From c722716736c94261de77b337f1bffe924b8724e3 Mon Sep 17 00:00:00 2001
From: Tim Laszlo <tim.laszlo@gmail.com>
Date: Fri, 26 Oct 2012 15:23:48 -0500
Subject: Probes/DatabaseBackend: add a thread lock for databases that cannot
 handle multiple writes

---
 src/lib/Bcfg2/Server/Core.py           |  3 +++
 src/lib/Bcfg2/Server/Plugin/helpers.py | 29 +++++++++++++++++++++++++++++
 src/lib/Bcfg2/Server/Plugins/Probes.py |  1 +
 3 files changed, 33 insertions(+)

(limited to 'src/lib')

diff --git a/src/lib/Bcfg2/Server/Core.py b/src/lib/Bcfg2/Server/Core.py
index 66a1a23a7..dca169b54 100644
--- a/src/lib/Bcfg2/Server/Core.py
+++ b/src/lib/Bcfg2/Server/Core.py
@@ -170,6 +170,9 @@ class BaseCore(object):
         #: :attr:`fam_thread`) to shutdown
         self.terminate = threading.Event()
 
+        #: RLock to be held on writes to the backend db
+        self.db_write_lock = threading.RLock()
+
         # generate Django ORM settings.  this must be done _before_ we
         # load plugins
         Bcfg2.settings.read_config(repo=self.datastore)
diff --git a/src/lib/Bcfg2/Server/Plugin/helpers.py b/src/lib/Bcfg2/Server/Plugin/helpers.py
index bbceb1989..c7798b705 100644
--- a/src/lib/Bcfg2/Server/Plugin/helpers.py
+++ b/src/lib/Bcfg2/Server/Plugin/helpers.py
@@ -118,6 +118,7 @@ class DatabaseBacked(Plugin):
     database.
 
     .. private-include: _use_db
+    .. private-include: _must_lock
     """
 
     #: The option to look up in :attr:`section` to determine whether or
@@ -148,6 +149,34 @@ class DatabaseBacked(Plugin):
             self.logger.error("%s is true but django not found" % self.option)
             return False
 
+    @property
+    def _must_lock(self):
+        """ Whether or not the backend database allows multiple
+        threads to write. """
+        engine = self.core.setup.cfp.get(Bcfg2.Options.DB_ENGINE.cf[0],
+                                         Bcfg2.Options.DB_ENGINE.cf[1],
+                                         default=Bcfg2.Options.DB_ENGINE.default)
+        if engine == 'sqlite3':
+            return True
+        else:
+            return False
+
+    @staticmethod
+    def _db_writer(fn):
+        """ Decorator to be used when a call will update the data
+        threads to write. """
+        def _acquire_and_run(self, *args, **kwargs):
+            if self._must_lock:
+                try:
+                    self.core.db_write_lock.acquire()
+                    rv = fn(self, *args, **kwargs)
+                finally:
+                    self.core.db_write_lock.release()
+            else:
+                rv = fn(self, *args, **kwargs)
+            return rv
+        return _acquire_and_run
+
 
 class PluginDatabaseModel(object):
     """ A database model mixin that all database models used by
diff --git a/src/lib/Bcfg2/Server/Plugins/Probes.py b/src/lib/Bcfg2/Server/Plugins/Probes.py
index bb1cbf81c..78dd2af85 100644
--- a/src/lib/Bcfg2/Server/Plugins/Probes.py
+++ b/src/lib/Bcfg2/Server/Plugins/Probes.py
@@ -218,6 +218,7 @@ class Probes(Bcfg2.Server.Plugin.Probing,
             err = sys.exc_info()[1]
             self.logger.error("Failed to write probed.xml: %s" % err)
 
+    @Bcfg2.Server.Plugin.DatabaseBacked._db_writer
     def _write_data_db(self, client):
         """ Write received probe data to the database """
         for probe, data in self.probedata[client.hostname].items():
-- 
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