Thread Sanitizer warnings

[Jesse Grosjean]

I get Swift access race in Squid.Locked.lock() -> () at 0x7b080002f4e0 when running Squid under Xcode thread sanitizer. My understanding is there's not currently an actual issue in the threading code due to the way that Swift is generating code, but the thread analyzer can't be sure, so generates the warning.

I think to fix warning you can replace:

internal class Locked<Value> {
    private var _lock = os_unfair_lock()
    ...

with:

internal class Locked<Value> {
    private var _lock: UnsafeMutablePointer<os_unfair_lock>

    init(_ value: Value) {
        _lock = UnsafeMutablePointer<os_unfair_lock>.allocate(capacity: 1)
        _lock.initialize(to: os_unfair_lock())
        self._value = value
    }

I found this solution and an explanation here:

http://www.russbishop.net/the-law