error is accrue

[junhee0720]

error.
show command is

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
2017-08-01 19:17:29.219 ysmobile[619:63986] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSOperationInternal _start:]: receiver is already executing'
*** First throw call stack:
(0x18258edb0 0x181bf3f80 0x18258ecf8 0x182e8ac90 0x10123534c 0x101235624 0x101235678 0x101cb5a7c 0x101cb5a3c 0x101cbb4e4 0x182544d50 0x182542bb8 0x18246cc50 0x183d54088 0x187756088 0x10010e494 0x18200a8b8)
libc++abi.dylib: terminating with uncaught exception of type NSException

Xcode. Show Source is

  // MARK: Operation Subclassing
  override open func start() {
    guard Thread.isMainThread else {
      DispatchQueue.main.async { [weak self] in
        self?.start()
      }
      return
    }
    super.start() <- IDE error , Thread 1:signal SIGABRT
  }