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  • Note that neither process 2 nor process 3 will be able to signal EOF to the other while process 1 has the file descriptors open. Process 1 must close both descriptors so the write process will get a SIGPIPE signal if it writes to the pipe but the reader has terminated or closed the pipe. Similarly, the reader process will not be notified that the writer process has terminated or closed the pipe. That's because in each case, process 1 could write or read data because it has open file descriptors referring to the pipe file descriptors. Commented Oct 30, 2023 at 22:22
  • @JonathanLeffler: process 1 might wait for the end of process 2 and close the write end of the pipe immediately, even when process 3 is running (and vice versa). Gives the same effect as when process 1 just passes ownership of the file descriptors directly to proc 2 and 3 and lets them close the files directly. Commented Oct 30, 2023 at 22:32
  • And unless the sub-processes have a mechanism other than encountering EOF on read or failing to write, they will not terminate tidily. In particular, the writer might block waiting for a process to read data from the pipe, but no process is trying to read the pipe. Similarly, the reader might be blocked trying to read from an empty pipe that no process is going to write to. Care is required! Commented Oct 30, 2023 at 22:38
  • @JonathanLeffler: sure, but what do you think does this say about who should close the files? Commented Oct 30, 2023 at 23:03
  • It says process 1 should close both ends of the pipe before waiting on either process 2 or process 3. Otherwise, it will most likely be waiting “forever”. Commented Oct 30, 2023 at 23:33