Spring's state machine thread is not safe

recently, I am choosing a state machine engine, in which it is said on the Internet that spring"s state machine has thread safety problems, but I don"t understand it. Can you give me a specific example to illustrate it?

Mar.17,2021

is a thread safety issue for singleton mode.
there is a detailed explanation in this article: https://codeshelper.com/a/11.
@ answer in the wind

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
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MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b39bab-2c1ad.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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