KERNEL: Simplify the ST-thread as simple object.

[winlinvip]

To keep object simple and no-reusable, read #786 or #288.
To simplify the thread model, read #902

[winlinvip]

The first category of thread, which has its inside loop, like the SrsSignalManager, it should be writen like:

class TestThread : public ISrsCoroutineHandler
{
public:
    SrsCoroutine trd;
public:
    TestThread() : trd("test",this) {
    }
    virtual ~TestThread() {
    }
public:
    int cycle() {
        while (!trd.pull()) {
            st_sleep(3); // Do something.
        }
        return ERROR_SUCCESS;
    }
};

Another type of thread, is need to be restart, like the SrsTcpListener, we must delete the thread then restart:

class SrsTcpListener : public ISrsCoroutineHandler
{
private:
    SrsCoroutine* trd;
public:
    SrsTcpListener() {
        trd = NULL;
    }
    virtual ~SrsTcpListener() {
        srs_freep(trd);
    }
public:
    virtual int start() {
        srs_freep(trd);
        trd = new SrsCoroutine("tcp", this);
        return trd->start();
    }
    virtual void stop() {
        trd->stop();
    }
    virtual int cycle() {
        while (!trd->pull()) {
            int fd = st_accept(xxx); // Accept and process fd.
        }
    }

It's important to check the thread is running then sleep, for example:

// when error, encoder sleep for a while and retry.
#define SRS_RTMP_ENCODER_CIMS (3000)

int SrsEncoder::cycle()
{
    int ret = ERROR_SUCCESS;
    
    while (!trd->pull()) {
        if ((ret = do_cycle()) != ERROR_SUCCESS) {
            srs_warn("Encoder: Ignore error, ret=%d", ret);
        }
        
        if (!trd->pull()) {
            st_usleep(SRS_RTMP_ENCODER_CIMS * 1000);
        }
    }
    
    return ret;
}

[winlinvip]

Please notice the pull of thread:

    /**
     * Check whether thread is terminated normally or error(stopped or termianted with error),
     * and the thread should be running if it return ERROR_SUCCESS.
     * @remark Return specified error when thread terminated normally with error.
     * @remark Return ERROR_THREAD_TERMINATED when thread terminated normally without error.
     * @remark Return ERROR_THREAD_INTERRUPED when thread is interrupted.
     */
    virtual int pull();

User should ignore ERROR_THREAD_TERMINATED and ERROR_THREAD_INTERRUPED, because they just said the tread is terminated normally(without error) or interrupted by user.

[winlinvip]

Added an SrsCoroutine object and reviewed the usage of ST threads. This time, it should be done correctly. Find time to replace all the threads with this object.

TRANS_BY_GPT3

[winlinvip]

Refined.