ObjC boundary
Validasi kode concurrent selama migration ke Swift 6

Mengaktifkan TSan

swift
# Via command line
swift test --sanitize=thread

# Di Xcode: Product > Scheme > Edit Scheme > Run > Diagnostics > Thread Sanitizer

Membaca TSan Report

swift
WARNING: ThreadSanitizer: data race (pid=12345)
  Write of size 8 at 0x... by thread T2:
    #0 UserCache.store(user:forKey:) UserCache.swift:15
    #1 ...
    
  Previous read of size 8 at 0x... by main thread:
    #0 UserCache.user(forKey:) UserCache.swift:19
    #1 ...
    
SUMMARY: ThreadSanitizer: data race UserCache.swift:15

Interpretasi:

Thread T2 melakukan write ke alamat memori tertentu di baris 15
Main thread melakukan read dari alamat yang sama di baris 19
Keduanya terjadi tanpa synchronization → data race

TSan Suppression untuk False Positives

swift
// Jika TSan melaporkan false positive untuk @unchecked Sendable
// yang sudah benar-benar thread-safe

// File: tsan_suppressions.txt
// race:ThreadSafeQueue::enqueue
// race:ThreadSafeQueue::dequeue

// Aktifkan suppression file
// TSAN_OPTIONS="suppressions=tsan_suppressions.txt" swift test --sanitize=thread