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在 bash 中运行多个异步任务并获取它们的输出和退出代码

tag-icon • tag-icon linux command-line bash unix job-control
在 bash 中运行多个异步任务并获取它们的输出和退出代码

我必须异步运行一堆命令，一旦其中一个命令完成，我就需要根据其退出代码和输出执行操作。请注意，我无法预测这些任务在我的实际用例中将运行多长时间。

为了解决这个问题，我最终得到了以下算法：

For each task to be run:
    Run the task asynchronously;
    Append the task to the list of running tasks.
End For.

While there still are tasks in the list of running tasks:
    For each task in the list of running tasks:
        If the task has ended:
            Retrieve the task's exit code and output;
            Remove the task from the list of running tasks.
        End If.
    End For
End While.

这给了我以下 bash 脚本：

  1 #!/bin/bash
  2 
  3 # bg.sh
  4 
  5 # Executing commands asynchronously, retrieving their exit codes and outputs upon completion.
  6 
  7 asynch_cmds=
  8 
  9 echo -e "Asynchronous commands:\nPID    FD"
 10 
 11 for i in {1..10}; do
 12         exec {fd}< <(sleep $(( i * 2 )) && echo $RANDOM && exit $i) # Dummy asynchronous task, standard output's stream is redirected to the current shell
 13         asynch_cmds+="$!:$fd " # Append the task's PID and FD to the list of running tasks
 14         
 15         echo "$!        $fd"
 16 done    
 17 
 18 echo -e "\nExit codes and outputs:\nPID       FD      EXIT    OUTPUT"
 19 
 20 while [[ ${#asynch_cmds} -gt 0 ]]; do # While the list of running tasks isn't empty
 21         
 22         for asynch_cmd in $asynch_cmds; do # For each to in thhe list
 23                 
 24                 pid=${asynch_cmd%:*} # Task's PID
 25                 fd=${asynch_cmd#*:} # Task's FD
 26                 
 27                 if ! kill -0 $pid 2>/dev/null; then # If the task ended
 28                         
 29                         wait $pid # Retrieving the task's exit code
 30                         echo -n "$pid   $fd     $?      "
 31                         
 32                         echo "$(cat <&$fd)" # Retrieving the task's output
 33                         
 34                         asynch_cmds=${asynch_cmds/$asynch_cmd /} # Removing the task from the list
 35                 fi
 36         done
 37 done

输出告诉我wait尝试检索每个任务的退出代码失败，预计最后一个运行：

Asynchronous commands:
PID     FD
4348    10
4349    11
4351    12
4353    13
4355    14
4357    15
4359    16
4361    17
4363    18
4365    19

Exit codes and outputs:
PID     FD  EXIT OUTPUT
./bg.sh: line 29: wait: pid 4348 is not a child of this shell
4348    10  127  16010
./bg.sh: line 29: wait: pid 4349 is not a child of this shell
4349    11  127  8341
./bg.sh: line 29: wait: pid 4351 is not a child of this shell
4351    12  127  13814
./bg.sh: line 29: wait: pid 4353 is not a child of this shell
4353    13  127  3775
./bg.sh: line 29: wait: pid 4355 is not a child of this shell
4355    14  127  2309
./bg.sh: line 29: wait: pid 4357 is not a child of this shell
4357    15  127  32203
./bg.sh: line 29: wait: pid 4359 is not a child of this shell
4359    16  127  5907
./bg.sh: line 29: wait: pid 4361 is not a child of this shell
4361    17  127  31849
./bg.sh: line 29: wait: pid 4363 is not a child of this shell
4363    18  127  28920
4365    19  10   28810

命令的输出已完美检索，但我不明白此is not a child of this shell错误来自何处。我肯定做错了什么，因为wait我能够获取要异步运行的最后一个命令的退出代码。

有人知道这个错误是从哪里来的吗？我对这个问题的解决方案有缺陷吗，还是我误解了 bash 的行为？

答案1

出现此错误信息的原因是，您尝试等待的特定 PID 的进程已经完成了从未作为异步进程运行。exec …结果为何会$!被填充我不得而知。您可以使用无法到达的 PID：

$ wait $(($(cat /proc/sys/kernel/pid_max) + 1))
bash: wait: pid 32769 is not a child of this shell

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