ALSA control core allows applications to lock/unlock a control element so that any write opreation to the control element fails for processes except for owner process. When a process requests `SNDRV_CTL_IOCTL_ELEM_LOCK`[1] against a control element. After operating the request, the control element is under 'owned by the process' state. In this state, any request of `SNDRV_CTL_IOCTL_ELEM_WRITE` from the other processes fails with `-EPERM`[2]. The write operation from the owner process is successful only. When the owner process is going to finish, the state is released[3]. ALSA userspace library, a.k.a alsa-lib, has a pair of `snd_ctl_elem_lock()` and `snd_ctl_elem_unlock()` as its exported API[4].
Thank you Sakamoto-san for this explanation, I wasn't even aware this existed.
What I was trying to describe in my earlier answer is a different need to have an atomic update of *multiple* controls.
If e.g. a DSP or hardware engine exposes two separate filters for left and right channels, and the coefficients for those filters are modified with separate controls, it would be really nice to have the capability of writing these controls separately, but have a 'commit' mechanism so that these updated coefficients are used at the same time by the left and right filters.
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