When creating a PipedInputStream and PipedOutputStream like the following:

PipedOutputStream out = new PipedOutputStream();
PipedInputStream in = new PipedInputStream(out) ...

PipedOutputStream#connect will be called by the thread with the PipedInputStream and write to the field PipedOutputStream.sink, and that field will be read in the other thread by methods like PipedOutputStream#write.

PipedOutputStream#connect is synchronized so the write is guarded by a lock, but PipedOutputStream#write is not synchronized, so the read is racy.