libssh2 library is not thread safe

[anonymous]

By default, there is no "-D_REENTRANT" flag passed to the C preprocessor (nor any -mt (Sun Studio) or -pthreads (gcc) option to the C compiler).
Note: I'm using libssh2 on Solaris 9/10, using Sun Studio 12.

Referencing errno in many pieces of code makes the whole library not thread safe (libssh2_session_startup() for example). There are many EAGAIN errors that are now thrown internally (because of new non-blocking sockets in 1.1), but unfortunately, the errno value is not correctly accessed, leading to undefined behaviour. This can be "easily" reproduced using something like (compiled in a thread safe manner):

Th.1: set errno
Th.1: detach thread 2
Th.2: establish an SSH connection. libssh2_session_startup() will usually fail.

I've passed CPPFLAGS="-D_REENTRANT" to the configure script, and things seem now to be OK.

Miscellaneous defects of the "configure" script:

• Specifying LDFLAGS="-mt -pthreads" does not pass these options to the ld linker.
• Specifying --disable-debug still compiles with "-g".

[bagder]

The configure script obviously needs to check for _REENTRANT. I'm confident we can get some inspiration and code from here:

​http://curl.haxx.se/lxr/source/m4/curl-reentrant.m4#L390

You able to provide a patch?

[p82420]

Hello,

Sorry, but I'm not really confident with configure.in, m4 macros and all that stuff.

[bagder]

I've now committed a fix for this in the git repo. It'd be great if you tried it.

The fix will be included in the June 5 and later snapshots from => ​http://libssh2.haxx.se/snapshots.html

[bagder]

Thanks for your report and help in improving libssh2!

A fix has just been committed to the source code repo, this case is now considered fixed and closed!