@synchronized(self) 加锁引起的Crash

一、最近米家App进入前台的时候上报上来一个Crash

{"app_name":"MiHome","timestamp":"2019-04-03 11:00:09.66 +0800","app_version":"4.15.101","slice_uuid":"d41578a2-af0f-3fc5-b202-c120aeaacba2","adam_id":0,"build_version":"4.15.101.1334","bundleID":"com.xiaomi.mihome.dailybuild","share_with_app_devs":false,"is_first_party":false,"bug_type":"109","os_version":"iPhone OS 12.1 (16B92)","incident_id":"0DD1416C-EFFC-45CC-A5B1-7099FD5582E1","name":"MiHome"}
Incident Identifier: 0DD1416C-EFFC-45CC-A5B1-7099FD5582E1
CrashReporter Key:   0d34987d160e2a213f0eea4224c7be37b0e5f7ff
Hardware Model:      iPhone10,2
Process:             MiHome [12041]
Path:                /private/var/containers/Bundle/Application/C164FC42-7011-4900-B31D-C1FBF97A4927/MiHome.app/MiHome
Identifier:          com.xiaomi.mihome.dailybuild
Version:             4.15.101.1334 (4.15.101)
AppStoreTools:       10B61
Code Type:           ARM-64 (Native)
Role:                Non UI
Parent Process:      launchd [1]
Coalition:           com.xiaomi.mihome.dailybuild [15486]

Date/Time:           2019-04-03 11:00:09.4286 +0800
Launch Time:         2019-04-03 10:56:55.4746 +0800
OS Version:          iPhone OS 12.1 (16B92)
Baseband Version:    3.11.00
Report Version:      104

Exception Type:  EXC_CRASH (SIGKILL)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Exception Note:  EXC_CORPSE_NOTIFY
Termination Reason: Namespace SPRINGBOARD, Code 0x8badf00d
Termination Description: SPRINGBOARD, scene-update watchdog transgression: com.xiaomi.mihome.dailybuild exhausted real (wall clock) time allowance of 10.00 seconds | ProcessVisibility: Foreground | ProcessState: Running | WatchdogEvent: scene-update | WatchdogVisibility: Foreground | WatchdogCPUStatistics: ( | "Elapsed total CPU time (seconds): 3.890 (user 3.890, system 0.000), 6% CPU", | "Elapsed application CPU time (seconds): 0.695, 1% CPU" | )
Triggered by Thread:  0

Thread 0 name:  Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0   libsystem_kernel.dylib        	0x00000001c97a79fc __ulock_wait + 8
1   libsystem_platform.dylib      	0x00000001c981b8f8 _os_unfair_lock_lock_slow + 172
2   libobjc.A.dylib               	0x00000001c8df4830 objc_sync_enter + 32
3   MiHome                        	0x00000001035add48 -[MHTutkIotcManager registerNotifDictString] + 22076744 (MHTutkIotcManager.m:286)
4   MiHome                        	0x00000001035ad654 -[MHTutkIotcManager appEnterForeground:] + 22074964 (MHTutkIotcManager.m:241)
5   MiHome                        	0x0000000104b22c8c __43-[MHNotificationCenter processNotificaton:]_block_invoke + 44575884 (MHNotificationCenter.m:162)
6   CoreFoundation                	0x00000001c9af56bc -[__NSArrayM enumerateObjectsWithOptions:usingBlock:] + 216
7   MiHome                        	0x0000000104b22b6c -[MHNotificationCenter processNotificaton:] + 44575596 (MHNotificationCenter.m:164)
8   CoreFoundation                	0x00000001c9b7e928 __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20
9   CoreFoundation                	0x00000001c9b7e8f4 ___CFXRegistrationPost_block_invoke + 64
10  CoreFoundation                	0x00000001c9b7dde4 _CFXRegistrationPost + 392
11  CoreFoundation                	0x00000001c9b7da90 ___CFXNotificationPost_block_invoke + 96
12  CoreFoundation                	0x00000001c9af5d70 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1404
13  CoreFoundation                	0x00000001c9b7d51c _CFXNotificationPost + 696
14  Foundation                    	0x00000001ca58dc10 -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
15  UIKitCore                     	0x00000001f6e29c30 -[UIApplication _sendWillEnterForegroundCallbacks] + 232
16  UIKitCore                     	0x00000001f66abdc4 -[__UICanvasLifecycleMonitor_Compatability activateEventsOnly:withContext:completion:] + 2180
17  UIKitCore                     	0x00000001f66a9a74 __82-[_UIApplicationCanvas _transitionLifecycleStateWithTransitionContext:completion:]_block_invoke + 772
18  UIKitCore                     	0x00000001f66a9720 -[_UIApplicationCanvas _transitionLifecycleStateWithTransitionContext:completion:] + 432
19  UIKitCore                     	0x00000001f66ae8e0 __125-[_UICanvasLifecycleSettingsDiffAction performActionsForCanvas:withUpdatedScene:settingsDiff:fromSettings:transitionContext:]_block_invoke + 220
20  UIKitCore                     	0x00000001f66af840 _performActionsWithDelayForTransitionContext + 112
21  UIKitCore                     	0x00000001f66ae798 -[_UICanvasLifecycleSettingsDiffAction performActionsForCanvas:withUpdatedScene:settingsDiff:fromSettings:transitionContext:] + 248
22  UIKitCore                     	0x00000001f66b3684 -[_UICanvas scene:didUpdateWithDiff:transitionContext:completion:] + 368
23  UIKitCore                     	0x00000001f69f7090 -[UIApplicationSceneClientAgent scene:handleEvent:withCompletion:] + 468
24  FrontBoardServices            	0x00000001cc6456e4 __80-[FBSSceneImpl updater:didUpdateSettings:withDiff:transitionContext:completion:]_block_invoke.359 + 228
25  libdispatch.dylib             	0x00000001c964a484 _dispatch_client_callout + 16
26  libdispatch.dylib             	0x00000001c96213f0 _dispatch_block_invoke_direct$VARIANT$armv81 + 216
27  FrontBoardServices            	0x00000001cc683a9c __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 40
28  FrontBoardServices            	0x00000001cc683728 -[FBSSerialQueue _performNext] + 416
29  FrontBoardServices            	0x00000001cc683d44 -[FBSSerialQueue _performNextFromRunLoopSource] + 56
30  CoreFoundation                	0x00000001c9ba01cc __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 24
31  CoreFoundation                	0x00000001c9ba014c __CFRunLoopDoSource0 + 88
32  CoreFoundation                	0x00000001c9b9fa30 __CFRunLoopDoSources0 + 176
33  CoreFoundation                	0x00000001c9b9a8fc __CFRunLoopRun + 1040
34  CoreFoundation                	0x00000001c9b9a1cc CFRunLoopRunSpecific + 436
35  GraphicsServices              	0x00000001cbe11584 GSEventRunModal + 100
36  UIKitCore                     	0x00000001f6e11054 UIApplicationMain + 212
37  MiHome                        	0x00000001026e9a00 main + 6593024 (main.m:19)
38  libdyld.dylib                 	0x00000001c965abb4 start + 4

Thread 28 name:  Dispatch queue: com.apple.root.default-qos
Thread 28:
0   libsystem_kernel.dylib        	0x00000001c97a7428 __semwait_signal + 8
1   libsystem_c.dylib             	0x00000001c971c5d0 nanosleep + 212
2   libsystem_c.dylib             	0x00000001c971c4a4 usleep + 64
3   MiHome                        	0x00000001027a1d50 IOTC_Connect_UDP + 7347536 (UDP_Connect.c:2410)
4   MiHome                        	0x00000001035ac59c -[MHTutkIotcManager mh_iotcConnectByUIDParallel:uId:sId:] + 22070684 (MHTutkIotcManager.m:129)
5   MiHome                        	0x00000001035b28d0 __63-[MHTUTKP2PConnection connectIOTCDeviceWithUId:did:completion:]_block_invoke + 22096080 (MHTUTKP2PConnection.m:533)
6   libdispatch.dylib             	0x00000001c96496c8 _dispatch_call_block_and_release + 24
7   libdispatch.dylib             	0x00000001c964a484 _dispatch_client_callout + 16
8   libdispatch.dylib             	0x00000001c9620a7c _dispatch_queue_override_invoke + 664
9   libdispatch.dylib             	0x00000001c962cafc _dispatch_root_queue_drain + 344
10  libdispatch.dylib             	0x00000001c962d35c _dispatch_worker_thread2 + 116
11  libsystem_pthread.dylib       	0x00000001c982c17c _pthread_wqthread + 472
12  libsystem_pthread.dylib       	0x00000001c982ecec start_wqthread + 4

从Crash类型可以查询出来，Termination Reason: Namespace SPRINGBOARD, Code 0x8badf00d 代表主线程无响应，被watchdog杀掉了

主线程被阻塞，无非几种原因、死锁，方法执行耗时过长。

查询主线程，确实发现@synchronized(self) 加锁了，并且也是等锁导致等时间过长。子线程等方法中 使用了@synchronized加锁，内部操作长时间不返回，导致主线程被阻塞。

总结：

所有关于加锁的，一定要考虑加锁的粒度，同时考虑等锁等是不是主线程。

耗时过长的操作，设计线程安全的，可以放在队列中，使用队列解决。