This is because the caching code assumes that flock can be used to atomically switch between lock modes. However, this isn't the case. Another process may have come along and extracted the image already while we were waiting to acquire the exclusive lock.
Testing many packages concurrently can create the following error:
This is because the caching code assumes that flock can be used to atomically switch between lock modes. However, this isn't the case. Another process may have come along and extracted the image already while we were waiting to acquire the exclusive lock.