Re: [Qemu-devel] [PATCH 1/2] QMP: add get_events(wait=True) option

[Stefan Hajnoczi <stefanha@gmail.com>]

On Wed, May 25, 2011 at 10:15 PM, Luiz Capitulino
<lcapitulino@redhat.com> wrote:
> On Wed, 25 May 2011 19:48:00 +0100
> Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> wrote:
>
>> The get_events() function polls for new QMP events and then returns.  It
>> can be useful to wait for the next QMP event so add the boolean 'wait'
>> keyword argument.
>>
>> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
>> ---
>>  QMP/qmp.py |   11 ++++++++---
>>  1 files changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/QMP/qmp.py b/QMP/qmp.py
>> index 14ce8b0..2565508 100644
>> --- a/QMP/qmp.py
>> +++ b/QMP/qmp.py
>> @@ -43,7 +43,7 @@ class QEMUMonitorProtocol:
>>              family = socket.AF_UNIX
>>          return socket.socket(family, socket.SOCK_STREAM)
>>
>> -    def __json_read(self):
>> +    def __json_read(self, only_event=False):
>>          while True:
>>              data = self.__sockfile.readline()
>>              if not data:
>> @@ -51,7 +51,8 @@ class QEMUMonitorProtocol:
>>              resp = json.loads(data)
>>              if 'event' in resp:
>>                  self.__events.append(resp)
>> -                continue
>> +                if not only_event:
>> +                    continue
>>              return resp
>>
>>      error = socket.error
>> @@ -106,9 +107,11 @@ class QEMUMonitorProtocol:
>>              qmp_cmd['id'] = id
>>          return self.cmd_obj(qmp_cmd)
>>
>> -    def get_events(self):
>> +    def get_events(self, wait=False):
>>          """
>>          Get a list of available QMP events.
>> +
>> +        @param wait: block until an event is available (bool)
>>          """
>>          self.__sock.setblocking(0)
>>          try:
>> @@ -118,6 +121,8 @@ class QEMUMonitorProtocol:
>>                  # No data available
>>                  pass
>>          self.__sock.setblocking(1)
>> +        if not self.__events and wait:
>> +            self.__json_read(only_event=True)
>>          return self.__events
>
> Maybe this is better (untested):

I've tested it because that's how I implemented it first too :).
However, I don't want to block until the QMP monitor sends the next
event when there is already a received event pending.

The patch I posted polls for new events first, then only blocks if
there are no events available.

Stefan