RFR: 8301846: Invalid TargetDataLine after screen lock when using JFileChooser or COM library [v3]

[Alexey Ivanov]

On Wed, 26 Jul 2023 20:56:15 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

> > Probably… But it is still incorrect. Initialising COM on a thread doesn't mean you can call COM object methods from any thread in your application.
> 
> Note that "Objects created on a COM thread in a multithread apartment (MTA) must be able to receive method calls from other threads at any time", so if we initialisethe devices on one thread using COM they will be avaliable on other threads as well.

But from the threads where you initialised COM as MTA.

The docs for `CoInitializeEx` clearly state you have to initialise COM before you can use it. Thus, calling methods of COM objects from an arbitrary thread in your application is wrong, isn't it?

> But the spec for DirectSoundEnumerate says nothing about COM... But from some examples I see ppl wrap it by the CoInitializeEx(NULL, COINIT_MULTITHREADED)/CoUninitialize();
> 
> Noe sure we can call CoInitializeEx on the main thread.

It's for any thread not only the main thread… You can all `AudioSystem.getMixerInfo` from any thread in a Java app, if `DirectSoundEnumerate` needs COM to be initialised even though the documentation doesn't mention it, we have to initalise COM. Thus there are two options:

1. Call `CoInitializeEx`, enumerate devices, and call `CoUninitialize`.
2. Create an executor service which initialises COM on its worker thread, enumerate devices on the worker thread and return the devices. The worker thread may terminate (after it calls `CoUninitialize`) if it doesn't receive more requests in a period of time.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14898#discussion_r1275489954