From: Tom de Vries <tdevries@suse.de>
To: gdb-patches@sourceware.org
Cc: Pedro Alves <palves@redhat.com>, Simon Marchi <simon.marchi@polymtl.ca>
Subject: [RFC][gdb/doc] Document non-stop attach behaviour
Date: Mon, 7 Jun 2021 15:21:28 +0200 [thread overview]
Message-ID: <20210607132127.GA10588@delia.home> (raw)
Hi,
While investigating PR27908, I got confused about what the proper behaviour
is when attaching to a multi-threaded program in non-stop mode.
In particular, when running a script that issues an "info threads" after an
attach in non-stop mode, it can show a non-current thread as still running:
...
$ ./a.out & pid=$!; \
gdb -q \
-iex "set trace-commands on" \
-iex "set pagination off" \
-iex "set non-stop on" \
-p $pid \
-ex "info threads"
[2] 10038
+set pagination off
+set non-stop on
Attaching to process 10038
[New LWP 10040]
main () at test.c:37
37 while (1)
+info threads
Id Target Id Frame
* 1 Thread 0x7f63547a8740 (LWP 10038) "a.out" main () at t.c:37
2 Thread 0x7f6353fd7700 (LWP 10040) "a.out" (running)
(gdb)
Thread 2 "a.out" stopped.
thread_func (p=0x0) at test.c:13
13 while (1)
...
An "info threads" after the 'Thread 2 "a.out" stopped' message will show it as
stopped though:
...
info threads
+info threads
Id Target Id Frame
* 1 Thread 0x7f63547a8740 (LWP 10038) "a.out" main () at t.c:37
2 Thread 0x7f6353fd7700 (LWP 10040) "a.out" thread_func (p=0x0) at t.c:13
(gdb)
...
In conclusion, it seems that attaching in non-stop mode stops all threads,
just like in all-stop mode. But the stopping of non-current threads is
visible to the user.
Update the non-stop documentation to describe the attach behaviour in some
detail.
Any comments?
Thanks,
- Tom
[gdb/doc] Document non-stop attach behaviour
gdb/doc/ChangeLog:
2021-06-07 Tom de Vries <tdevries@suse.de>
* gdb.texinfo (Non-Stop Mode): Describe non-stop attach behaviour.
---
gdb/doc/gdb.texinfo | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index d09b86cda95..0fd7ab16150 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -6957,6 +6957,13 @@ one thread while allowing others to run freely, stepping
one thread while holding all others stopped, or stepping several threads
independently and simultaneously.
+Note that attaching in non-stop mode stops all threads, just as in
+all-stop mode. However, while in all-stop mode the attach command is
+finished only once all threads are stopped, in non-stop mode it's
+finished once the current thread is stopped. Consequently, it's
+briefly possible to observe non-current threads still running after an
+attach.
+
To enter non-stop mode, use this sequence of commands before you run
or attach to your program:
next reply other threads:[~2021-06-07 13:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-07 13:21 Tom de Vries [this message]
2021-08-24 11:10 ` [PING][RFC][gdb/doc] " Tom de Vries
2021-08-26 2:55 ` [RFC][gdb/doc] " Simon Marchi
2021-08-26 10:08 ` Tom de Vries
2021-08-26 12:46 ` Tom de Vries
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