libssh_tutor_threads(3)

NAME
libssh_tutor_threads - Chapter 8: Threads with libssh

How to use libssh with threads

libssh may be used in multithreaded applications, but under several conditions :

•   Threading must be initialized during the initialization of libssh. This initialization must be done outside of any threading context.

•   If pthreads is being used by your application (or your framework's backend), you must link with libssh_threads dynamic library and initialize threading with the ssh_threads_pthreads threading object.

•   If an other threading library is being used by your application, you must implement all the methods of the ssh_threads_callbacks_struct structure and initialize libssh with it.

•   At all times, you may use different sessions inside threads, make parallel connections, read/write on different sessions and so on. You cannot use a single session (or channels for a single session) in several threads at the same time. This will most likely lead to internal state corruption. This limitation is being worked out and will maybe disappear later.

  Initialization of threads
To initialize threading, you must first select the threading model you want to use, using ssh_threads_set_callbacks(), then call ssh_init().

#include <libssh/callbacks.h>
...
ssh_threads_set_callbacks(ssh_threads_get_noop());
ssh_init();

ssh_threads_noop is the threading structure that does nothing. It's the threading callbacks being used by default when you're not using threading.

  Using libpthread with libssh
If your application is using libpthread, you may simply use the libpthread threading backend:

#include <libssh/callbacks.h>
...
ssh_threads_set_callbacks(ssh_threads_get_pthread());
ssh_init();

However, you must be sure to link with the library ssh_threads. If you're using gcc, you must use the commandline

gcc -o output input.c -lssh -lssh_threads

  Using another threading library
You must find your way in the ssh_threads_callbacks_struct structure. You must implement the following methods :

•   mutex_lock

•   mutex_unlock

•   mutex_init

•   mutex_destroy

•   thread_id

libgcrypt 1.6 and bigger backend does not support custom callback. Using anything else than pthreads (ssh_threads_get_pthread()) here will fail. Good luck !