isIsolatingCurrentContext()

Declaration

func isIsolatingCurrentContext() -> Bool?

Discussion

This function can be called by the runtime in order to perform assertions, or attempt to issue warnings about unexpected isolation.

This method will be invoked before checkIsolated and may also be invoked when crashing is not an acceptable outcome of a check (e.g. when attempting to issue isolation warnings).

Implementations should prefer to implement this method rather than checkIsolated() since it can often result in more tailored error messages. It is allowed, and useful for backwards compatibility with old runtimes which are not able to invoke isIsolatingCurrentContext() to implement checkIsolated(), even if an implementation is able to implement this method. Often times an implementation of checkIsolated(), would then invoke isIsolatingCurrentContext() and crash if the returned value was false.

The default implementation returns nil is used to indicate that it is “unknown” if the current context is isolated by this serial executor. The runtime then may proceed to invoke checkIsolated() as a last-resort attempt to verify the isolation of the current context.