Ticket #99 (closed defect)

Opened 8 years ago

Last modified 8 years ago

libssh2 library is not thread safe

Reported by: anonymous Owned by: bagder
Priority: normal Milestone:
Component: misc Version:
Keywords: Cc: bagder, p82420
Blocked By: Blocks:


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".

Change History

comment:1 Changed 8 years ago by bagder

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


You able to provide a patch?

comment:2 Changed 8 years ago by p82420


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

comment:3 Changed 8 years ago by 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

comment:4 Changed 8 years ago by 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!

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