AudioStream: Add destructor. Enables dynamic creation and destruction.

[chipaudette]

There's been great work on dynamic creation and destruction of AudioConnection instances. But, one has not been able to dynamically destroy AudioStream instances. This pull request seeks to remove this limitation.

In my view, the primary issue preventing dynamic destruction of AudioStream instancs is that the user had no way of removing an AudioStream instance from the AudioStream update list. You could go ahead and delete your instance, but the update list would still try to use that stale pointer. That would cause the system to hang.

This pull request adds a destructor to AudioStream. Now, when an AudioStream instance is destroyed, it removes the instance from the AudioStream update list.

The user must still remember to close out all of the AudioConnections that use the destroyed AudioStream instance, but that's at least possible for the user to do. Without AudioStream having a destructor, there is no way for the user to remove the instance to the update list.

This pull request includes both Teensy3 and Teensy4. It has been tested on a Teensy 4.1 and a Teensy 3.6.

[h4yn0nnym0u5e]

This doesn't work - the inputQueue[] array is part of the derived class, and has already been destroyed by the time this code executes

[h4yn0nnym0u5e]

This doesn't work - the inputQueue[] array is part of the derived class, and has already been destroyed by the time this code executes

[chipaudette]

Thanks for pointing this out. It's been removed from this minimal pull request and replaced with a comment about the need for derived classes to release their inputQueues.

Since no existing AudioStream classes in the Teensy Audio library do this, the system will likely see an orphaning of AudioMemory block(s) with every destruction of an AudioStream instance from the Teensy Audio library. This is unfortunate and should be addressed through subsequent pull requests.

As a user of the Teensy Audio library, however, it is at least possible (within the rules of C++ and within my skillset) to modify my AudioStream derived classes to release their inputQueues. It is currently NOT possible to get my instances out of AudioStream's update list. I'm completely frozen out. So, I still request that we include this minimal destructor as it lets me move forward.

[A-Dunstan]

I think the list removal has a couple of errors:

• it only ever checks if next_update == this, so the stream pointed to by first_update can never be unlinked
• since any stream instance will only be in the list once, there should be a break statement to terminate the loop once it's found/unlinked

[chipaudette]

I believe that I have now addressed the last two bullets ("first_update" and "break"). All of the latest edits have been tested on Teensy 4.1 and Teensy 3.6.

[chipaudette]

I'm plugging for this Pull Request again. Presuming that one trusts Bjarne Stroustrup and Herb Sutter, their ISO C++ guidelines suggest that a base class destructor should be public and virtual (or protected and non-virtual).

https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c35-a-base-class-destructor-should-be-either-public-and-virtual-or-protected-and-non-virtual

AudioStream has no destructor (well, it has the default one), which means that it's not virtual. This pull request is giving AudioStream an explicit destructor and this pull request makes it virtual. This is in line with the ISO C++ guidance.

Any chance it could be accepted?