nebraska: Make runtime files creation atomic
Users of nebraska look for the existence of the port and pid files and
then read their content. If they read the content after the file(s) are
created but before they are written into, then problems can occur. In
this CL we first create partial files and then move them into their
final locations atomically.
BUG=b:179329819
TEST=./nebraska.py --runtime-root /tmp --log-file stdout
Change-Id: I6bf5307b68017657451e912b5517e36988d33c8a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2681308
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Jae Hoon Kim <kimjae@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
diff --git a/nebraska/nebraska.py b/nebraska/nebraska.py
index 1a752b2..c12f023 100755
--- a/nebraska/nebraska.py
+++ b/nebraska/nebraska.py
@@ -928,12 +928,9 @@
"""
self.nebraska = nebraska
self._runtime_root = runtime_root
+ self._runtime_files = {}
self._port = port
- if self._runtime_root:
- self._port_file = os.path.join(self._runtime_root, 'port')
- self._pid_file = os.path.join(self._runtime_root, 'pid')
-
self._httpd = None
self._server_thread = None
self._created_runtime_root = False
@@ -1042,14 +1039,26 @@
self._port = self._httpd.server_port
if self._runtime_root:
+ self._runtime_files = {
+ os.path.join(self._runtime_root, 'port'): self._port,
+ os.path.join(self._runtime_root, 'pid'): os.getpid(),
+ }
+
try:
if not os.path.exists(self._runtime_root):
os.makedirs(self._runtime_root)
self._created_runtime_root = True
- with open(self._port_file, 'w') as port_file:
- port_file.write(str(self._port))
- with open(self._pid_file, 'w') as pid_file:
- pid_file.write(str(os.getpid()))
+ # Because the port and pid files might have been created but not written
+ # into, we create them in as temporary files and then move them to their
+ # final location so there won't be no race condition on the content of
+ # them.
+ for f, c in self._runtime_files.items():
+ with open(f + '.partial', 'w') as fp:
+ fp.write(str(c))
+
+ for f in self._runtime_files:
+ shutil.move(f + '.partial', f)
+
except IOError as err:
if err.errno == errno.EACCES:
print('Permission error: You need to run the script as root/sudo or '
@@ -1071,7 +1080,7 @@
if not self._runtime_root:
return
- for f in {self._port_file, self._pid_file}:
+ for f in self._runtime_files:
try:
os.remove(f)
except Exception as e:
