Memory leak alsa::pcm::PCM::open

[druskus20]

I first found out this issue working with cpal. (RustAudio/cpal#928)

I've reproduced this issue with this repo's pcm_record example. (I slightly modified it to make it not infinitely loop).

fn read_loop(pcm: &PCM) -> Result<(), Error> {
    let io = pcm.io_i16()?;
    let mut buf = [0i16; 8192];
    for i in 0..10 {
        // Block while waiting for 8192 samples to be read from the device.
        assert_eq!(io.readi(&mut buf)?, buf.len());
        let r = rms(&buf);
        println!("RMS: {:.1} dB", r);
    }
    Ok(())
}

Running:

 valgrind -s --leak-check=full --show-leak-kinds=all ./target/debug/examples/pcm_record

Shows:

==1331522== 16,616 bytes in 1 blocks are still reachable in loss record 149 of 149
==1331522==    at 0x484D953: calloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==1331522==    by 0x5159CE8: ??? (in /usr/lib/x86_64-linux-gnu/libpipewire-0.3.so.0.1005.0)
==1331522==    by 0x5174096: ??? (in /usr/lib/x86_64-linux-gnu/libpipewire-0.3.so.0.1005.0)
==1331522==    by 0x515A818: pw_init (in /usr/lib/x86_64-linux-gnu/libpipewire-0.3.so.0.1005.0)
==1331522==    by 0x50BA67B: _snd_pcm_pipewire_open (in /usr/lib/x86_64-linux-gnu/alsa-lib/libasound_module_pcm_pipewire.so)
==1331522==    by 0x48CB6CD: ??? (in /usr/lib/x86_64-linux-gnu/libasound.so.2.0.0)
==1331522==    by 0x48CBD6D: ??? (in /usr/lib/x86_64-linux-gnu/libasound.so.2.0.0)
==1331522==    by 0x48FB37E: snd_pcm_open (in /usr/lib/x86_64-linux-gnu/libasound.so.2.0.0)
==1331522==    by 0x122614: alsa::pcm::PCM::open (error.rs:21)
==1331522==    by 0x122510: alsa::pcm::PCM::new (pcm.rs:147)
==1331522==    by 0x120AAC: pcm_record::start_capture (pcm_record.rs:7)
==1331522==    by 0x12181C: pcm_record::main (pcm_record.rs:50)

This is similar to:

jarikomppa/soloud#278