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Make sure multiple calls to _get_session() aren't nested

Fixes bug 924918

async_call_plugin() acquires a xenapi session as does the nested call to
get_xenapi_host(). This can cause a deadlock if multiple greenthreads
all block waiting for the outer sessions to be freed to allocate the
inner session. This change moves the call to get_xenapi_host() to outside
the with statement to ensure calls to _get_session() aren't nested.

Change-Id: I8f5490f40a9ccaf74a276187f66519a5d5f52b2e
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jerdfelt committed Feb 1, 2012
1 parent 8908d8b commit 093e4d38d511c7bb8d48fceebbfd8e350b533075
Showing with 5 additions and 1 deletion.
  1. +5 −1 nova/virt/xenapi_conn.py
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@@ -544,10 +544,14 @@ def call_xenapi_request(self, method, *args):
def async_call_plugin(self, plugin, fn, args):
"""Call Async.host.call_plugin on a background thread."""
# NOTE(johannes): Fetch host before we acquire a session. Since
# _get_session() acquires a session too, it can result in a deadlock
# if multiple greenthreads race with each other. See bug 924918
host = self.get_xenapi_host()
with self._get_session() as session:
return tpool.execute(self._unwrap_plugin_exceptions,
session.xenapi.Async.host.call_plugin,
self.get_xenapi_host(), plugin, fn, args)
host, plugin, fn, args)
def wait_for_task(self, task, uuid=None):
"""Return the result of the given task. The task is polled

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