Assumes UNIX type OS. This ensures that only one instance of the calling application can run at any given time. Using the process id of the current (calling) process it obtains the link to the executable file from the /proc directory by calling stat on /proc/process_id/exe. It then examines all other sub-directories in /proc that are wholly numeric in name (the criteria for identifying current processes) to see if calling stat on subdir/exe results in a link to the same executable. If it does exit is called. If not this function simply returns allowing the calling process to proceed. Arguments: None Returns: None

Declared in file: hzProcess.h
Defined in file : hzProcess.cpp

Function Logic:

Function body:

void SingleProc (void)
{
   //  Category: Process
   //  
   //  Assumes UNIX type OS. This ensures that only one instance of the calling application can run at any given time. Using the process id of the
   //  current (calling) process it obtains the link to the executable file from the /proc directory by calling stat on /proc/process_id/exe. It
   //  then examines all other sub-directories in /proc that are wholly numeric in name (the criteria for identifying current processes) to see if
   //  calling stat on subdir/exe results in a link to the same executable. If it does exit is called. If not this function simply returns allowing
   //  the calling process to proceed.
   //  
   //  Arguments: None
   //  Returns: None
   FSTAT       fs ;                //  File status
   dirent*     pDE ;               //  Directory entry meta data
   DIR*        pDir ;              //  Operating directory
   uint32_t    ino ;               //  Inode number of directory entry
   uint32_t    cpid ;              //  Current process id
   uint32_t    xpid ;              //  Process id derived from sub-dirs of /proc
   char        buf [512];          //  Directory entry name buffer
   /*
   **  ** Obtain current executable
   **      */
   cpid = getpid() ;
   sprintf(buf, "/proc/%d/exe", cpid) ;
   if (lstat(buf, &fs) == -1)
   {
       std::cerr << "Could not stat " << buf << std::endl ;
       exit(-1);
   }
   ino = fs.st_ino ;
   /*
   **  ** Open the /proc directory and read it.
   **      */
   pDir = opendir("/proc") ;
   if (!pDir)
   {
       std::cerr << "Cannot examine processes" << std::endl ;
       exit(-3);
   }
   for (; pDE = readdir(pDir) ;)
   {
       //  Eliminate this directory and the parent
       if (pDE->d_name[0]== ''.'')
           continue ;
       //  Eliminate all non numeric directories
       if (!IsAllDigits(pDE->d_name))
           continue ;
       xpid = atoi(pDE->d_name) ;
       //  Ignore self
       if (xpid == cpid)
           continue ;
       sprintf(buf, "/proc/%d/exe", xpid) ;
       if (lstat(buf, &fs) == -1)
           std::cout << "Could not stat " << buf << std::endl ;
       else
       {
           if (fs.st_ino == ino)
           {
               std::cout << "pid: " << cpid << " - Have located an existing process of " << xpid << std::endl ;
               std::cerr << "Both the existing and current process involve executable with inode of " << ino << std::endl ;
               exit(-4);
           }
       }
   }
   closedir(pDir) ;
}