Alan Conway commented on PROTON-992:

OK, been looking at the cyrus sasl code. I believe that all we need to do is 
separate the per-process init/done logic and we are ok. From my scan it looks 
like any function of the form `sasl_*(sasl_conn_t...)` is safe to call if you 
serialize access on (at least) a per-connection basis, which all proton 
applications already do since proton itself requires serialization at least 

I believe when we separate the process wide init/shutdown code from the 
per-connection sasl code, all the dangerous `sasl_get_` functions will end up 
in the per-process code where they are not dangerous. The man page says that 
otherwise "most of libsasl is MT safe", which by my scan of the code means "it 
is safe to call sasl functions that take a sasl_conn_t parameter concurrently 
for different instances of sasl_conn_t. Nothing else should ever be called 

I would completely ignore sasl_set_mutex, it looks like something somebody 
thought was a Good Idea but never actually implemented. The only place a mutex 
is actually locked is:

  /* serialize disposes. this is necessary because we can't
     dispose of conn->mutex if someone else is locked on it
     xxx there probably is a better way to do this */
  result = sasl_MUTEX_LOCK(dispose_mutex);

Hum, so we're using mutexes only to solve a problem created by the use of 
mutexes? My answer to "xxx" is yes, there is a better way: don't litter your 
code with mutexes that you don't even ever lock!!! There is no sasl_set_mutex 
man page in the latest source tarball so I'm guessing the folks at Cyrus 
realized it was a daft idea and are backing away, slowly.
As I read it, dispose is safe if you are serialized per connection.  Of course 
I could be wrong, I have been before...
Of course I could be wrong.

> Proton's use of Cyrus SASL is not thread-safe.
> ----------------------------------------------
>                 Key: PROTON-992
>                 URL: https://issues.apache.org/jira/browse/PROTON-992
>             Project: Qpid Proton
>          Issue Type: Bug
>          Components: proton-c
>    Affects Versions: 0.10
>            Reporter: michael goulish
>            Assignee: michael goulish
>            Priority: Critical
> Documentation for the Cyrus SASL library says that the library is believed to 
> be thread-safe only if the code that uses it meets several requirements.
> The requirements are:
>     * you supply mutex functions (see sasl_set_mutex())
>     * you make no libsasl calls until sasl_client/server_init() completes
>     * no libsasl calls are made after sasl_done() is begun
>     * when using GSSAPI, you use a thread-safe GSS / Kerberos 5 library.
> It says explicitly that that sasl_set* calls are not thread safe, since they 
> set global state.
> The proton library makes calls to sasl_set* functions in :
>           pni_init_client()
>           pni_init_server(), and
>           pni_process_init()
> Since those are internal functions, there is no way for code that uses Proton 
> to lock around those calls.
> I think proton needs a new API call to let applications call 
> sasl_set_mutex().  Or something.
> We probably also need other protections to meet the other requirements 
> specified in the Cyrus documentation (and quoted above).

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