We have a decent amount of internal synchronization infrastructure for locking, notification, and threading. They live in these src directories:

• mongo/stdx
• mongo/platform
• mongo/util

There are three topics here:

• Locking and Latching (includes Mutex, WithLock, SpinLock, LatchAnalyzer, DiagnosticInfo)
• Notification (Notifyable, stdx::condition_variable, Notification)
• Threading (BackgroundJob, PeriodicRunner[Impl], stdx::thread)

Since this spans several directories, we should make a new markdown in the docs folder. This is intended to be abstract documentation, describe relationships and state transitions not code in common language.