[Kimchi-devel] [PATCH v5 1/3] Use locks to prevent concurrent updates to VMs

[Aline Manera]

I will apply just this patch as the other 2 breaks the tests.

On 04/10/2015 19:37, Jose Ricardo Ziviani wrote:
> From: Crístian Deives <cristiandeives at gmail.com>
>
> If several users try to update the same VM at the same time, an error
> may happen due to concurrent access.
>
> Define a dictionary containing one lock per each VM, and use it when
> updating the VM: the lock is acquired before the update operation begins
> and it is released when the operation finishes (whether by success or
> failure).
>
> Signed-off-by: Crístian Deives <cristiandeives at gmail.com>
> Signed-off-by: Jose Ricardo Ziviani <joserz at linux.vnet.ibm.com>
> ---
>   src/wok/plugins/kimchi/model/vms.py | 18 ++++++++++++++----
>   1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/src/wok/plugins/kimchi/model/vms.py b/src/wok/plugins/kimchi/model/vms.py
> index d2dec90..a42e8af 100644
> --- a/src/wok/plugins/kimchi/model/vms.py
> +++ b/src/wok/plugins/kimchi/model/vms.py
> @@ -23,6 +23,7 @@ import lxml.etree as ET
>   import os
>   import random
>   import string
> +import threading
>   import time
>   import uuid
>   from lxml import etree, objectify
> @@ -79,6 +80,9 @@ XPATH_DOMAIN_UUID = '/domain/uuid'
>
>   XPATH_NUMA_CELL = './cpu/numa/cell'
>
> +# key: VM name; value: lock object
> +vm_locks = {}
> +
>
>   class VMsModel(object):
>       def __init__(self, **kargs):
> @@ -220,10 +224,16 @@ class VMModel(object):
>           self.stats = {}
>
>       def update(self, name, params):
> -        dom = self.get_vm(name, self.conn)
> -        vm_name, dom = self._static_vm_update(name, dom, params)
> -        self._live_vm_update(dom, params)
> -        return vm_name
> +        lock = vm_locks.get(name)
> +        if lock is None:
> +            lock = threading.Lock()
> +            vm_locks[name] = lock
> +
> +        with lock:
> +            dom = self.get_vm(name, self.conn)
> +            vm_name, dom = self._static_vm_update(name, dom, params)
> +            self._live_vm_update(dom, params)
> +            return vm_name
>
>       def clone(self, name):
>           """Clone a virtual machine based on an existing one.