POSIX port doesn't copy small files about dd-parallel

[boredzo]

Debug logging:

Reading into buffer 0
Finished reading into buffer 0
Waiting to read into buffer 1…
Reader generation check: Read gen 0, write gen 0
Reading into buffer 1
Finished reading buffer 1. This is read generation 1, chunk #
Read loop reached end of input file
Read loop exiting
Waiting to write buffer 1 (reader state is 2)…
Writer generation check: Read gen 1, write gen 0
Writing buffer 1, which is chunk #
Finished writing buffer 1. This is write generation 0, chunk #
Write loop exiting because readerState is 4
Copied 0 bytes in 0 ms (overall avg 0 bytes/sec)

[boredzo]

Added the read amounts to the log. As expected, the initial read is the length of the file and the second read is 0:

Reading into buffer 0
Finished reading 1546 bytes into buffer 0
Waiting to read into buffer 1…
Reader generation check: Read gen 0, write gen 0
Reading into buffer 1
Finished reading 0 bytes into buffer 1. This is read generation 1, chunk #
Read loop reached end of input file
Read loop exiting
Write loop exiting because readerState is 4
Copied 0 bytes in 0 ms (overall avg 0 bytes/sec)

[boredzo]

Seems like the writer thread needs to be controlled not by the reader's state, but on the generation counts. In fact, it seems like this could happen at the end of a long file, not just on a small one.