C标准库线程中的函数安全吗? [英] Are functions in the C standard library thread safe?
问题描述
在哪里可以得到明确的答案，我的memcpy(使用Ubuntu随附的eglibc实现)是否是线程安全的? -老实说，我确实没有在文档中找到明确的是"或否".
Where can I get a definitive answer, whether my memcpy (using the eglibc implementation that comes with Ubuntu) is thread safe? - Honestly, I really did not find a clear YES or NO in the docs.
顺便说一句，线程安全"是指只要可以安全地同时复制一个字节的日期字节，就可以安全地并发使用memcpy.至少如果将只读数据复制到不重叠的区域，则应该可以做到这一点.
By the way, with "thread safe" I mean it is safe to use memcpy concurrently whenever it would be safe to copy the date byte for byte concurrently. This should be possible at least if read-only data are copied to regions that do not overlap.
Ideally I would like to see something like the lists at the bottom of this page in the ARM compiler docs.
推荐答案
您可以在2.9.1 Thread-Safety章中找到此列表:http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_09_01
You can find that list here, at chapter 2.9.1 Thread-Safety : http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_09_01
也就是说，这是posix 不要求是线程安全的函数的列表.所有其他功能都必须是线程安全的. Posix包括标准C库和典型的"unix"接口. (完整列表在这里， http://pubs.opengroup.org/onlinepubs/9699919799/functions/contents.html )
That is, this is a list over functions that posix does not require to be thread safe. All other functions are required to be thread safe. Posix includes the standard C library and the typical "unix" interfaces. (Full list here, http://pubs.opengroup.org/onlinepubs/9699919799/functions/contents.html)
memcpy()由posix指定，但不属于2.9.1中的列表，因此可以认为是线程安全的.
memcpy() is specified by posix, but not part of the list in 2.9.1, and can therefore be considered thread safe.
Linux上的各种环境至少尝试尽其所能实现posix-即使posix不需要linux/glibc上的功能，它也可能是线程安全的-尽管很少记录.对于posix所不具备的其他功能/库，您只需保留其作者所记录的内容...
The various environments on linux at least tries to implement posix to the best of its abilities - The functions on linux/glibc might be thread-safe even if posix doesn't require it to be - though this is rarely documented. For other functions/libraries than what posix covers, you are left with what their authors have documented...
据我所知，posix将线程安全等同于可重入，并保证没有内部数据竞争.但是，您应对可能的外部数据竞赛负责-例如保护自己免于致电例如memcpy()具有可能同时更新的内存.
From what I can tell, posix equates thread safety with reentrancy, and guarantees there is no internal data races. You, however, are responsible for the possible external data races - such as protecting yourself from calling e.g. memcpy() with memory that might be updated concurrently.
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