Function publish 

pub fn publish(
    device: &DeviceHandle,
    cache: &PipelineCache,
    dir: &Path,
) -> Result<bool, Error>

Replace the seed for device under dir with what cache holds, atomically, readable by every app and writable by its owner only. Ok(false) when the backend has no cache data to share.

Errors

When the directory or the file cannot be written.