Thread Sanitizer: Swift access race in Segment.CountBasedFlushPolicy.count.modify : Swift.Int at 0x11a75f4c0

[dmcgloin]

Describe the bug

When running our app with the Xcode Thread Sanitizer enabled, we sometimes see this runtime warning: Swift access race in Segment.CountBasedFlushPolicy.count.modify : Swift.Int at 0x11a75f4c0

It's flagged within the CountBasedFlushPolicy class at this line of code:

   public func updateState(event: RawEvent) {
        count += 1      <-----
    }

To Reproduce

1. Edit the current main app target (iOS) scheme
2. For the Run (Debug) section, select Diagnostics, enable "Thread Sanitizer" check box
3. Run app

Expected behavior
No runtime warnings

Platform (please complete the following information):

• Library Version in use: 1.4.5 (But I don't think this issue is new to this version)
• Platform being tested: iOS 16.4 on simulator
• Integrations in use: None except custom proxy

[dmcgloin]

FWIW, also just saw a new Thread Sanitizer warning with same release:

Swift access race in Segment.StartupQueue.running.getter : Swift.Bool at 0x11db41080

...at this code:

    public func execute<T: RawEvent>(event: T?) -> T? {
        if running == false, let e = event  {      <-----
            // timeline hasn't started, so queue it up.

[dannys42]

Also seen in reset():

    public func reset() {
        count = 0
    }

[bsneed]

Thanks guys! Just got back into the office today and will jump on this!

[bsneed]

FWIW, also just saw a new Thread Sanitizer warning with same release:

Swift access race in Segment.StartupQueue.running.getter : Swift.Bool at 0x11db41080

...at this code:

    public func execute<T: RawEvent>(event: T?) -> T? {
        if running == false, let e = event  {      <-----
            // timeline hasn't started, so queue it up.

Hmm, this one is interesting, as running is being hit via an accessor that uses nslock to acquire the value. I wonder if it's a false alarm.

[bsneed]

Fixed! Thanks for this everyone, I feel like it was a pretty significant improvement overall having looked at it with a TSan lens.

Another bug to fix, and then this will get released.

[bsneed]

Fixed in 1.4.6