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?
+9
A:
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.
Greg Hewgill
2009-01-16 07:49:26
+1 you beat me to it.. :)
roe
2009-01-16 07:50:53
Thanks! A quick check in /usr/include/bits/errno.h confirmed that errno is indeed defined to be per-thread when using threads, on my Ubundu machine.
Erik Öjebo
2009-01-16 08:04:36
+4
A:
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.
qrdl
2009-01-16 08:54:40