Cargo Features

workerpool has no features set by default.

[dependencies]
workerpool = { version = "1.2.1", features = ["crossbeam"] }
crossbeam = crossbeam-channel

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

crossbeam-channel crossbeam?