parallel processing hangs forever after all processes finish when redirecting its output-CodePudding

With the following script:

#!/bin/bash

xerr() {
  sed -ue "s/^/(stderr) ${FUNCNAME[1]}: /" >&2
}
xlog() {
  sed -ue "s/^/(stdout) ${FUNCNAME[1]}: /"
}

main() {
  {
      sleep 0.25 && echo "ok" &
      sleep 1.00 && echo "ok" &
      sleep 0.65 && echo "fail" >&2 &
      sleep 1.00 && echo "ok" &
      sleep 0.65 && echo "ok" &
      wait
      echo "Finished"
  } 2> >(xerr) > >(xlog)
}

main

Background processes finish successfully, but hang forever in wait:

(stdout) main: ok
(stdout) main: ok
(stderr) main: fail
(stdout) main: ok
(stdout) main: ok
^C

However when (1) not redirecting its output or (2) not running in parallel, all is working as expected:

#(1)
main() {
  {
      sleep 0.25 && echo "ok"
      sleep 1.00 && echo "ok"
      sleep 0.65 && echo "fail" >&2
      sleep 1.00 && echo "ok"
      sleep 0.65 && echo "ok"
      echo "Finished"
  } 2> >(xerr) > >(xlog)
}

main

#(stdout) main: ok
#(stdout) main: ok
#(stderr) main: fail
#(stdout) main: ok
#(stdout) main: ok
#(stdout) main: Finished

#(2)
main() {
  {
      sleep 0.25 && echo "ok" &
      sleep 1.00 && echo "ok" &
      sleep 0.65 && echo "fail" >&2 &
      sleep 1.00 && echo "ok" &
      sleep 0.65 && echo "ok" &
      wait
      echo "Finished"
  }
}

main

# ok
# fail
# ok
# ok
# ok
# Finished

Is there any reason for this? How can I run processes in parallel and redirect their output at the same time?

CodePudding user response：

Is there any reason for this?

>(xerr) and >(xlog) are also background processes; wait is waiting for (at least one of) them too.

How can I run processes in parallel and redirect their output at the same time?

main() {
  { { {
    sleep 0.25 && echo "ok" &
    sleep 1.00 && echo "ok" &
    sleep 0.65 && echo "fail" >&2 &
    sleep 1.00 && echo "ok" &
    sleep 0.65 && echo "ok" &
    wait
    echo "Finished"
  } 2>&4 | xlog >&3; } 4>&1 | xerr >&3; } 3>&1
}