I followed the readme instructions for building Parity from source and then executed:
cargo build --release
~/.cargo/bin/cargo build --release
as instructed, both of which returned the following message while the prompt hung:
Blocking waiting for file lock on the registry index
I'm on a Mac.
I suggest looking at 'Cargo build hangs with " Blocking waiting for file lock on the registry index" after building parity from source' first.
I had the same issue and had success with a quick and dirty
rm -rf ~/.cargo/registry/index/* ~/.cargo/.package-cache