Manage objfiles with shared_ptr

This changes objfiles to be managed using a shared_ptr.  shared_ptr is
chosen because it enables the use of objfiles in background threads.

The simplest way to do this was to introduce a new iterator that will
return the underlying objfile, rather than a shared_ptr.  (I also
tried changing the rest of gdb to use shared_ptr, but this was quite
large; and to using intrusive reference counting, but this also was
tricky.)

gdb/ChangeLog
2019-12-12  Tom Tromey  <tom@tromey.com>

	* progspace.h (objfile_list): New typedef.
	(class unwrapping_objfile_iterator)
	(struct unwrapping_objfile_range): Newl
	(struct program_space) <objfiles_range>: Change type.
	<objfiles>: Change return type.
	<add_objfile>: Change type of "objfile" parameter.
	<objfiles_list>: Now a list of shared_ptr.
	* progspace.c (program_space::add_objfile): Change type of
	"objfile".  Update.
	(program_space::remove_objfile): Update.
	* objfiles.h (struct objfile) <~objfile>: Make public.
	* objfiles.c (objfile::make): Update.
	(objfile::unlink): Don't call delete.

Change-Id: I6fb7fbf06efb7cb7474c525908365863eae27eb3

1 files changed, 10 insertions, 3 deletions

diff --git a/gdb/objfiles.h b/gdb/objfiles.h
index 3424055..f0ee803 100644
--- a/gdb/objfiles.h
+++ b/gdb/objfiles.h
@@ -28,12 +28,14 @@
 #include "registry.h"
 #include "gdb_bfd.h"
 #include "psymtab.h"
+#include <atomic>
 #include <bitset>
 #include <vector>
 #include "gdbsupport/next-iterator.h"
 #include "gdbsupport/safe-iterator.h"
 #include "bcache.h"
 #include "gdbarch.h"
+#include "gdbsupport/refcounted-object.h"
 
 struct htab;
 struct objfile_data;
@@ -399,11 +401,16 @@ private:
   /* The only way to create an objfile is to call objfile::make.  */
   objfile (bfd *, const char *, objfile_flags);
 
-  /* The only way to free an objfile is via 'unlink'.  */
-  ~objfile ();
-
 public:
 
+  /* Normally you should not call delete.  Instead, call 'unlink' to
+     remove it from the program space's list.  In some cases, you may
+     need to hold a reference to an objfile that is independent of its
+     existence on the program space's list; for this case, the
+     destructor must be public so that shared_ptr can reference
+     it.  */
+  ~objfile ();
+
   /* Create an objfile.  */
   static objfile *make (bfd *bfd_, const char *name_, objfile_flags flags_,
 			objfile *parent = nullptr);