Because callout functions execute asynchronously, it’s possible for a callout function to be called while another thread attempts to stop or reschedule it; thus creating a race condition. Fortunately, there are two simple solutions available for solving this problem:
callout_init_mtx
, callout_init_rw
, or callout_init(foo, 0)
Callout functions associated with a lock are exempt from the race condition described above—as long as the associated lock is held before calling the callout management functions.
callout_drain
to permanently cancel a callout functionUse callout_drain
instead of callout_stop
to permanently cancel a callout function. See, by waiting for the callout function to finish, you can’t destroy any objects that it might need.
We’ll walk through an example that uses callouts in Chapter 6.
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