问题
If you are writing a multi-threaded application that uses system/library calls that make use of errno to indicate the error type, is there a safe way to use errno? If not, is there some other way to indicate the type of error that occurred rather than just that an error has occurred?
回答1:
If your standard library is multithread aware, then it probably has a #define that changes errno into a function call that returns a thread-local error return value. However, to use this you generally must include <errno.h>, rather than relying on an extern declaration.
I found an article Thread-safety and POSIX.1 which addresses this very question.
回答2:
man errno says:
errno is defined by the ISO C standard to be a modifiable lvalue of type int, and must not be explicitly declared; errno may be a macro. errno is thread-local; setting it in one thread does not affect its value in any other thread.
来源：https://stackoverflow.com/questions/449778/is-there-a-way-to-use-errno-safely-in-a-multi-threaded-application