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[PATCH 3/3] python/qemu/qmp.py: Fix settimeout operation
From: |
John Snow |
Subject: |
[PATCH 3/3] python/qemu/qmp.py: Fix settimeout operation |
Date: |
Fri, 9 Oct 2020 13:51:23 -0400 |
We enabled callers to interface directly with settimeout, but this
reacts poorly with blocking/nonblocking operation; as they are using the
same internal mechanism.
1. Whenever we change the blocking mechanism temporarily, always set it
back to what it was afterwards.
2. Disallow callers from setting a timeout of "0", which means
Non-blocking mode. This is going to create more weird problems than
anybody wants, so just forbid it.
I opt not to coerce '0' to 'None' to maintain the principal of least
surprise in mirroring the semantics of Python's interface.
Signed-off-by: John Snow <jsnow@redhat.com>
---
python/qemu/qmp.py | 23 +++++++++++++++++------
1 file changed, 17 insertions(+), 6 deletions(-)
diff --git a/python/qemu/qmp.py b/python/qemu/qmp.py
index 4969e5741cb..f64517fb0a7 100644
--- a/python/qemu/qmp.py
+++ b/python/qemu/qmp.py
@@ -164,16 +164,19 @@ def __get_events(self, wait: Union[bool, float] = False)
-> None:
retrieved or if some other error occurred.
"""
+ # Current timeout and blocking status
+ current_timeout = self.__sock.gettimeout()
+
# Check for new events regardless and pull them into the cache:
try:
- self.__sock.setblocking(False)
+ self.__sock.settimeout(0) # i.e. setblocking(False)
self.__json_read()
except OSError as err:
# EAGAIN: No data available; not critical
if err.errno != errno.EAGAIN:
raise
finally:
- self.__sock.setblocking(True)
+ self.__sock.settimeout(current_timeout)
# Wait for new events, if needed.
# if wait is 0.0, this means "no wait" and is also implicitly false.
@@ -187,9 +190,11 @@ def __get_events(self, wait: Union[bool, float] = False)
-> None:
except Exception as err:
msg = "Error while reading from socket"
raise QMPConnectError(msg) from err
+ finally:
+ self.__sock.settimeout(current_timeout)
+
if ret is None:
raise QMPConnectError("Error while reading from socket")
- self.__sock.settimeout(None)
def __enter__(self) -> 'QEMUMonitorProtocol':
# Implement context manager enter function.
@@ -219,7 +224,7 @@ def connect(self, negotiate: bool = True) ->
Optional[QMPMessage]:
return self.__negotiate_capabilities()
return None
- def accept(self, timeout: float = 15.0) -> QMPMessage:
+ def accept(self, timeout: Optional[float] = 15.0) -> QMPMessage:
"""
Await connection from QMP Monitor and perform capabilities negotiation.
@@ -338,13 +343,19 @@ def close(self) -> None:
if self.__sockfile:
self.__sockfile.close()
- def settimeout(self, timeout: float) -> None:
+ def settimeout(self, timeout: Optional[float]) -> None:
"""
Set the socket timeout.
- @param timeout (float): timeout in seconds, or None.
+ @param timeout (float): timeout in seconds (non-zero), or None.
@note This is a wrap around socket.settimeout
+
+ @raise ValueError: if timeout was set to 0.
"""
+ if timeout == 0:
+ msg = "timeout cannot be 0; this engages non-blocking mode."
+ msg += " Use 'None' instead to disable timeouts."
+ raise ValueError(msg)
self.__sock.settimeout(timeout)
def get_sock_fd(self) -> int:
--
2.26.2
- [PATCH 0/3] python/qemu: strictly typed mypy conversion, pt3, John Snow, 2020/10/09
- [PATCH 1/3] python: add mypy config, John Snow, 2020/10/09
- [PATCH 2/3] python/qemu/qmp.py: re-raise OSError when encountered, John Snow, 2020/10/09
- [PATCH 3/3] python/qemu/qmp.py: Fix settimeout operation,
John Snow <=
- Re: [PATCH 0/3] python/qemu: strictly typed mypy conversion, pt3, John Snow, 2020/10/09
- Re: [PATCH 0/3] python/qemu: strictly typed mypy conversion, pt3, John Snow, 2020/10/12