Re: [PATCH 4/5] python/qemu: qmp: Make QEMUMonitorProtocol a context manager

2020-01-29 Thread Wainer dos Santos Moschetta 



On 1/8/20 10:23 PM, John Snow wrote:


On 12/27/19 8:41 AM, Wainer dos Santos Moschetta wrote:

This implement the __enter__ and __exit__ functions on
QEMUMonitorProtocol class so that it can be used on 'with'
statement and the resources will be free up on block end:

with QEMUMonitorProtocol(socket_path) as qmp:
 qmp.connect()
 qmp.command('query-status')

Signed-off-by: Wainer dos Santos Moschetta 
---
  python/qemu/qmp.py | 15 +--
  1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/python/qemu/qmp.py b/python/qemu/qmp.py
index 914b8c6774..6d55f53595 100644
--- a/python/qemu/qmp.py
+++ b/python/qemu/qmp.py
@@ -139,6 +139,15 @@ class QEMUMonitorProtocol:
  raise QMPConnectError("Error while reading from socket")
  self.__sock.settimeout(None)
  
+def __enter__(self):

+# Implement context manager enter function.
+return self
+
+def __exit__(self, exc_type, exc_value, exc_traceback):
+# Implement context manager exit function.
+self.close()
+return False
+
  def connect(self, negotiate=True):
  """
  Connect to the QMP Monitor and perform capabilities negotiation.
@@ -259,8 +268,10 @@ class QEMUMonitorProtocol:
  """
  Close the socket and socket file.
  """
-self.__sock.close()
-self.__sockfile.close()
+if self.__sock:
+self.__sock.close()
+if self.__sockfile:
+self.__sockfile.close()

Not evident on cold read: does self.close() change self.__sock and
self.__sockfile such that they are false-ish?



Because self.__exit__() calls self.close() even when a runtime exception 
raises, there isn't any guarantee that self.__sockfile and self.__sock 
were initialized. That's the reason why I added those guards.





close() I suspect might need to actually unset the __sock and __sockfile
fields.


The QEMUMonitorProtocol object is designed to be disposed after close() 
being called. So I don't see any reason to unset those fields. Unless I 
am missing something here...


Thanks for the comments!

- Wainer



  
  def settimeout(self, timeout):

  """

Re: [PATCH 4/5] python/qemu: qmp: Make QEMUMonitorProtocol a context manager

2020-01-08 Thread John Snow 



On 12/27/19 8:41 AM, Wainer dos Santos Moschetta wrote:
> This implement the __enter__ and __exit__ functions on
> QEMUMonitorProtocol class so that it can be used on 'with'
> statement and the resources will be free up on block end:
> 
> with QEMUMonitorProtocol(socket_path) as qmp:
> qmp.connect()
> qmp.command('query-status')
> 
> Signed-off-by: Wainer dos Santos Moschetta 
> ---
>  python/qemu/qmp.py | 15 +--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/python/qemu/qmp.py b/python/qemu/qmp.py
> index 914b8c6774..6d55f53595 100644
> --- a/python/qemu/qmp.py
> +++ b/python/qemu/qmp.py
> @@ -139,6 +139,15 @@ class QEMUMonitorProtocol:
>  raise QMPConnectError("Error while reading from socket")
>  self.__sock.settimeout(None)
>  
> +def __enter__(self):
> +# Implement context manager enter function.
> +return self
> +
> +def __exit__(self, exc_type, exc_value, exc_traceback):
> +# Implement context manager exit function.
> +self.close()
> +return False
> +
>  def connect(self, negotiate=True):
>  """
>  Connect to the QMP Monitor and perform capabilities negotiation.
> @@ -259,8 +268,10 @@ class QEMUMonitorProtocol:
>  """
>  Close the socket and socket file.
>  """
> -self.__sock.close()
> -self.__sockfile.close()
> +if self.__sock:
> +self.__sock.close()
> +if self.__sockfile:
> +self.__sockfile.close()

Not evident on cold read: does self.close() change self.__sock and
self.__sockfile such that they are false-ish?

close() I suspect might need to actually unset the __sock and __sockfile
fields.

>  
>  def settimeout(self, timeout):
>  """
>

[PATCH 4/5] python/qemu: qmp: Make QEMUMonitorProtocol a context manager

2019-12-27 Thread Wainer dos Santos Moschetta 
This implement the __enter__ and __exit__ functions on
QEMUMonitorProtocol class so that it can be used on 'with'
statement and the resources will be free up on block end:

with QEMUMonitorProtocol(socket_path) as qmp:
qmp.connect()
qmp.command('query-status')

Signed-off-by: Wainer dos Santos Moschetta 
---
 python/qemu/qmp.py | 15 +--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/python/qemu/qmp.py b/python/qemu/qmp.py
index 914b8c6774..6d55f53595 100644
--- a/python/qemu/qmp.py
+++ b/python/qemu/qmp.py
@@ -139,6 +139,15 @@ class QEMUMonitorProtocol:
 raise QMPConnectError("Error while reading from socket")
 self.__sock.settimeout(None)
 
+def __enter__(self):
+# Implement context manager enter function.
+return self
+
+def __exit__(self, exc_type, exc_value, exc_traceback):
+# Implement context manager exit function.
+self.close()
+return False
+
 def connect(self, negotiate=True):
 """
 Connect to the QMP Monitor and perform capabilities negotiation.
@@ -259,8 +268,10 @@ class QEMUMonitorProtocol:
 """
 Close the socket and socket file.
 """
-self.__sock.close()
-self.__sockfile.close()
+if self.__sock:
+self.__sock.close()
+if self.__sockfile:
+self.__sockfile.close()
 
 def settimeout(self, timeout):
 """
-- 
2.23.0