change system time backward will let st-srs behavior abnormal

[Jacob Su]

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.

[Winlin]

Nice work! Welcome to patch it.