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From Adel Boutros <adelbout...@live.com>
Subject [Qpid Proton 0.12.2] errno not thread-safe on Solaris
Date Mon, 29 Aug 2016 07:32:46 GMT
Hello,

For some time, we were having random errors on Solaris with proton-c where we would get a
transport error "proton:io connect: Error 0". We were finally able to reproduce it in a multi-threading
environment. It turns out some C/C++ system calls such as opening sockets will set the value
of "errno" and some parts of proton-c code you rely on the value of errno to determine if
the operation was successful or not[1].

The issue is that errno is not thread safe[2] and as a consequence if by the time Thread A
was checking the value of errno, Thread B has set it to something else, the check will fail.

We resolved it by compiling Proton with "-D_REENTRANT" which makes errno thread local variable.

Please note we only got this error on Solaris because on Linux setting "-lpthread" implies
"-D_REENTRANT flag" according to stackoverflow[2].

Do you think this flag could be set by default in the CMakeList of proton to avoid others
having the same issue?

On Solaris:
/usr/include/errno.h

#if defined(_REENTRANT) || defined(_TS_ERRNO) || _POSIX_C_SOURCE - 0 >= 199506L
extern int *___errno();
#define errno (*(___errno()))
#else
extern int errno;
/* ANSI C++ requires that errno be a macro */
#if __cplusplus >= 199711L
#define errno errno
#endif
#endif  /* defined(_REENTRANT) || defined(_TS_ERRNO) */

PS: The code is still the same on 0.14.0. So the error could happen there as well I guess.

Regards,
Adel

[1]: https://github.com/apache/qpid-proton/blob/0.12.2/proton-c/src/posix/io.c (line 187-188)
[2]: http://stackoverflow.com/questions/1694164/is-errno-thread-safe 
[3]: http://stackoverflow.com/questions/875789/gcc-do-i-need-d-reentrant-with-pthreads 
 		 	   		  
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