Drop in-memory copy of schema zip file

The schema cache used a BytesIO buffer to read/write schema cache before
it got flushed to disk. Since the schema cache is now loaded in one go,
the temporary buffer is no longer needed.

File locking has been replaced with a temporary file and atomic rename.

Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: David Kupka <dkupka@redhat.com>

ipaclient/remote_plugins/schema.py

@@ -3,13 +3,11 @@
 #
 
 import collections
-import contextlib
 import errno
-import fcntl
-import io
 import json
 import os
 import sys
+import tempfile
 import types
 import zipfile
 
@@ -374,7 +372,6 @@ class Schema(object):
         self._dict = {}
         self._namespaces = {}
         self._help = None
-        self._file = six.BytesIO()
 
         for ns in self.namespaces:
             self._dict[ns] = {}
@@ -404,21 +401,6 @@ class Schema(object):
         self.fingerprint = fingerprint
         self.ttl = ttl
 
-    @contextlib.contextmanager
-    def _open(self, filename, mode):
-        path = os.path.join(self._DIR, filename)
-
-        with io.open(path, mode) as f:
-            if mode.startswith('r'):
-                fcntl.flock(f, fcntl.LOCK_SH)
-            else:
-                fcntl.flock(f, fcntl.LOCK_EX)
-
-            try:
-                yield f
-            finally:
-                fcntl.flock(f, fcntl.LOCK_UN)
-
     def _fetch(self, client, ignore_cache=False):
         if not client.isconnected():
             client.connect(verbose=False)
@@ -454,13 +436,10 @@ class Schema(object):
         return (fp, ttl,)
 
     def _read_schema(self, fingerprint):
-        self._file.truncate(0)
-        with self._open(fingerprint, 'rb') as f:
-            self._file.write(f.read())
-
         # It's more efficient to read zip file members at once than to open
         # the zip file a couple of times, see #6690.
-        with zipfile.ZipFile(self._file, 'r') as schema:
+        filename = os.path.join(self._DIR, fingerprint)
+        with zipfile.ZipFile(filename, 'r') as schema:
             for name in schema.namelist():
                 ns, _slash, key = name.partition('/')
                 if ns in self.namespaces:
@@ -502,8 +481,21 @@ class Schema(object):
             if e.errno != errno.EEXIST:
                 raise
 
-        self._file.truncate(0)
-        with zipfile.ZipFile(self._file, 'w', zipfile.ZIP_DEFLATED) as schema:
+        with tempfile.NamedTemporaryFile('wb', prefix=fingerprint,
+                                         dir=self._DIR, delete=False) as f:
+            try:
+                self._write_schema_data(f)
+                f.flush()
+                os.fdatasync(f.fileno())
+                f.close()
+            except Exception:
+                os.unlink(f.name)
+                raise
+            else:
+                os.rename(f.name, os.path.join(self._DIR, fingerprint))
+
+    def _write_schema_data(self, fileobj):
+        with zipfile.ZipFile(fileobj, 'w', zipfile.ZIP_DEFLATED) as schema:
             for key, value in self._dict.items():
                 if key in self.namespaces:
                     ns = value
@@ -519,11 +511,6 @@ class Schema(object):
                 json.dumps(self._generate_help(self._dict)).encode('utf-8')
             )
 
-        self._file.seek(0)
-        with self._open(fingerprint, 'wb') as f:
-            f.truncate(0)
-            f.write(self._file.read())
-
     def read_namespace_member(self, namespace, member):
         value = self._dict[namespace][member]