Following the discussion about an API to pin and unpin preset samples in the sample cache here:
https://lists.nongnu.org/archive/html/fluid-dev/2020-10/msg00016.html
Short explanation of the change:
Only the default loader currently supports dynamic sample loading, so I thought it might be a good idea to keep the changes for this feature mostly contained in the default loader as well. I've added two new preset notify flags (FLUID_PRESET_PIN and FLUID_PRESET_UNPIN) that are handled by the preset->notify callback and trigger the loading and possibly unloading of the samples.
Proposing a new event queue for the sequencer, based on prior discussion:
https://lists.nongnu.org/archive/html/fluid-dev/2019-12/msg00001.html
With this change fluidsynth will require a C++98 compliant compiler.
Consider this as RFC, feedback is welcome.
The "pain-points" from the discussion:
#### 1. It is slow.
Done (thanks to heap sort), see runtime of `test_seq_event_queue_sort`.
#### 2. A meaningful ordering for events with the same tick has not been considered.
Done, see comments in `fluid_seq_queue.cpp`.
#### 3. Complicated implementation
Now uses one single event queue, which requires C++98. Implemented similarly to std::priority_queue by using heap sort.
The "queue" I use currently is of type `std::deque`. `deque` does not provide preallocation. `std::vector` does provide it. However, `std::deque` has the huge advantage that appending additional elements is cheap. For `std::vector` appending new elements would require to reallocate all the memory and copy it to the new array. So,
* either use `std::deque` with the risk that memory allocation may occur during `fluid_sequencer_send_at()`, or
* use `std::vector` with a preallocated pool of events and make `fluid_sequencer_send_at()` when the `vector` runs out of capacity.
Comments?
#### 4. Events that have been processed are deleted and gone.
After having thought about this more, this is the correct behavior. After events have been dispatched, they must be released to free underlying memory, see point 3. For the very rare case that a client (e.g. fluid_player) may require those events in the future, the client should be responsible for storing the events somewhere.
#### 5. The sequencer supports the system timer as alternative time source.
The conclusion from the mailing list was that the system timer can be removed. This has been done.
#### 6. Time Scaling
Time scaling can now be used for arbitrary tempo changes. The previous implementation was capable of that as well, however, the time-scale was limited to 1000. The only limitation for the scale is now >0, see `test_seq_scale`.
### Other Points
* `fluid_sequencer_remove_events()` turned out to be broken before, as it did not remove all events from the queue. This has been fixed, see `test_seq_event_queue_remove`.
* Consider the following code executed by `threadA`:
```c
fluid_sequencer_send_at(event0);
fluid_sequencer_set_time_scale(); // new scale
fluid_sequencer_send_at(event1);
```
The new scale will be definitely applied to `event1`. However, if another concurrently running `threadB` executes `fluid_sequencer_process()`, it was previously not clear, whether the new scale was also applied to event0. This depends on whether `event0` was still in the `preQueue`, and this depends on `event0.time` and the tick count that `fluid_sequencer_process()` is being called with. This has been changed. As of now, events are queued with their timestamp AS-IS. And only the latest call to `fluid_sequencer_set_time_scale()` is being considered during `fluid_sequencer_process()`. This makes the implementation very simple, i.e. no events need to be changed and the sequencer doesn't have to be locked down. On the other hand, it means that `fluid_sequencer_set_time_scale()` can only be used for tempo changes when called from the sequencer callback. In other words, if `threadA` executes the code above followed by `fluid_sequencer_process()`, `event0` and `event1` will be executed with the same tempo, which is the latest scale provided to the seq. Is this acceptable? The old implementation had the same limitation. And when looking through the internet, I only find users who call `fluid_sequencer_set_time_scale()` from the sequencer callback. Still, this is a point I'm raising for discussion.
During the creation of a jack audio driver, it is checked whether the sample-rate of the settings object matches jack's rate. If not, it was adjusted previously via fluid_synth_set_sample_rate(). Due to the deprecation of that function and removal of real-time capability of the synth.sample-rate setting, a regression was introduced in 5fbddcecc3 causing the synth's sample-rate to be not updated.
This workaround obtains the synth via the settings instance and for now calls the deprecated sample-rate set function.
