I recently had a minor task involving changing an option - on one of our command line tools - from taking a required argument, to taking an optional argument. This should be easy they said; just change the respective option struct to take an optional argument, add a colon to the optstring, and get on with your life.
Well, it proved to be easier said than done. My initial expectation was that a solution similar to the one below should just work. And it does work, just not in the way I expected.
Introduction In the CFEngine Core team, we have recently been working on a fix for our WaitForCriticalSection() function. In short, the function checks a timestamp in a chunk of (lock) data stored in a local LMDB database and if the timestamp is too old, it writes a new chunk of (lock) data with the new timestamp. However, this used to be done in separate steps - read the data from the DB and close DB, check the data and potentially write the new data into the DB. So, there was a race condition because if multiple processes did the same steps at the same time, they could have read and checked the same timestamp value and then write their own data with their new timestamps one after another. On the high-level perspective that meant multiple processes could have entered the critical section at the same time.
