Use per-agent locks and GWeakRefs in callbacks from timeout sources

Work on libnice's bug #1 in Gitlab. This work is composed of multiple
merged parts:

- "Global lock contention removed"
Phabricator D1900: https://phabricator.freedesktop.org/D1900
By @nifigase
Opened in GitLab as Merge Request !12

- "agent: properly handle NiceAgent ref in callbacks from timeout
sources"
Phabricator D1898: https://phabricator.freedesktop.org/D1898
By @mparis
This patch was itself based upon a previous version of the work done in
D1900. After the switch of hosting, it got lost.

On top of these, additions to follow some review comments from @ocrete:
- https://phabricator.freedesktop.org/D1900#40412
- https://phabricator.freedesktop.org/D1898#39332

1 files changed, 8 insertions, 4 deletions

diff --git a/socket/tcp-bsd.c b/socket/tcp-bsd.c
index 285d323..d5dd633 100644
--- a/socket/tcp-bsd.c
+++ b/socket/tcp-bsd.c
@@ -60,6 +60,7 @@
 #define TCP_NODELAY 1
 
 typedef struct {
+  GMutex mutex;
   NiceAddress remote_addr;
   GQueue send_queue;
   GMainContext *context;
@@ -101,6 +102,7 @@ nice_tcp_bsd_socket_new_from_gsock (GMainContext *ctx, GSocket *gsock,
 
   if (ctx == NULL)
     ctx = g_main_context_default ();
+  g_mutex_init (&priv->mutex);
   priv->context = g_main_context_ref (ctx);
   priv->remote_addr = *remote_addr;
   priv->error = FALSE;
@@ -227,6 +229,8 @@ socket_close (NiceSocket *sock)
   if (priv->context)
     g_main_context_unref (priv->context);
 
+  g_mutex_clear (&priv->mutex);
+
   g_slice_free(TcpPriv, sock->priv);
 }
 
@@ -424,12 +428,12 @@ socket_send_more (
   NiceSocket *sock = (NiceSocket *) data;
   TcpPriv *priv = sock->priv;
 
-  agent_lock ();
+  g_mutex_lock (&priv->mutex);
 
   if (g_source_is_destroyed (g_main_current_source ())) {
     nice_debug ("Source was destroyed. "
         "Avoided race condition in tcp-bsd.c:socket_send_more");
-    agent_unlock ();
+    g_mutex_unlock (&priv->mutex);
     return FALSE;
   }
 
@@ -441,7 +445,7 @@ socket_send_more (
     g_source_unref (priv->io_source);
     priv->io_source = NULL;
 
-    agent_unlock ();
+    g_mutex_unlock (&priv->mutex);
 
     if (priv->writable_cb)
       priv->writable_cb (sock, priv->writable_data);
@@ -449,6 +453,6 @@ socket_send_more (
     return FALSE;
   }
 
-  agent_unlock ();
+  g_mutex_unlock (&priv->mutex);
   return TRUE;
 }