ganeshmurthy commented on code in PR #1567:
URL: https://github.com/apache/qpid-dispatch/pull/1567#discussion_r885650797
##########
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:
Minor suggestion -
Does `next_port = port + 1` need to be done if the file is empty.
```
# read old value
self.port_file.seek(0, os.SEEK_END)
if self.port_file.tell() != 0:
# file is not empty, read the old port and increment it to
get next possible available port.
self.port_file.seek(0)
port = int(self.port_file.read())
next_port = port + 1
else:
# file is empty, so just start with a randint between 20000
and 30000
port = random.randint(self.port_range[0], self.port_range[1])
```
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