drm/output: Allow DrmOutput destruction during manager-lock
#1820
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Since #1778 we provide an api to explicitly lock the `DrmOutputManager` to apply multiple changes atomically without `DrmOutput`s being able to observe any inconsistent state. However as a side-effect of this, it has become impossible to re-assign a crtc to a different connector in one atomic opertion, as the lock on the `DrmOutputManager` prevents the `Drop`-implementation of `DrmOutput` to free any crtcs for re-use. This commit introduces a channel, if locking fails to deferr freeing the crtc to the locked manager.
Drakulix
changed the title
DrmOutput descruction during manager-lockDrmOutput destruction during manager-lock
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Since #1778 we provide an api to explicitly lock the
DrmOutputManagerto apply multiple changes atomically withoutDrmOutputs being able to observe any inconsistent state.However as a side-effect of this, it has become impossible to re-assign a crtc to a different connector in one atomic opertion, as the lock on the
DrmOutputManagerprevents theDrop-implementation ofDrmOutputto free any crtcs for re-use. This is a problem in cosmic-comp currently, when trying to apply a new configuration in one go on more resource constraint systems leading to a rejection of the entire configuration.This commit introduces a channel to defer freeing the crtc to the locked manager, if locking fails. Since this can be racy, we rely on the event-loop to free up any crtcs stuck in said channel. Synchronization with different threads for dropping the
DrmOutputstill needs to be handled by downstream (e.g. by joining said thread).I'd like to get some feedback on this approach. I also tried to fix this issue without involving the event-loop by using additional
CondVars and other synchronization primitives, but that grew very complex to the point where we might as well build our ownRwLockfor this specific purpose.