[glib] gsignal: remove some pointless locking

[Matthias Clasen <matthiasc src gnome org>]

commit 3d1d49177bc577e4c0d4ec2d73b96db09e4d5be3
Author: Ryan Lortie <desrt desrt ca>
Date:   Thu Feb 21 17:48:04 2013 +0000

    gsignal: remove some pointless locking
    
    We previously hold a lock in the loop that collects the arguments for
    g_signal_emit(), which we drop before calling into the argument
    collection functions and reacquire again at the bottom of the loop (ie:
    one release/acquire pair for each argument collected).  To make matters
    worse, the lock is just released again after the loop.
    
    Presumably that was done to protect the access to the parameter array,
    but it's pretty unlikely that this is needed because the only way it
    changes is if the signal is unloaded.  That only happens when unloading
    types which is quite unlikely to happen while we are emitting on an
    instance of that type (and, as an aside, never happens anymore anyway).
    
    If we move the unlock below the loop up above it and remove the
    acquire/release pair from the loop, we improve performance in the new
    arg-collecting performance tests by ~15% (more like ~18% in the case
    where we only emit to one handler -- where argument collection dominates
    more).
    
    https://bugzilla.gnome.org/show_bug.cgi?id=694380

 gobject/gsignal.c |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)
---
diff --git a/gobject/gsignal.c b/gobject/gsignal.c
index f4686bd..7fb98b5 100644
--- a/gobject/gsignal.c
+++ b/gobject/gsignal.c
@@ -3286,6 +3286,7 @@ g_signal_emit_valist (gpointer instance,
          return;
        }
     }
+  SIGNAL_UNLOCK ();
 
   n_params = node->n_params;
   signal_return_type = node->return_type;
@@ -3299,7 +3300,6 @@ g_signal_emit_valist (gpointer instance,
       GType ptype = node->param_types[i] & ~G_SIGNAL_TYPE_STATIC_SCOPE;
       gboolean static_scope = node->param_types[i] & G_SIGNAL_TYPE_STATIC_SCOPE;
 
-      SIGNAL_UNLOCK ();
       G_VALUE_COLLECT_INIT (param_values + i, ptype,
                            var_args,
                            static_scope ? G_VALUE_NOCOPY_CONTENTS : 0,
@@ -3317,9 +3317,7 @@ g_signal_emit_valist (gpointer instance,
 
          return;
        }
-      SIGNAL_LOCK ();
     }
-  SIGNAL_UNLOCK ();
 
   instance_and_params->g_type = 0;
   g_value_init (instance_and_params, G_TYPE_FROM_INSTANCE (instance));