fix "xm list hangs"

If a command hold domains_lock, "xm list" would hang for waiting for the
lock. Such as creating many VMs at a script (such as 20), command of "xm list" could hang for long time(10 mins). I think domains_lock here only protect update(). So, we shouldn't do update before command of "list" really get this lock, but xm do need show the domain's information quickly. In this patch, if command couldn't get the domains_lock after 20 times trying, "xm list" would show the information of VMs without update().

diff -r b9c541d9c138 tools/python/xen/xend/XendDomain.py
--- a/tools/python/xen/xend/XendDomain.py Tue Jun 15 13:27:14 2010
+0100
+++ b/tools/python/xen/xend/XendDomain.py Mon Jun 21 10:47:56 2010
+0800
@@ -824,10 +824,16 @@
if type(state) == int:
state = POWER_STATE_NAMES[state]
state = state.lower()
-

-        self.domains_lock.acquire()
+        resu = False
+        count = 0
+        while True:

+ resu = self.domains_lock.acquire(0)
+ if resu or count < 20:
+ break
+ count += 1
try:
- self._refresh(refresh_shutdown = False)
+ if resu:
+ self._refresh(refresh_shutdown = False)

             # active domains
             active_domains = self.domains.values()
@@ -846,7 +852,8 @@
                                   POWER_STATE_NAMES[x._stateGet()].lower()
== state,
                               active_domains + inactive_domains)
         finally:
-            self.domains_lock.release()
+            if resu:
+                self.domains_lock.release()

def list_sorted(self, state = DOM_STATE_RUNNING):

-James Song (Wei)

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