PR python/19293 - invalidate frame cache when unwinders change

PR python/19293 notes that when a Python unwinder is disabled, the
frame cache is not invalidated.  This means that disabling an unwinder
doesn't have any immediate effect -- but in my experience it's often
the case that I want to enable or disable an unwinder in order to see
what happens.

This patch adds a new gdb.invalidate_cached_frames function and
arranges for the relevant bits of library code to call it.  I've only
partially documented this function, considering a warning sufficient
without going into all the reasons ordinary code should not call it.
The name of the new function was taken from a comment in frame.h next
to reinit_frame_cache.

No new test as I think the updates to the existing test are sufficient
to show that the code is working as intended.

Built and regtested on x86-64 Fedora 23.

2016-07-12  Tom Tromey  <tom@tromey.com>

	PR python/19293:
	* python/lib/gdb/command/unwinders.py (do_enable_unwinder): Call
	gdb.invalidate_cached_frames.
	* python/lib/gdb/unwinder.py (register_unwinder): Call
	gdb.invalidate_cached_frames.
	* python/python.c (gdbpy_invalidate_cached_frames): New function.
	(python_GdbMethods): Add entry for invalidate_cached_frames.

2016-07-12  Tom Tromey  <tom@tromey.com>

	PR python/19293:
	* python.texi (Frames In Python): Document
	gdb.invalidate_cached_frames.

2016-07-12  Tom Tromey  <tom@tromey.com>

	PR python/19293:
	* gdb.python/py-unwind-maint.exp: Update tests.

3 files changed, 18 insertions, 0 deletions

diff --git a/gdb/python/lib/gdb/command/unwinders.py b/gdb/python/lib/gdb/command/unwinders.py
index a9b9d8a..8fd0136 100644
--- a/gdb/python/lib/gdb/command/unwinders.py
+++ b/gdb/python/lib/gdb/command/unwinders.py
@@ -136,6 +136,8 @@ def do_enable_unwinder(arg, flag):
         if locus_re.match(objfile.filename):
             total += do_enable_unwinder1(objfile.frame_unwinders, name_re,
                                          flag)
+    if total > 0:
+        gdb.invalidate_cached_frames()
     print("%d unwinder%s %s" % (total, "" if total == 1 else "s",
                                 "enabled" if flag else "disabled"))
 
diff --git a/gdb/python/lib/gdb/unwinder.py b/gdb/python/lib/gdb/unwinder.py
index 14b2758..67a37cb 100644
--- a/gdb/python/lib/gdb/unwinder.py
+++ b/gdb/python/lib/gdb/unwinder.py
@@ -92,3 +92,4 @@ def register_unwinder(locus, unwinder, replace=False):
                                    unwinder.name)
         i += 1
     locus.frame_unwinders.insert(0, unwinder)
+    gdb.invalidate_cached_frames()
diff --git a/gdb/python/python.c b/gdb/python/python.c
index 3a272a9..621e201 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -885,6 +885,15 @@ gdbpy_find_pc_line (PyObject *self, PyObject *args)
   return result;
 }
 
+/* Implementation of gdb.invalidate_cached_frames.  */
+
+static PyObject *
+gdbpy_invalidate_cached_frames (PyObject *self, PyObject *args)
+{
+  reinit_frame_cache ();
+  Py_RETURN_NONE;
+}
+
 /* Read a file as Python code.
    This is the extension_language_script_ops.script_sourcer "method".
    FILE is the file to load.  FILENAME is name of the file FILE.
@@ -2071,6 +2080,12 @@ Return the selected inferior object." },
   { "inferiors", gdbpy_inferiors, METH_NOARGS,
     "inferiors () -> (gdb.Inferior, ...).\n\
 Return a tuple containing all inferiors." },
+
+  { "invalidate_cached_frames", gdbpy_invalidate_cached_frames, METH_NOARGS,
+    "invalidate_cached_frames () -> None.\n\
+Invalidate any cached frame objects in gdb.\n\
+Intended for internal use only." },
+
   {NULL, NULL, 0, NULL}
 };