send_ldap_ber mutex overhead

[Howard Chu]

The attached patch avoids grabbing conn->c_mutex unnecessarily. Testing on my 
laptop with test008 and SLAPD_DEBUG=0 shows a 33% speedup. Before moving ahead 
with this patch, I'd like to verify that ITS#5835 doesn't reappear. Anyone 
able to test and report back?
--
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/
--- result.c    2013-01-07 05:33:58.000000000 -0800
+++ result.c.N  2013-01-07 05:33:48.000000000 -0800
@@ -320,6 +320,7 @@
        while( 1 ) {
                int err;
 
+#if 0
                /* lock the connection */ 
                if ( ldap_pvt_thread_mutex_trylock( &conn->c_mutex )) {
                        if ( !connection_valid(conn)) {
@@ -334,9 +335,12 @@
                        }
                        continue;
                }
+#endif
 
                if ( ber_flush2( conn->c_sb, ber, LBER_FLUSH_FREE_NEVER ) == 0 
) {
+#if 0
                        ldap_pvt_thread_mutex_unlock( &conn->c_mutex );
+#endif
                        ret = bytes;
                        break;
                }
@@ -356,6 +360,7 @@
                        conn->c_writers--;
                        conn->c_writing = 0;
                        ldap_pvt_thread_mutex_unlock( &conn->c_write1_mutex );
+                       ldap_pvt_thread_mutex_lock( &conn->c_mutex );
                        connection_closing( conn, "connection lost on write" );
 
                        ldap_pvt_thread_mutex_unlock( &conn->c_mutex );
@@ -368,7 +373,9 @@
                slapd_set_write( conn->c_sd, 2 );
 
                ldap_pvt_thread_mutex_unlock( &conn->c_write1_mutex );
+#if 0
                ldap_pvt_thread_mutex_unlock( &conn->c_mutex );
+#endif
                ldap_pvt_thread_pool_idle( &connection_pool );
                ldap_pvt_thread_cond_wait( &conn->c_write2_cv, 
&conn->c_write2_mutex );
                conn->c_writewaiter = 0;