Re: [RFA/commit] (Windows) remove thread notification for main thread of inferior

Joel Brobecker
2019-02-12T11:25:43Z

[-- Attachment #1: Type: text/plain, Size: 2806 bytes --]

Hi Simon,

> Hi Joel,
>
> I didn't test, but this looks good to me. Two small comments below.

Thanks for the review!

> > diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
> > index 2894b208f58..ae05d889a6a 100644
> > --- a/gdb/windows-nat.c
> > +++ b/gdb/windows-nat.c
> > @@ -426,9 +426,17 @@ thread_rec (DWORD id, int get_context)
> > return NULL;
> > }
> >
> > -/* Add a thread to the thread list. */
> > +/* Add a thread to the thread list.
> > +
> > + PTID is the ptid of the thread to be deleted.
> > + H is its Windows handle.
> > + TLB is its thread local base.
> > + MAIN_THREAD_P should be true if the thread to be deleted is
> > + the main thread, false otherwise. */
>
> This comment about the function that adds threads talks about things to be
> deleted.

Indeed. Fixed in the attached version.

> > static windows_thread_info *
> > -windows_add_thread (ptid_t ptid, HANDLE h, void *tlb)
> > +windows_add_thread (ptid_t ptid, HANDLE h, void *tlb,
> > + bool main_thread_p = false)
>
> Just a nit: in this case, where there are very few callers to update, I
> would opt for not using a default parameter value. It's probably just a
> personal preference, but I find it clearer to have the explicit value at the
> call site.

It wasn't really the number of callers to update that prompted me to
use a default value, but rather the fact that, in the normal case,
that parameter is really redundant, at least as far as the reader's
understanding is concerned. This is related a bit to the fact that
I am partial to the option of being able to name parameters at the
point call, something that C++ doesn't support. This would have been
particularly useful in this case here, because I've always found
"true" or "false" litteral constants in function calls like that
to be rather mysterious. So much so that I felt I needed to add
a comment to name them that way. Since it felt like providing it
at the point of call when false was redundant, I decided against
providing its value.

The attached patch follows your suggestion nonetheless. I worked
around my concern the same way I did when passing the new parameter
as true, and so this is good for me.

gdb/ChangeLog

* windows-nat.c (windows_add_thread): Add new parameter
"main_thread_p" with default value set to false. Update
function documentation as well as all callers.
(windows_delete_thread): Likewise.
(fake_create_process): Update call to windows_add_thread.
(get_windows_debug_event) <CREATE_THREAD_DEBUG_EVENT>
<CREATE_PROCESS_DEBUG_EVENT>: Likewise.
<EXIT_THREAD_DEBUG_EVENT, EXIT_PROCESS_DEBUG_EVENT>: Update
call to windows_delete_thread.

Tested on x86-windows (MinGW) using AdaCore's testsuite.
OK to push?

Thanks!
--
Joel

[-- Attachment #2: 0001-Windows-remove-thread-notification-for-main-thread-o.patch --]
[-- Type: text/x-diff, Size: 6818 bytes --]

From 83d8d40a71096c5138b5b41fc9ac365028d0b8c3 Mon Sep 17 00:00:00 2001
From: Joel Brobecker <brobecker@adacore.com>
Date: Tue, 12 Feb 2019 12:06:43 +0100
Subject: [PATCH] (Windows) remove thread notification for main thread of
inferior

This is a followup on a recent patch which, among other things
introduced the exit notification of the main thread in order
to be symetrical with the fact that a thread notification was
emitted before signaling its creation.

This patch takes the opposite approach of removing both creation
and exit notifications for that main thread, which is consistent
with what is done on other platforms such as GNU/Linux for instance.

gdb/ChangeLog

* windows-nat.c (windows_add_thread): Add new parameter
"main_thread_p" with default value set to false. Update
function documentation as well as all callers.
(windows_delete_thread): Likewise.
(fake_create_process): Update call to windows_add_thread.
(get_windows_debug_event) <CREATE_THREAD_DEBUG_EVENT>
<CREATE_PROCESS_DEBUG_EVENT>: Likewise.
<EXIT_THREAD_DEBUG_EVENT, EXIT_PROCESS_DEBUG_EVENT>: Update
call to windows_delete_thread.

Tested on x86-windows (MinGW) using AdaCore's testsuite.
---
gdb/windows-nat.c | 78 ++++++++++++++++++++++++++++++++++++++++---------------
1 file changed, 57 insertions(+), 21 deletions(-)

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 2894b20..f0fc8ec 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -426,9 +426,16 @@ thread_rec (DWORD id, int get_context)
return NULL;
}

-/* Add a thread to the thread list. */
+/* Add a thread to the thread list.
+
+ PTID is the ptid of the thread to be added.
+ H is its Windows handle.
+ TLB is its thread local base.
+ MAIN_THREAD_P should be true if the thread to be deleted is
+ the main thread, false otherwise. */
+
static windows_thread_info *
-windows_add_thread (ptid_t ptid, HANDLE h, void *tlb)
+windows_add_thread (ptid_t ptid, HANDLE h, void *tlb, bool main_thread_p)
{
windows_thread_info *th;
DWORD id;
@@ -446,7 +453,17 @@ windows_add_thread (ptid_t ptid, HANDLE h, void *tlb)
th->thread_local_base = (CORE_ADDR) (uintptr_t) tlb;
th->next = thread_head.next;
thread_head.next = th;
- add_thread (ptid);
+
+ /* Add this new thread to the list of threads.
+
+ To be consistent with what's done on other platforms, we add
+ the main thread silently (in reality, this thread is really
+ more of a process to the user than a thread). */
+ if (main_thread_p)
+ add_thread_silent (ptid);
+ else
+ add_thread (ptid);
+
/* Set the debug registers for the new thread if they are used. */
if (debug_registers_used)
{
@@ -483,9 +500,15 @@ windows_init_thread_list (void)
thread_head.next = NULL;
}

-/* Delete a thread from the list of threads. */
+/* Delete a thread from the list of threads.
+
+ PTID is the ptid of the thread to be deleted.
+ EXIT_CODE is the thread's exit code.
+ MAIN_THREAD_P should be true if the thread to be deleted is
+ the main thread, false otherwise. */
+
static void
-windows_delete_thread (ptid_t ptid, DWORD exit_code)
+windows_delete_thread (ptid_t ptid, DWORD exit_code, bool main_thread_p)
{
windows_thread_info *th;
DWORD id;
@@ -494,11 +517,19 @@ windows_delete_thread (ptid_t ptid, DWORD exit_code)

id = ptid.tid ();

+ /* Emit a notification about the thread being deleted.
+
+ Note that no notification was printed when the main thread
+ was created, and thus, unless in verbose mode, we should be
+ symetrical, and avoid that notification for the main thread
+ here as well. */
+
if (info_verbose)
printf_unfiltered ("[Deleting %s]\n", target_pid_to_str (ptid));
- else if (print_thread_events)
+ else if (print_thread_events && !main_thread_p)
printf_unfiltered (_("[%s exited with code %u]\n"),
target_pid_to_str (ptid), (unsigned) exit_code);
+
delete_thread (find_thread_ptid (ptid));

for (th = &thread_head;
@@ -1375,11 +1406,12 @@ fake_create_process (void)
/* We can not debug anything in that case. */
}
main_thread_id = current_event.dwThreadId;
- current_thread = windows_add_thread (
- ptid_t (current_event.dwProcessId, 0,
- current_event.dwThreadId),
- current_event.u.CreateThread.hThread,
- current_event.u.CreateThread.lpThreadLocalBase);
+ current_thread
+ = windows_add_thread (ptid_t (current_event.dwProcessId, 0,
+ current_event.dwThreadId),
+ current_event.u.CreateThread.hThread,
+ current_event.u.CreateThread.lpThreadLocalBase,
+ true /* main_thread_p */);
return main_thread_id;
}

@@ -1548,10 +1580,11 @@ get_windows_debug_event (struct target_ops *ops,
}
/* Record the existence of this thread. */
thread_id = current_event.dwThreadId;
- th = windows_add_thread (ptid_t (current_event.dwProcessId, 0,
- current_event.dwThreadId),
- current_event.u.CreateThread.hThread,
- current_event.u.CreateThread.lpThreadLocalBase);
+ th = windows_add_thread
+ (ptid_t (current_event.dwProcessId, 0, current_event.dwThreadId),
+ current_event.u.CreateThread.hThread,
+ current_event.u.CreateThread.lpThreadLocalBase,
+ false /* main_thread_p */);

break;

@@ -1562,7 +1595,8 @@ get_windows_debug_event (struct target_ops *ops,
"EXIT_THREAD_DEBUG_EVENT"));
windows_delete_thread (ptid_t (current_event.dwProcessId, 0,
current_event.dwThreadId),
- current_event.u.ExitThread.dwExitCode);
+ current_event.u.ExitThread.dwExitCode,
+ false /* main_thread_p */);
th = &dummy_thread_info;
break;

@@ -1578,10 +1612,12 @@ get_windows_debug_event (struct target_ops *ops,
current_process_handle = current_event.u.CreateProcessInfo.hProcess;
main_thread_id = current_event.dwThreadId;
/* Add the main thread. */
- th = windows_add_thread (ptid_t (current_event.dwProcessId, 0,
- current_event.dwThreadId),
- current_event.u.CreateProcessInfo.hThread,
- current_event.u.CreateProcessInfo.lpThreadLocalBase);
+ th = windows_add_thread
+ (ptid_t (current_event.dwProcessId, 0,
+ current_event.dwThreadId),
+ current_event.u.CreateProcessInfo.hThread,
+ current_event.u.CreateProcessInfo.lpThreadLocalBase,
+ true /* main_thread_p */);
thread_id = current_event.dwThreadId;
break;

@@ -1601,7 +1637,7 @@ get_windows_debug_event (struct target_ops *ops,
{
windows_delete_thread (ptid_t (current_event.dwProcessId, 0,
main_thread_id),
- 0);
+ 0, true /* main_thread_p */);
ourstatus->kind = TARGET_WAITKIND_EXITED;
ourstatus->value.integer = current_event.u.ExitProcess.dwExitCode;
thread_id = main_thread_id;
--
2.8.3