Protect static data by mutex

ot_livesync.c

@@ -46,13 +46,14 @@ static int64    g_socket_in = -1;
 /* For incoming packets */
 static int64    g_socket_out = -1;
 
+static pthread_mutex_t g_outbuf_mutex = PTHREAD_MUTEX_INITIALIZER;
 char            g_outbuf[LIVESYNC_OUTGOING_BUFFSIZE_PEERS];
 static size_t   g_outbuf_data;
 static ot_time  g_next_packet_time;
 
 static pthread_t thread_id;
 void livesync_init( ) {
-  
+
   if( g_socket_in == -1 )
     exerr( "No socket address for live sync specified." );
 
@@ -62,7 +63,7 @@ void livesync_init( ) {
   g_outbuf_data = sizeof( g_tracker_id ) + sizeof( uint32_t );
 
   g_next_packet_time = g_now_seconds + LIVESYNC_MAXDELAY;
-  
+
   pthread_create( &thread_id, NULL, livesync_worker, NULL );
 }
 
@@ -105,10 +106,20 @@ void livesync_bind_mcast( ot_ip6 ip, uint16_t port) {
   socket_mcloop4(g_socket_out, 0);
 }
 
+/* Caller MUST hold g_outbuf_mutex. Returns with g_outbuf_mutex unlocked */
 static void livesync_issue_peersync( ) {
-  socket_send4(g_socket_out, g_outbuf, g_outbuf_data, groupip_1, LIVESYNC_PORT);
+  char   mycopy[LIVESYNC_OUTGOING_BUFFSIZE_PEERS];
+  size_t data = g_outbuf_data;
+
+  memcpy( mycopy, g_outbuf, data );
   g_outbuf_data = sizeof( g_tracker_id ) + sizeof( uint32_t );
   g_next_packet_time = g_now_seconds + LIVESYNC_MAXDELAY;
+
+  /* From now this thread has a local copy of the buffer and
+     has modified the protected element */
+  pthread_mutex_unlock(&g_outbuf_mutex);
+
+  socket_send4(g_socket_out, mycopy, data, groupip_1, LIVESYNC_PORT);
 }
 
 static void livesync_handle_peersync( struct ot_workstruct *ws ) {
@@ -140,13 +151,17 @@ static void livesync_handle_peersync( struct ot_workstruct *ws ) {
    enough */
 void livesync_ticker( ) {
   /* livesync_issue_peersync sets g_next_packet_time */
+  pthread_mutex_lock(&g_outbuf_mutex);
   if( g_now_seconds > g_next_packet_time &&
      g_outbuf_data > sizeof( g_tracker_id ) + sizeof( uint32_t ) )
     livesync_issue_peersync();
+  else
+    pthread_mutex_unlock(&g_outbuf_mutex);
 }
 
 /* Inform live sync about whats going on. */
 void livesync_tell( struct ot_workstruct *ws ) {
+  pthread_mutex_lock(&g_outbuf_mutex);
 
   memcpy( g_outbuf + g_outbuf_data, ws->hash, sizeof(ot_hash) );
   memcpy( g_outbuf + g_outbuf_data + sizeof(ot_hash), &ws->peer, sizeof(ot_peer) );
@@ -155,6 +170,8 @@ void livesync_tell( struct ot_workstruct *ws ) {
 
   if( g_outbuf_data >= LIVESYNC_OUTGOING_BUFFSIZE_PEERS - LIVESYNC_OUTGOING_WATERMARK_PEERS )
     livesync_issue_peersync();
+  else
+    pthread_mutex_unlock(&g_outbuf_mutex);
 }
 
 static void * livesync_worker( void * args ) {
@@ -162,11 +179,11 @@ static void * livesync_worker( void * args ) {
   ot_ip6 in_ip; uint16_t in_port;
 
   (void)args;
-  
+
   /* Initialize our "thread local storage" */
   ws.inbuf   = ws.request = malloc( LIVESYNC_INCOMING_BUFFSIZE );
   ws.outbuf  = ws.reply   = 0;
-  
+
   memcpy( in_ip, V4mappedprefix, sizeof( V4mappedprefix ) );
 
   while( 1 ) {