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Hi,I get a data race error for a singleton.It is implemented exactly as described in the WWDC session about thread sanitizer as the "correct implementation":How can I fix it? + (SomeSingleton *)sharedSessionContext { static SomeSingleton *sharedInstance = nil; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ sharedInstance = [[SomeSingleton alloc] initSingleton]; }); return sharedInstance; }The Thread sanitizer emits:WARNING: ThreadSanitizer: data race (pid=16374) Write of size 8 at 0x0001105d9818 by thread T13: #0 +[SomeSingleton sharedSessionContext] <null> (MyApp:x86_64+0x10226e826) #1 -[SomeView loadLogoLoggedIn] <null> (MyApp:x86_64+0x10098e863) #2 -[SomeView loadData] <null> (MyApp:x86_64+0x100989b6a) #3 __NSThread__start__ <null> (Foundation:x86_64+0xc024a) Previous write of size 8 at 0x0001105d9818 by thread T6: #0 +[SomeSingleton sharedSessionContext] <null> (MyApp:x86_64+0x10226e826) [...] #7 __116-[AFHTTPSessionManager dataTaskWithHTTPMethod:URLString:parameters:uploadProgress:downloadProgress:success:failure:]_block_invoke_2 <null> (AFNetworking:x86_64+0xb14d) #8 __72-[AFURLSessionManagerTaskDelegate URLSession:task:didCompleteWithError:]_block_invoke_2.123 <null> (AFNetworking:x86_64+0x4c7e1) #9 __wrap_dispatch_group_async_block_invoke <null> (libclang_rt.tsan_iossim_dynamic.dylib:x86_64+0x6b627) #10 _dispatch_client_callout <null> (libdispatch.dylib:x86_64+0x3db4) Location is global '__llvm_gcov_ctr.2343' at 0x0001105d9818 (MyApp+0x000107c8c818) Thread T13 (tid=252686, running) created by main thread at: #0 pthread_create <null> (libclang_rt.tsan_iossim_dynamic.dylib:x86_64+0x2912d) #1 -[NSThread start] <null> (Foundation:x86_64+0xbfd66) [...] #7 -[MyViewController viewWillAppear:] <null> (Base:x86_64+0x1a658e) #8 -[UIViewController _setViewAppearState:isAnimating:] <null> (UIKitCore:x86_64+0x3530f2) #9 start <null> (libdyld.dylib:x86_64+0x1540) Thread T6 (tid=252621, running) is a GCD worker thread SUMMARY: ThreadSanitizer: data race ... in +[SomeSingleton sharedSessionContext]