SSL_SESSION_free() decrements the reference count of session and removes
the SSL_SESSION structure pointed to by session and frees up the allocated
memory, if the the reference count has reached 0.
NOTES
SSL_SESSION objects are allocated, when a TLS/SSL handshake operation
is successfully completed. Depending on the settings, see
SSL_CTX_set_session_cache_mode(3),
the SSL_SESSION objects are internally referenced by the SSL_CTX and
linked into its session cache. SSL objects may be using the SSL_SESSION object;
as a session may be reused, several SSL objects may be using one SSL_SESSION
object at the same time. It is therefore crucial to keep the reference
count (usage information) correct and not delete a SSL_SESSION object
that is still used, as this may lead to program failures due to
dangling pointers. These failures may also appear delayed, e.g.
when an SSL_SESSION object was completely freed as the reference count
incorrectly became 0, but it is still referenced in the internal
session cache and the cache list is processed during a
SSL_CTX_flush_sessions(3) operation.
SSL_SESSION_free() must only be called for SSL_SESSION objects, for
which the reference count was explicitly incremented (e.g.
by calling SSL_get1_session(), see SSL_get_session(3))
or when the SSL_SESSION object was generated outside a TLS handshake
operation, e.g. by using d2i_SSL_SESSION(3).
It must not be called on other SSL_SESSION objects, as this would cause
incorrect reference counts and therefore program failures.
RETURN VALUES
SSL_SESSION_free() does not provide diagnostic information.
