Garbarge collector eats gdb.selected_thread().inferior

[Simon Marchi]

Hi Maksim,

The fix looks right, and Tom also said so in Bugzilla.

However, I'm unable to apply your patch to look at the test case.  The 
long lines have been wrapped, presumably by your email client.  Can you 
send it again using the "git send-email" command?  I'll still make the 
comments I can about the current version.

On 2017-08-05 07:57, Максим Дзабраев wrote:
> If multiple time call gdb.selected_thread ().inferior, gdb throw 
> exception:
> 
> (gdb) pi gdb.selected_thread().inferior
> <gdb.Inferior object at 0x7f1952bea698>
> (gdb) pi gdb.selected_thread().inferior
> <gdb.Inferior object at 0x7f1952bea698>
> (gdb) pi gdb.selected_thread().inferior
> Python Exception <type 'exceptions.AttributeError'> 'NoneType' object
> has no attribute 'inferior':
> Error while executing Python code.
> (gdb) info threads
>   Id   Target Id         Frame
> * 1    Thread 0x7f54f0474740 (LWP 584) "mc" 0x00007f54ef055c33 in
> select () from /lib/x86_64-linux-gnu/libc.so.6
> 
> I report about this bug here:
> https://sourceware.org/bugzilla/show_bug.cgi?id=21213
> 
> Following patch fixes this bug and add test of this bug. In attachment
> I add gdb.log and gdb.sum before and after apply patch to
> thpy_get_inferior.
> 
> 
> ChangeLog
> 2017.08.05 Maksim Dzabraev <dzabraew@gmail.com>
> 
>         * gdb/python/py-infthread.c (hpy_get_inferior)
>         * gdb/testsuite/gdb.python/py-infthread.exp: Fix bug 21213 and 
> add test

Please consult this page for details about the ChangeLog entries.

https://sourceware.org/gdb/wiki/ContributionChecklist

In short, each change should be documented in the ChangeLog closest to 
it (then for each file you write the relative path to it), and should 
describe what changed a bit more precisely.  For example:

gdb/ChangeLog:

	* python/py-infthread.c (thpy_get_inferior): Increment reference
	of inferior before returning it.

gdb/testsuite/ChangeLog:

	* gdb.python/py-infthread.exp: Test calling
	InferiorThread.inferior () multiple times in a row.

> ---
> 
> diff --git a/gdb/python/py-infthread.c b/gdb/python/py-infthread.c
> index 626c15c..31d576f 100644
> --- a/gdb/python/py-infthread.c
> +++ b/gdb/python/py-infthread.c
> @@ -162,6 +162,7 @@ thpy_get_inferior (PyObject *self, void *ignore)
>    thread_object *thread_obj = (thread_object *) self;
> 
>    THPY_REQUIRE_VALID (thread_obj);
> +  Py_INCREF (thread_obj->inf_obj);
> 
>    return thread_obj->inf_obj;
>  }
> diff --git a/gdb/testsuite/gdb.python/py-infthread.exp
> b/gdb/testsuite/gdb.python/py-infthread.exp
> index a5fed8d..dcb7e26 100644
> --- a/gdb/testsuite/gdb.python/py-infthread.exp
> +++ b/gdb/testsuite/gdb.python/py-infthread.exp
> @@ -39,6 +39,14 @@ if ![runto_main] then {
> 
>  # Test basic gdb.Inferior attributes and methods.
> 
> +#testing https://sourceware.org/bugzilla/show_bug.cgi?id=21213

It's nice to give a bit of context so that readers don't have to visit 
the PR to have an idea of what it's about.  I suggest:

# Make sure that InferiorThread.inferior returns a new reference (see PR 
21213).

> +gdb_py_test_silent_cmd "python gdb.selected_thread ().inferior" "test
> gdb.selected_thread" 1
> +gdb_py_test_silent_cmd "python gdb.selected_thread ().inferior" "test
> gdb.selected_thread" 1
> +gdb_test_no_output "python import gc; gc.collect()" "test
> InferiorThread.inferior" "test InferiorThread.inferior"

You have one too many parameter to gdb_test_no_output.  Also, the test 
name should probably be something like "call Python garbage collection".

> +gdb_py_test_silent_cmd "python gdb.selected_thread ().inferior" "test
> gdb.selected_thread" 1
> +gdb_py_test_silent_cmd "python gdb.selected_thread ().inferior" "test
> gdb.selected_thread" 1

All tests (here one line == one test) should have a unique name, so you 
could name them "test InferiorThread.inferior #" where # is 1, 2, 3, 4.

> +
> +
>  gdb_py_test_silent_cmd "python t0 = gdb.selected_thread ()" "test
> gdb.selected_thread" 1
>  gdb_test "python print (t0)" "\\<gdb.InferiorThread object at
> 0x\[\[:xdigit:\]\]+>" "verify InferiorThread object"
>  gdb_test "python print ('result = %s' % t0.num)" " = 1" "test

Thanks!

Simon