Thread Sanitizer detects race condition in AFRKURLConnectionOperation state getter

[pieceofsummer]

When running a project built with Thread Sanitizer enabled, the following data race is detected sometimes:

==================
WARNING: ThreadSanitizer: data race (pid=33711)
  Read of size 2 at 0x7b3c00085f3c by thread T25:
  * #0 -[AFRKURLConnectionOperation state] AFRKURLConnectionOperation.m:133 (project:x86_64+0x10011c51c)
    #1 -[AFRKURLConnectionOperation isFinished] AFRKURLConnectionOperation.m:499 (project:x86_64+0x100114326)
    #2 __NSOQSchedule_f <null>:8182160 (Foundation:x86_64+0x3c632)
    #3 _dispatch_client_callout <null>:8182160 (libdispatch.dylib:x86_64+0x2b05b)

  Previous write of size 2 at 0x7b3c00085f3c by thread T11 (mutexes: write M660194180576176032):
  * #0 -[AFRKURLConnectionOperation setState:] AFRKURLConnectionOperation.m:417 (project:x86_64+0x10011290c)
    #1 -[AFRKURLConnectionOperation finish] AFRKURLConnectionOperation.m:547 (project:x86_64+0x10011578e)
    #2 -[AFRKURLConnectionOperation connectionDidFinishLoading:] AFRKURLConnectionOperation.m:772 (project:x86_64+0x10011aa0b)
    #3 __65-[NSURLConnectionInternal _withConnectionAndDelegate:onlyActive:]_block_invoke <null>:8182160 (CFNetwork:x86_64+0x29268)
    #4 __NSThread__start__ <null>:8182160 (Foundation:x86_64+0x31130)

  Issue is caused by frames marked with "*".

  Location is heap block of size 240 at 0x7b3c00085f20 allocated by main thread:
    #0 calloc <null>:8182176 (libclang_rt.tsan_iossim_dynamic.dylib:x86_64+0x46be2)
    #1 class_createInstance <null>:8182176 (libobjc.A.dylib:x86_64+0xfba0)
    #2 -[UIImageView(AFRKNetworking) setImageWithURL:placeholderImage:] UIImageView+AFRKNetworking.m:92 (project:x86_64+0x10026300c)
    #3 -[ShowDetailsController tableView:cellForRowAtIndexPath:] ShowDetailsController.m:130 (project:x86_64+0x10004cfd7)
    #4 -[UITableView _createPreparedCellForGlobalRow:withIndexPath:willDisplay:] <null>:8182176 (UIKit:x86_64+0x194ab1)
    #5 start <null>:8182176 (libdyld.dylib:x86_64+0x465c)

  Mutex M660194180576176032 is already destroyed.

  Thread T25 (tid=1351743, running) is a GCD worker thread

  Thread T11 (tid=1347018, running) created by thread T2 at:
    #0 pthread_create <null>:8182240 (libclang_rt.tsan_iossim_dynamic.dylib:x86_64+0x28f4d)
    #1 -[NSThread start] <null>:8182240 (Foundation:x86_64+0x30c4c)
    #2 dispatch_once <null>:8182240 (libclang_rt.tsan_iossim_dynamic.dylib:x86_64+0x64464)
    #3 +[AFRKURLConnectionOperation networkRequestThread] once.h:84 (project:x86_64+0x10010dcf4)
    #4 -[AFRKURLConnectionOperation start] AFRKURLConnectionOperation.m:511 (project:x86_64+0x100114554)
    #5 -[RKObjectRequestOperation execute] RKObjectRequestOperation.m:521 (project:x86_64+0x100213454)
    #6 __77-[RKObjectRequestOperation initWithHTTPRequestOperation:responseDescriptors:]_block_invoke RKObjectRequestOperation.m:330 (project:x86_64+0x10020f8e1)
    #7 __45-[RKOperationStateMachine setExecutionBlock:]_block_invoke_2 RKOperationStateMachine.m:175 (project:x86_64+0x10021e8f7)
    #8 __tsan::invoke_and_release_block(void*) <null>:8182240 (libclang_rt.tsan_iossim_dynamic.dylib:x86_64+0x637fb)
    #9 _dispatch_client_callout <null>:8182240 (libdispatch.dylib:x86_64+0x2b05b)

SUMMARY: ThreadSanitizer: data race AFRKURLConnectionOperation.m:133 in -[AFRKURLConnectionOperation state]
==================

Adding an explicit state getter (with lock guard) seems to fix the issue:

- (AFRKOperationState)state {
    AFRKOperationState state;
    [self.lock lock];
    state = _state;
    [self.lock unlock];
    return state;
}