dumpsys用来dump某系统组件的信息：
*./frameworks/av/native/cmds/dumpsys/dumpsys.cpp*
```
sp<IServiceManager> sm = defaultServiceManager();
//...
for (size_t i=0; i<N; i++) {
sp<IBinder> service = sm->checkService(services[i]);
if (service != NULL) {
//...
int err = service->dump(STDOUT_FILENO, args);
}
}
```
从上面实现代码得知，dumpsys特指dump注册在ServiceManager里的`Service`, 每个`Service`都可以通过实现`dump`接口来说明自己的信息
以media.player为例：
*./frameworks/av/media/mediaserver/main_mediaserver.cpp*
```
int main(int argc, char** argv) {
MediaPlayerService::instatiate();
}
```
*./frameworks/av/media/libmediaplayerservice/MediaPlayerService.cpp*
```
void MediaPlayerService::instantiate() {
defaultServiceManager()->addService(
String16("media.player"), new MediaPlayerService());
}
```
mediaserver进程在ServiceManager里注册了`Service`，名字叫做"media.player"，最终dump实现：
```
status_t MediaPlayerService::Client::dump(...) const {
String8 result;
result.append(" Client\n");
snprintf(buffer, 255, " pid(%d), connId(%d), status(%d), looping(%s)\n",
mPid, mConnId, mStatus, mLoop?"true": "false");
result.append(buffer);
write(fd, result.string(), result.size());
if (mPlayer != NULL) {
mPlayer->dump(fd, args);
}
if (mAudioOutput != 0) {
mAudioOutput->dump(fd, args);
}
write(fd, "\n", 1);
}
```
当有视频播放的时候，敲入`dumpsys media.player`命令，可以输出：
``` ? ~ adb shell dumpsys media.player Client pid(17882), connId(5), status(0), looping(false) AwesomePlayer URI(suppressed), flags(0x00000008) Track 1 MIME(video/avc) videoDimensions(-1 x -1), numVideoFramesDecoded(0), numVideoFramesDropped(0) Track 2 MIME(audio/mp4a-latm) AudioOutput stream type(3), left - right volume(1.000000, 1.000000) msec per frame(0.000000), latency (-1) aux effect id(0), send level (0.000000) No media recorder client Files opened and/or mapped: ```
扩展阅读:
原文：http://my.oschina.net/caohong/blog/294633