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Fri, 17 Sep 2021 10:31:36 -0700 (PDT) X-Google-Smtp-Source: ABdhPJz9TC7lftrztoqu8CYVkb2csQWmU3Hf5hLm3I09TuyG4WYR+lAHldNAG/6LsvfswAhcC7LARS7Bej5nZ8I+Z38= X-Received: by 2002:a05:6830:310c:: with SMTP id b12mr7308493ots.252.1631899896081; Fri, 17 Sep 2021 10:31:36 -0700 (PDT) MIME-Version: 1.0 References: <20210917054047.2042843-1-jsnow@redhat.com> <20210917054047.2042843-5-jsnow@redhat.com> In-Reply-To: From: John Snow Date: Fri, 17 Sep 2021 13:31:25 -0400 Message-ID: Subject: Re: [PATCH 04/15] python/qmp: clear events on get_events() call To: Hanna Reitz Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jsnow@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/alternative; boundary="0000000000009d83da05cc344d1e" Received-SPF: pass client-ip=216.205.24.124; envelope-from=jsnow@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.392, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Vladimir Sementsov-Ogievskiy , Eduardo Habkost , qemu-block@nongnu.org, qemu-devel , Cleber Rosa Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --0000000000009d83da05cc344d1e Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, Sep 17, 2021 at 8:51 AM Hanna Reitz wrote: > On 17.09.21 07:40, John Snow wrote: > > All callers in the tree *already* clear the events after a call to > > get_events(). Do it automatically instead and update callsites to remov= e > > the manual clear call. > > > > These semantics are quite a bit easier to emulate with async QMP, and > > nobody appears to be abusing some emergent properties of what happens i= f > > you decide not to clear them, so let's dial down to the dumber, simpler > > thing. > > > > Specifically: callers of clear() right after a call to get_events() are > > more likely expressing their desire to not see any events they just > > retrieved, whereas callers of clear_events() not in relation to a recen= t > > call to pull_event/get_events are likely expressing their desire to > > simply drop *all* pending events straight onto the floor. In the sync > > world, this is safe enough; in the async world it's nearly impossible t= o > > promise that nothing happens between getting and clearing the > > events. > > > > Making the retrieval also clear the queue is vastly simpler. > > > > Signed-off-by: John Snow > > --- > > python/qemu/machine/machine.py | 1 - > > python/qemu/qmp/__init__.py | 4 +++- > > python/qemu/qmp/qmp_shell.py | 1 - > > 3 files changed, 3 insertions(+), 3 deletions(-) > > [...] > > > diff --git a/python/qemu/qmp/__init__.py b/python/qemu/qmp/__init__.py > > index 269516a79b..ba15668c25 100644 > > --- a/python/qemu/qmp/__init__.py > > +++ b/python/qemu/qmp/__init__.py > > @@ -374,7 +374,9 @@ def get_events(self, wait: bool =3D False) -> > List[QMPMessage]: > > @return The list of available QMP events. > > """ > > self.__get_events(wait) > > - return self.__events > > + events =3D self.__events > > + self.__events =3D [] > > + return events > > Maybe it=E2=80=99s worth updating the doc string that right now just says= =E2=80=9CGet a > list of available QMP events=E2=80=9D? > > Yes, that's an oversight on my part. I'm updating it to: "Get a list of available QMP events and clear the list of pending events." and adding your RB. (Also, perhaps renaming it to get_new_events, but that=E2=80=99s an even we= aker > suggestion.) > I tried to avoid churn in the iotests as much as I could manage, so I think I will leave this be for now. I have an impression that the number of cases where one might wish to see events that have already been witnessed is actually quite low, so I am not sure that it needs disambiguation from a case that is essentially never used. (I have certainly been wrong before, though.) > Anyway: > > Reviewed-by: Hanna Reitz > > ~ thankyou ~ --0000000000009d83da05cc344d1e Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


=
On Fri, Sep 17, 2021 at 8:51 AM Hanna= Reitz <hreitz@redhat.com> w= rote:
On 17.09.2= 1 07:40, John Snow wrote:
> All callers in the tree *already* clear the events after a call to
> get_events(). Do it automatically instead and update callsites to remo= ve
> the manual clear call.
>
> These semantics are quite a bit easier to emulate with async QMP, and<= br> > nobody appears to be abusing some emergent properties of what happens = if
> you decide not to clear them, so let's dial down to the dumber, si= mpler
> thing.
>
> Specifically: callers of clear() right after a call to get_events() ar= e
> more likely expressing their desire to not see any events they just > retrieved, whereas callers of clear_events() not in relation to a rece= nt
> call to pull_event/get_events are likely expressing their desire to > simply drop *all* pending events straight onto the floor. In the sync<= br> > world, this is safe enough; in the async world it's nearly impossi= ble to
> promise that nothing happens between getting and clearing the
> events.
>
> Making the retrieval also clear the queue is vastly simpler.
>
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>=C2=A0 =C2=A0python/qemu/machine/machine.py | 1 -
>=C2=A0 =C2=A0python/qemu/qmp/__init__.py=C2=A0 =C2=A0 | 4 +++-
>=C2=A0 =C2=A0python/qemu/qmp/qmp_shell.py=C2=A0 =C2=A0| 1 -
>=C2=A0 =C2=A03 files changed, 3 insertions(+), 3 deletions(-)

[...]

> diff --git a/python/qemu/qmp/__init__.py b/python/qemu/qmp/__init__.py=
> index 269516a79b..ba15668c25 100644
> --- a/python/qemu/qmp/__init__.py
> +++ b/python/qemu/qmp/__init__.py
> @@ -374,7 +374,9 @@ def get_events(self, wait: bool =3D False) -> L= ist[QMPMessage]:
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0@return The list of available = QMP events.
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0"""
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0self.__get_events(wait)
> -=C2=A0 =C2=A0 =C2=A0 =C2=A0 return self.__events
> +=C2=A0 =C2=A0 =C2=A0 =C2=A0 events =3D self.__events
> +=C2=A0 =C2=A0 =C2=A0 =C2=A0 self.__events =3D []
> +=C2=A0 =C2=A0 =C2=A0 =C2=A0 return events

Maybe it=E2=80=99s worth updating the doc string that right now just says = =E2=80=9CGet a
list of available QMP events=E2=80=9D?


Yes, that's an oversight on my par= t. I'm updating it to:
"Get a list of available QMP even= ts and clear the list of pending events." and adding your RB.

(Also, perhaps renaming it to get_new_events, but that=E2=80=99s an even we= aker
suggestion.)

I tried to avoid churn in = the iotests as much as I could manage, so I think I will leave this be for = now. I have an impression that the number of cases where one might wish to = see events that have already been witnessed is actually quite low, so I am = not sure that it needs disambiguation from a case that is essentially never= used. (I have certainly been wrong before, though.)
=C2=A0
Anyway:

Reviewed-by: Hanna Reitz <hreitz@redhat.com>


~ thankyou ~

--0000000000009d83da05cc344d1e--