A pair of channels that implements a unidirectional pipe.
A pipe consists of a pair of channels: A writable sink channel and a readable source
channel. Once some bytes are written to the sink channel they can be read
from source channel in exactlyAthe order in which they were written.
Whether or not a thread writing bytes to a pipe will block until another thread reads those bytes, or some previously-written bytes, from the pipe is system-dependent and therefore unspecified. Many pipe implementations will buffer up to a certain number of bytes between the sink and source channels, but such buffering should not be assumed.