Fix race condition in reload_on_sighup functional

Race condition appears in next situation:

  1. First thread calls _set_config_value for one section.
  2. Second thread calls _set_config_value for another section.
  3. First thread. Config option value set, calls
     open(self.config_file, 'wb'), which erases all file content.
  4. Second thread. In previous point moment second thread tries to
     set config option value to self.config_file, which is empty (see 3).
     So, NoSectionError exception raised.

This patch adds ten retries for setting option value, if NoSectionError
raised, i.e. try to wait until self.config_file is busy.

Change-Id: Ic54ea287ebe4724511f75d42677cae5dfdec4e57
Closes-bug: #1535766

heat_integrationtests/common/config.py

@@ -130,6 +130,11 @@ IntegrationTestGroup = [
                default=30,
                help="Timeout in seconds to wait for adding or removing child"
                     "process after receiving of sighup signal"),
+    cfg.IntOpt('sighup_config_edit_retries',
+               default=10,
+               help='Count of retries to edit config file during sighup. If '
+                    'another worker already edit config file, file can be '
+                    'busy, so need to wait and try edit file again.'),
     cfg.StrOpt('heat-config-notify-script',
                default=('heat-config-notify'),
                help="Path to the script heat-config-notify"),

heat_integrationtests/functional/test_reload_on_sighup.py

@@ -28,8 +28,27 @@ class ReloadOnSighupTest(functional_base.FunctionalTestsBase):
 
     def _set_config_value(self, service, key, value):
         config = configparser.ConfigParser()
-        config.read(self.config_file)
+
-        config.set(service, key, value)
+        # NOTE(prazumovsky): If there are several workers, there can be
+        # situation, when one thread opens self.config_file for writing
+        # (so config_file erases with opening), in that moment other thread
+        # intercepts to this file and try to set config option value, i.e.
+        # write to file, which is already erased by first thread, so,
+        # NoSectionError raised. So, should wait until first thread writes to
+        # config_file.
+        retries_count = self.conf.sighup_config_edit_retries
+        while True:
+            config.read(self.config_file)
+            try:
+                config.set(service, key, value)
+            except configparser.NoSectionError:
+                if retries_count <= 0:
+                    raise
+                retries_count -= 1
+                eventlet.sleep(1)
+            else:
+                break
+
         with open(self.config_file, 'wb') as f:
             config.write(f)
 

heat_integrationtests/heat_integrationtests.conf.sample

@@ -112,5 +112,10 @@
 # receiving of sighup signal (integer value)
 #sighup_timeout = 30
 
+# Count of retries to edit config file during sighup. If another worker already
+# edit config file, file can be busy, so need to wait and try edit file
+# again. (integer value)
+#sighup_config_edit_retries = 10
+
 # Path to the script heat-config-notify (string value)
 #heat_config_notify_script = heat-config-notify