Add the option { hibernate_after, int() } to ssl:connect and ssl:listen

When making an SSL connection (either as client or as server), the
process implementing the connection may use as much as hundreds of
kilobytes of memory, even when idle. This is problematic for any
application maintaining more than just a few SSL connections.

This patch introduces the option { hibernate_after, int() } to the
ssl:connect and ssl:listen functions, making the SSL connection
process go into hibernation after the specified number of milliseconds
of inactivity. This will reduce the memory used by the process to
just a few hundred bytes, making applications with thousands or
more SSL connections feasible, as long as most of the connections
are idle for most of the time (which is typically the case).

The approach of making the process go into hibernation only after
some time of inactivity was chosen because hibernation incurs some
CPU usage, and it is therefore not desirable for a process to
hibernate after each call.

1 files changed, 5 insertions, 1 deletions

diff --git a/lib/ssl/src/ssl_internal.hrl b/lib/ssl/src/ssl_internal.hrl
index 715941e3ad..c28daa271e 100644
--- a/lib/ssl/src/ssl_internal.hrl
+++ b/lib/ssl/src/ssl_internal.hrl
@@ -98,7 +98,11 @@
 	  reuse_sessions, % boolean()
 	  renegotiate_at,
 	  secure_renegotiate,
-	  debug           %
+	  debug,
+	  hibernate_after % undefined if not hibernating,
+                          % or number of ms of inactivity
+			  % after which ssl_connection will
+                          % go into hibernation
 	  }).
 
 -record(socket_options,