jiridanek commented on code in PR #1567:
URL: https://github.com/apache/qpid-dispatch/pull/1567#discussion_r885686638
##########
tests/system_test.py:
##########
@@ -765,6 +772,46 @@ def setup(self):
os.makedirs(self.directory)
os.chdir(self.directory)
+ def _next_port(self) -> int:
+ """Reads and increments value stored in self.port_file, under an
exclusive file lock.
+
+ When a lock cannot be acquired immediately, fcntl.lockf blocks.
+
+ Failure possibilities:
+ File locks may not work correctly on network filesystems. We still
should be no worse off than we were.
+
+ This method always unlocks the lock file, so it should not ever
deadlock other tests running in parallel.
+ Even if that happened, the lock is unlocked by the OS when the
file is closed, which happens automatically
+ when the process that opened and locked it ends.
+
+ Invalid content in the self.port_file will break this method.
Manual intervention is then required.
+ """
+ try:
+ fcntl.flock(self.port_file, fcntl.LOCK_EX)
+
+ # read old value
Review Comment:
In the beginning (no file), I return the result of random.randint and then
store port + 1 to file. Next time, I read number from file (to return) and
store number + 1 back to file and so on.
If I did not do port + 1 the first time, then I'd return the same port twice.
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