如何正确关闭和释放 ALSA 资源

Question

如何正确关闭和释放 ALSA（和硬件参数）资源？ 我发现了很多例子。都不同。都有memleak。

例如：

#include <stdio.h>
#include <unistd.h>
#include <alsa/asoundlib.h>

int
main()
{
    snd_pcm_t *dev;

    snd_pcm_open(&dev, "default", SND_PCM_STREAM_PLAYBACK, 0);
    snd_pcm_close(dev);

    return 0;
}

Valgrind 报告：

==19586== LEAK SUMMARY:
==19586==    definitely lost: 0 bytes in 0 blocks
==19586==    indirectly lost: 0 bytes in 0 blocks
==19586==      possibly lost: 65,525 bytes in 2,020 blocks
==19586==    still reachable: 298 bytes in 6 blocks
==19586==         suppressed: 0 bytes in 0 blocks
==19586== Reachable blocks (those to which a pointer was found) are not shown.
==19586== To see them, rerun with: --leak-check=full --show-reachable=yes
==19586== 
==19586== ERROR SUMMARY: 116 errors from 116 contexts (suppressed: 4 from 4)
--19586-- 
--19586-- used_suppression:      2 dl-hack3-cond-1
--19586-- used_suppression:      2 glibc-2.5.x-on-SUSE-10.2-(PPC)-2a
==19586== 
==19586== ERROR SUMMARY: 116 errors from 116 contexts (suppressed: 4 from 4)

更新：

没有 snd_pcm_close() 我们有来自 117 个上下文的 117 个错误)))

Answer 1

用 alsalib 1.1.4.1 测试了这个例子：

#include <stdio.h>
#include <unistd.h>
#include <alsa/asoundlib.h>

int main()
{
    snd_pcm_t *dev;

    snd_pcm_open(&dev, "default", SND_PCM_STREAM_PLAYBACK, 0);
    snd_pcm_close(dev);
    snd_config_update_free_global();

    return 0;
}

按照 Paolo 的建议添加 snd_config_update_free_global()，valgrind 会显示很多这样的警告：

4,320 bytes in 60 blocks are possibly lost in loss record 91 of 94

摘要显示可能丢失的块：

==499== LEAK SUMMARY:
==499==    definitely lost: 0 bytes in 0 blocks
==499==    indirectly lost: 0 bytes in 0 blocks
==499==      possibly lost: 43,011 bytes in 1,311 blocks
==499==    still reachable: 111,131 bytes in 128 blocks
==499==         suppressed: 0 bytes in 0 blocks
==499== Reachable blocks (those to which a pointer was found) are not shown.
==499== To see them, rerun with: --leak-check=full --show-leak-kinds=all

可以用它做什么？

Answer 2

如果您在 snd_pcm_close(handle) 之后调用 snd_config_update_free_global() 释放全局配置，您将不会获得泄漏；