This blog post has some good discussion about what makes a good locking primitive. On macOS, os_unfair_lock is generally a good choice for many applications. That said,
> At this point, you might wonder if os_unfair_lock – possibly coupled with the undocumented flags – would be a good fit for your codebase. My answer is likely yes but you’ll have to be careful when using it.
I would hesitate to give this advice. The overwhelming majority of applications on macOS do not have performance profiles like Firefox does. The system allocator (rather than jemalloc) is the right choice for all but very few use cases. There are a vanishingly small number of usecases where using the undocumented flags is appropriate.
The rules are different when you’re a popular browser with an existing relationship with Apple and dozens of smart engineers who can (at least in theory) understand the consequences of using this API, and leverage an existing relationship with Apple to ensure that it doesn’t become a liability in the future as the platform evolves. For pretty much everyone else, this should be nothing more than a “wow, neat” blog post.
> At this point, you might wonder if os_unfair_lock – possibly coupled with the undocumented flags – would be a good fit for your codebase. My answer is likely yes but you’ll have to be careful when using it.
I would hesitate to give this advice. The overwhelming majority of applications on macOS do not have performance profiles like Firefox does. The system allocator (rather than jemalloc) is the right choice for all but very few use cases. There are a vanishingly small number of usecases where using the undocumented flags is appropriate.
The rules are different when you’re a popular browser with an existing relationship with Apple and dozens of smart engineers who can (at least in theory) understand the consequences of using this API, and leverage an existing relationship with Apple to ensure that it doesn’t become a liability in the future as the platform evolves. For pretty much everyone else, this should be nothing more than a “wow, neat” blog post.