nc 和 fifo 的奇怪不一致输出

Question

我有这个确切的代码：

#!/bin/bash

gtimeout(){
  if type -f gtimeout &> /dev/null; then
    command gtimeout "$@"
  else
    timeout "$@"
  fi
}

export -f gtimeout;


on_first_match(){
   local pattern="$1"  # The pattern to search for
    while IFS= read -r line; do
        if [[ "$line" == *"$pattern"* ]]; then
            exit 0
        fi
    done
}

export -f on_first_match


write_to_server(){
  echo -e "$?" | nc 0.0.0.0 3333
}

export -f write_to_server

(

set +e;
sleep 2;

  (
     gtimeout 15 docker logs -f rabbitmq-node1 | on_first_match 'Starting listener on';
     write_to_server
  ) &


  (
    gtimeout 15 docker logs -f mongodb-node1 | on_first_match 'waiting for connections';
    write_to_server
  ) &


  (
    gtimeout 15 docker logs -f elasticsearch-node1 | on_first_match 'started';
    write_to_server
  ) &


  (
     gtimeout 15 docker logs -f rabbitmq-node2 | on_first_match 'Starting listener on';
     write_to_server
  ) &


  (
    gtimeout 15 docker logs -f mongodb-node2 | on_first_match 'waiting for connections';
    write_to_server
  ) &


  (
    gtimeout 15 docker logs -f elasticsearch-node2 | on_first_match 'started';
    write_to_server
  ) &


  (
     gtimeout 15 docker logs -f rabbitmq-node3 | on_first_match 'Starting listener on';
     write_to_server
  ) &


  (
    gtimeout 15 docker logs -f mongodb-node3 | on_first_match 'waiting for connections';
    write_to_server
  ) &


  (
    gtimeout 15 docker logs -f elasticsearch-node3 | on_first_match 'started';
    write_to_server
  ) &


) &

gtimeout 30 nc -k -l 3333 | while IFS= read -r line; do
      echo "Received: $line";
done

我得到的输出是这样的：

Error response from daemon: No such container: mongodb-node1
Error response from daemon: No such container: rabbitmq-node2
Error response from daemon: No such container: rabbitmq-node1
Error response from daemon: No such container: elasticsearch-node2
Error response from daemon: No such container: elasticsearch-node1
Error response from daemon: No such container: mongodb-node2
Error response from daemon: No such container: mongodb-node3
Error response from daemon: No such container: rabbitmq-node3
Error response from daemon: No such container: elasticsearch-node3
Received: 0
Received: 0
Received: 0
Received: 0
Received: 0

（仅收到 5 条线，有时 4 条，有时 6 条，但从来没有像预期的那样收到 9 条）

但我期望这样：

Error response from daemon: No such container: mongodb-node1
Error response from daemon: No such container: rabbitmq-node2
Error response from daemon: No such container: rabbitmq-node1
Error response from daemon: No such container: elasticsearch-node2
Error response from daemon: No such container: elasticsearch-node1
Error response from daemon: No such container: mongodb-node2
Error response from daemon: No such container: mongodb-node3
Error response from daemon: No such container: rabbitmq-node3
Error response from daemon: No such container: elasticsearch-node3
Received: 0
Received: 0
Received: 0
Received: 0
Received: 0
Received: 0
Received: 0
Received: 0
Received: 0

有 9 条接收线。

有人知道这是怎么回事吗？ （当我将代码切换为 mkfifo 而不是套接字时，会发生相同的行为）。