Thread 3:
0 libsystem_kernel.dylib 0x00000001e2cafaf8 __ulock_wait2 + 8
1 libsystem_platform.dylib 0x000000021c0f8630 os_unfair_lock_lock_slow + 176 (lock.c:608)
2 libobjc.A.dylib 0x000000018f020f3c objc_readClassPair + 84 (objc-runtime-new.mm:9085)
3 libswiftCore.dylib 0x00000001904f1c64 swift_initClassMetadataImpl(swift::TargetClassMetadata<swift::InProcess, swift::TargetAnyClassMetadataObjCInteropswift::InProcess>, swift::ClassLayoutFlags, unsigned long, swift::TargetTypeLayo... + 4412 (Metadata.cpp:4312)
4 libswiftCore.dylib 0x0000000190493af0 type metadata completion function for _KeyedEncodingContainerBox + 112 (:0)
5 libswiftCore.dylib 0x00000001904fe7a4 swift::MetadataCacheEntryBase<(anonymous namespace)::GenericCacheEntry, void const>::doInitialization(swift::MetadataWaitQueue::Worker&, swift::MetadataRequest) + 860 (MetadataCache.h:1300)
6 libswiftCore.dylib 0x00000001904eb668 swift_getGenericMetadata(swift::MetadataRequest, void const* const*, swift::TargetTypeContextDescriptorswift::InProcess const*) + 2336 (Metadata.cpp:982)
7 libswiftCore.dylib 0x00000001904b6564 __swift_instantiateGenericMetadata + 36 (:0)
8 libswiftCore.dylib 0x000000019018d2a0 KeyedEncodingContainer.init(:) + 48 (Codable.swift:547)
9 Foundation 0x000000019082cf08 __PlistEncoderBPlist.container(keyedBy:) + 344 (BPlistEncodingFormat.swift:94)
10 Foundation 0x000000019082cf4c protocol witness for Encoder.container(keyedBy:) in conformance __PlistEncoderBPlist + 24 (:0)
11 Tiercel 0x0000000106ff22c0 DownloadTask.encode(to:) + 176 (DownloadTask.swift:120)
12 Tiercel 0x000000010701e8c8 protocol witness for Encodable.encode(to:) in conformance Task + 44 (/:0)
13 libswiftCore.dylib 0x0000000190490b8c dispatch thunk of Encodable.encode(to:) + 32
14 Foundation 0x0000000190832af0 specialized closure #1 in __PlistEncoderBPlist.wrapGeneric<A, B>(:for::) + 144 (BPlistEncodingFormat.swift:500)
15 Foundation 0x0000000190832b30 partial apply for specialized closure #1 in __PlistEncoderBPlist.wrapGeneric<A, B>(:for::) + 24 (:0)
16 Foundation 0x000000019082c84c specialized __PlistEncoderBPlist.wrapGeneric(:for::) + 368 (BPlistEncodingFormat.swift:515)
17 Foundation 0x0000000190832a2c specialized __PlistEncoderBPlist.wrapGeneric<A, B>(:for::) + 836 (BPlistEncodingFormat.swift:499)
18 Foundation 0x000000019086ecc4 PlistUnkeyedEncodingContainerBPlist.encode(:) + 292 (BPlistEncodingFormat.swift:354)
19 Foundation 0x000000019086eb98 protocol witness for UnkeyedEncodingContainer.encode(:) in conformance PlistUnkeyedEncodingContainerBPlist + 16 (:0)
20 libswiftCore.dylib 0x00000001901b0e60 Array.encode(to:) + 440 (Codable.swift:6032)
21 libswiftCore.dylib 0x00000001901b0fa0 protocol witness for Encodable.encode(to:) in conformance [A] + 32 (:0)
22 libswiftCore.dylib 0x0000000190490b8c dispatch thunk of Encodable.encode(to:) + 32
23 Foundation 0x0000000190832af0 specialized closure #1 in __PlistEncoderBPlist.wrapGeneric<A, B>(:for::) + 144 (BPlistEncodingFormat.swift:500)
24 Foundation 0x0000000190832b30 partial apply for specialized closure #1 in __PlistEncoderBPlist.wrapGeneric<A, B>(:for::) + 24 (:0)
25 Foundation 0x000000019082c84c specialized __PlistEncoderBPlist.wrapGeneric(:for::) + 368 (BPlistEncodingFormat.swift:515)
26 Foundation 0x0000000190832a2c specialized __PlistEncoderBPlist.wrapGeneric<A, B>(:for::) + 836 (BPlistEncodingFormat.swift:499)
27 Foundation 0x0000000190832558 PropertyListEncoder.encodeToTopLevelContainerBPlist(:) + 188 (PlistEncoder.swift:216)
28 Foundation 0x0000000190831f54 PropertyListEncoder.encodeBPlist(:) + 44 (PlistEncoder.swift:120)
29 Foundation 0x00000001908318c4 PropertyListEncoder.encode(:) + 140 (PlistEncoder.swift:103)
30 Foundation 0x0000000190831684 dispatch thunk of PropertyListEncoder.encode(:) + 48
31 Tiercel 0x0000000106feb830 closure #1 in Cache.storeTasks(:) + 360 (Cache.swift:259)
32 Tiercel 0x0000000106fea818 thunk for @escaping @callee_guaranteed () -> () + 28 (/:0)
33 Tiercel 0x0000000107000d18 closure #1 in closure #1 in Debouncer.execute(label:time:execute:) + 44 (Protected.swift:127)
34 Tiercel 0x0000000106fea818 thunk for @escaping @callee_guaranteed () -> () + 28 (/:0)
35 libdispatch.dylib 0x0000000199a2c2b8 _dispatch_block_async_invoke2 + 148 (queue.c:574)
36 libdispatch.dylib 0x0000000199a36584 _dispatch_client_callout + 16 (client_callout.mm:85)
37 libdispatch.dylib 0x0000000199a21560 _dispatch_continuation_pop + 596 (queue.c:325)
38 libdispatch.dylib 0x0000000199a34348 _dispatch_source_latch_and_call + 396 (source.c:601)
39 libdispatch.dylib 0x0000000199a33020 _dispatch_source_invoke + 844 (source.c:966)
40 libdispatch.dylib 0x0000000199a25138 _dispatch_lane_serial_drain + 332 (queue.c:3939)
41 libdispatch.dylib 0x0000000199a25de0 _dispatch_lane_invoke + 440 (queue.c:4030)
42 libdispatch.dylib 0x0000000199a301dc _dispatch_root_queue_drain_deferred_wlh + 292 (queue.c:7198)
43 libdispatch.dylib 0x0000000199a2fa60 _dispatch_workloop_worker_thread + 540 (queue.c:6792)
44 libsystem_pthread.dylib 0x000000021c1a0a0c _pthread_wqthread + 292 (pthread.c:2696)
45 libsystem_pthread.dylib 0x000000021c1a0aac start_wqthread + 8

在 Cache 的 storeTasks 方法中，在 io 线程中对 tasks 进行存储时，需要 encode tasks，由于 encode 获取 encode 对象元数据不是线程安全的，有几率产生死锁，不能在全局线程中 encode 对象。