change system time backward will let st-srs behavior abnormal

[suzp1984]

Root Cause

srs/trunk/3rdparty/st-srs/md.h

Lines 113 to 116 in fa8096a

	#define MD_GET_UTIME() \
	struct timeval tv; \
	(void) gettimeofday(&tv, NULL); \
	return (tv.tv_sec * 1000000LL + tv.tv_usec)

the default implementation of get timestamp of microseconds is depends on system time.

man gettimeofday

the st-srs has api that let us to config our own get timestamp function, but srs didn't config it.

srs/trunk/3rdparty/st-srs/sync.c

Lines 57 to 85 in fa8096a

	/*****************************************
	* Time functions
	*/
	st_utime_t st_utime(void)
	{
	if (_st_utime == NULL) {
	#ifdef MD_GET_UTIME
	MD_GET_UTIME();
	#else
	#error Unknown OS
	#endif
	}
	return (*_st_utime)();
	}
	int st_set_utime_function(st_utime_t (*func)(void))
	{
	if (_st_active_count) {
	errno = EINVAL;
	return -1;
	}
	_st_utime = func;
	return 0;
	}

Solutions

refactor MD_GET_UTIME or Config a time function based on more robust solutions, e.g. system uptime, the timestamp since the system boot.

Version
All version

To Reproduce
Steps to reproduce the behavior:

1. Go to 'trunk/3rdparty/st-srs/tools/helloword/'
2. run make
3. run ./helloword
4. change system time backward, e.g. change system time to one year before;
5. check the Hello print will stuck.

Expected behavior
Change the system time should not impact the st-srs behavior.

[winlinvip]

Nice work! Welcome to patch it.