Prefetch units corresponding to the given sets of paths, before they are actually needed
namespace HH; function prefetch_units( keyset<string> $paths, bool $hint, ): void;
If $hint is true, this request is non-binding. That is, the runtime may attempt to asynchronously prefetch the units in the background, or maybe not do anything at all. The units may not (and probably won't be) loaded when this function returns.
If $hint is false, the runtime will always attempt to prefetch the units and will block until they have been. Therefore when this function returns, the units have been loaded. Note: depending on configuration, this may be slower than a non-binding request.