Lock channels before doing I/O

The debugger's use of channels doesn't support locking, but it
doesn't work on threaded programs anyway.

ocamltest/run_stubs.c

@@ -71,8 +71,10 @@ static void logToChannel(void *voidchannel, const char *fmt, va_list ap)
     if (text == NULL) return;
     if (vsnprintf(text, length, fmt, ap) != length) goto end;
   }
+  Lock(channel);
   caml_putblock(channel, text, length);
   caml_flush(channel);
+  Unlock(channel);
 end:
   free(text);
 }

runtime/backtrace_byt.c

@@ -386,6 +386,7 @@ static void read_main_debug_info(struct debug_info *di)
   if (caml_seek_optional_section(fd, &trail, "DBUG") != -1) {
     chan = caml_open_descriptor_in(fd);
 
+    Lock(chan);
     num_events = caml_getword(chan);
     events = caml_alloc(num_events, 0);
 
@@ -401,6 +402,7 @@ static void read_main_debug_info(struct debug_info *di)
       /* Record event list */
       Store_field(events, i, evl);
     }
+    Unlock(chan);
 
     caml_close_channel(chan);
 

runtime/caml/io.h

@@ -65,7 +65,7 @@ enum {
 */
 
 /* Functions and macros that can be called from C.  Take arguments of
-   type struct channel *.  No locking is performed. */
+   type struct channel *.  The channel must be locked before calling these. */
 
 #define caml_putch(channel, ch) do{                                       \
   if ((channel)->curr >= (channel)->end) caml_flush_partial(channel);     \

runtime/debugger.c

@@ -141,6 +141,12 @@ static void open_connection(void)
 #endif
   dbg_in = caml_open_descriptor_in(dbg_socket);
   dbg_out = caml_open_descriptor_out(dbg_socket);
+  /* The code in this file does not bracket channel I/O operations with
+     Lock and Unlock, so fail if those are not no-ops. */
+  if (caml_channel_mutex_lock != NULL ||
+      caml_channel_mutex_unlock != NULL ||
+      caml_channel_mutex_unlock_exn != NULL)
+    caml_fatal_error("debugger does not support channel locks");
   if (!caml_debugger_in_use) caml_putword(dbg_out, -1); /* first connection */
 #ifdef _WIN32
   caml_putword(dbg_out, _getpid());

runtime/startup_byt.c

@@ -444,7 +444,9 @@ CAMLexport void caml_main(char_os **argv)
   /* Load the globals */
   caml_seek_section(fd, &trail, "DATA");
   chan = caml_open_descriptor_in(fd);
+  Lock(chan);
   caml_global_data = caml_input_val(chan);
+  Unlock(chan);
   caml_close_channel(chan); /* this also closes fd */
   caml_stat_free(trail.section);
   /* Ensure that the globals are in the major heap. */