Support buffer objects as handles in Inferior.thread_from_thread_handle()

InferiorThread.handle() returns a python bytes object.  We'd like to
be able to pass the output of this function, a thread handle, to
Inferior.thread_from_thread_handle().  Up to now,
thread_from_thread_handle() expects to receive a gdb.Value input.
This commit adds support to also allow a python buffer object to be
passed as the handle.

infpy_thread_from_thread_handle() calls find_thread_by_handle() which
has the obvious functionality.  It used to pass the thread handle via
a struct value pointer.  I've revised this interface to instead pass a
gdb::array_view<const gdb_byte> object.  (Thanks to Tom Tromey for
suggesting this data structure over an earlier version which passed a
gdb_byte pointer and length.)

gdb/ChangeLog:

	* gdbthread.h (find_thread_by_handle): Revise declaration.
	* thread.c (find_thread_by_handle): Likewise.  Adjust
	implementation too.
	* python/py-inferior.c (infpy_thread_from_thread_handle): Add
	support for buffer objects as handles.

gdb/ChangeLog

@@ -1,3 +1,11 @@
+2019-04-08  Kevin Buettner  <kevinb@redhat.com>
+
+	* gdbthread.h (find_thread_by_handle): Revise declaration.
+	* thread.c (find_thread_by_handle): Likewise.  Adjust
+	implementation too.
+	* python/py-inferior.c (infpy_thread_from_thread_handle): Add
+	support for buffer objects as handles.
+
 2019-04-08  Kevin Buettner  <kevinb@redhat.com>
 
 	* python/py-infthread.c (thpy_thread_handle): New function.

gdb/gdbthread.h

@@ -486,8 +486,8 @@ extern struct thread_info *find_thread_ptid (inferior *inf, ptid_t ptid);
 struct thread_info *find_thread_global_id (int global_id);
 
 /* Find thread by thread library specific handle in inferior INF.  */
-struct thread_info *find_thread_by_handle (struct value *thread_handle,
+struct thread_info *find_thread_by_handle
-					   struct inferior *inf);
+  (gdb::array_view<const gdb_byte> handle, struct inferior *inf);
 
 /* Finds the first thread of the specified inferior.  */
 extern struct thread_info *first_thread_of_inferior (inferior *inf);

gdb/python/py-inferior.c

@@ -770,7 +770,25 @@ infpy_thread_from_thread_handle (PyObject *self, PyObject *args, PyObject *kw)
   if (! gdb_PyArg_ParseTupleAndKeywords (args, kw, "O", keywords, &handle_obj))
     return NULL;
 
-  if (!gdbpy_is_value_object (handle_obj))
+  const gdb_byte *bytes;
+  size_t bytes_len;
+  Py_buffer_up buffer_up;
+  Py_buffer py_buf;
+
+  if (PyObject_CheckBuffer (handle_obj)
+      && PyObject_GetBuffer (handle_obj, &py_buf, PyBUF_SIMPLE) == 0)
+    {
+      buffer_up.reset (&py_buf);
+      bytes = (const gdb_byte *) py_buf.buf;
+      bytes_len = py_buf.len;
+    }
+  else if (gdbpy_is_value_object (handle_obj))
+    {
+      struct value *val = value_object_to_value (handle_obj);
+      bytes = value_contents_all (val);
+      bytes_len = TYPE_LENGTH (value_type (val));
+    }
+  else
     {
       PyErr_SetString (PyExc_TypeError,
 		       _("Argument 'handle_obj' must be a thread handle object."));
@@ -781,9 +799,10 @@ infpy_thread_from_thread_handle (PyObject *self, PyObject *args, PyObject *kw)
   try
     {
       struct thread_info *thread_info;
-      struct value *val = value_object_to_value (handle_obj);
 
-      thread_info = find_thread_by_handle (val, inf_obj->inferior);
+      thread_info = find_thread_by_handle
+        (gdb::array_view<const gdb_byte> (bytes, bytes_len),
+	 inf_obj->inferior);
       if (thread_info != NULL)
 	return thread_to_thread_object (thread_info).release ();
     }

gdb/thread.c

@@ -540,11 +540,11 @@ find_thread_ptid (inferior *inf, ptid_t ptid)
 /* See gdbthread.h.  */
 
 struct thread_info *
-find_thread_by_handle (struct value *thread_handle, struct inferior *inf)
+find_thread_by_handle (gdb::array_view<const gdb_byte> handle,
+		       struct inferior *inf)
 {
-  return target_thread_handle_to_thread_info
+  return target_thread_handle_to_thread_info (handle.data (),
-	   (value_contents_all (thread_handle),
+					      handle.size (),
-	    TYPE_LENGTH (value_type (thread_handle)),
 					      inf);
 }