Hi everyone,
I don’t know if it’s the good place to ask for this, so if it’s not, please be kind enough to tell me where I should post this question.
I’m having a hard time figuring out why, since I activated ThreadSanitizer to my Xcode 9 scheme, I keep seeing race conditions when using OperationQueue and a custom BlockOperation subclass I made to deal with Asynchronous operations.
If I refer to the documentation on Operation, it says that isCancelled, isFinished, isExecuting properties must be thread safe since you never know from which thread they can be invoked. So I decided to go for a pthread_mutex_lock/unlock to protect the critical parts. For instance isFinished looks like this:
class AsyncBlockOperation : BlockOperation {
enum State: String {
case ready = "Ready",
executing = "Executing",
finished = "Finished"
fileprivate var keyPath: String {
return "is" + self.rawValue
}
}
private var state: State = .ready
{
willSet {
willChangeValue(forKey: state.keyPath)
willChangeValue(forKey: newValue.keyPath)
}
didSet {
didChangeValue(forKey: oldValue.keyPath)
didChangeValue(forKey: state.keyPath)
}
}
private var mutex = pthread_mutex_t()
override var isFinished: Bool {
pthread_mutex_lock(&mutex)
defer { pthread_mutex_unlock(&mutex) }
return state == .finished
}
/* Same goes for isCancelled, and isExecuting… */
}
I thought that the problem of « thread-safe » would be solved with these lock/unlock mutex but when an other thread accesses one of the these properties I get a data race warning by the ThreadSanitizer.
What do I do wrong?
Is it possible that ThreadSanitizer reports a false positive? How should I debug this kind of issue?
Any help would be much appreciated. I can provide a Xcode test project with a running example of this issue.
Thanks in advance.
Best regards,
Thierry