bash 防止 printf 中断另一个 printf

Question

我有以下测试脚本。

#!/bin/bash

function foo {
  printf "Test line break: $1\nafter line break\n\n"
}

for VARIABLE in {1..30}
do
  foo $VARIABLE &
done
wait

现在我执行了几次脚本，有时输出看起来像这样：

Test line break: 15
Test line break: 14
after line break: 14
after line break: 15


Test line break: 16
after line break: 16

而不是预期的：

Test line break: 15
after line break: 15

Test line break: 14
after line break: 14

Test line break: 16
after line break: 16

如何防止 printf“中断”另一个 printf，但仍在后台运行它？

对我来说，问题似乎是 printf 中的“\n”。

Answer 1

事实上，你需要一个互斥锁：

每个子shell都会同时访问同/dev/stdout一个父shell，所以即使在同一个函数内部也不能保证顺序。为了确保它，您需要一个强制互斥的锁，即：在/dev/stdout释放锁之前，所有其他进程都不会开始写入。

#!/bin/bash

function foo {
lockdir=/tmp/myscript.lock
 mkdir "$lockdir" 2>/dev/null
while [ $? -ne 0 ]; do mkdir "$lockdir" 2>/dev/null; done
printf "Test line break: $1\nafter line break: $1\n\n"
rm -rf $lockdir
}

for VARIABLE in {1..30}
do
  foo $VARIABLE &
done
wait

结果如下：

$ bash plop1 2>/dev/null
Test line break: 5
after line break: 5

Test line break: 3
after line break: 3

Test line break: 11
after line break: 11

Test line break: 23
after line break: 23

Test line break: 14
after line break: 14

Test line break: 17
after line break: 17

Test line break: 24
after line break: 24

Test line break: 21
after line break: 21

Test line break: 27
after line break: 27

Test line break: 6
after line break: 6

Test line break: 2
after line break: 2

Test line break: 9
after line break: 9

Test line break: 26
after line break: 26

Test line break: 29
after line break: 29

Test line break: 20
after line break: 20

Test line break: 1
after line break: 1

Test line break: 12
after line break: 12

Test line break: 4
after line break: 4

Test line break: 13
after line break: 13

Test line break: 10
after line break: 10

Test line break: 15
after line break: 15

Test line break: 28
after line break: 28

Test line break: 25
after line break: 25

Test line break: 19
after line break: 19

Test line break: 18
after line break: 18

Test line break: 8
after line break: 8

Test line break: 7
after line break: 7

Test line break: 16
after line break: 16

Test line break: 22
after line break: 22

Test line break: 30
after line break: 30