如果使用第三方程序库，事情会变得更为复杂，因为您永远不知道哪部分程序库是可重入的，哪部分是不可重入的。

Things become even more complicated when you're using a third-party library, because you never know which parts of the library are reentrant and which are not.

youdao

在大部分系统中，malloc和free都不是可重入的，因为它们使用静态数据结构来记录哪些内存块是空闲的。

On most systems, malloc and free are not reentrant, because they use a static data structure that records which memory blocks are free.

youdao

那是因为只有一些系统调用可以安全地调用内部信号：只有可重入的(re - entrant)或者不被信号中断的调用才可以被安全地调用。

That's because only a few system calls can be safely called inside signals. Only calls that are re-entrant or not interruptible by signals can be called safely.

youdao