main.cpp

/*
 * =====================================================================================
 *       Filename:  main.cpp
 *    Description:  Creates a child process responsible for starting a kdb daemon server
 *                  The parent process launches the gui for QScanner.
 *
 *        Version:  1.0
 *        Created:  23/04/12 15:42:19
 *       Compiler:  "make" from QScanner root. Requires qt make installed
 *                   $ sudo apt-get install libqt4-dev
 *
 *         Author:  Oliver Fletcher, ttolf@lboro.ac.uk
 *     University:  Loughborough University
 * =====================================================================================
 */

#include <QApplication>
#include "qgui.h"
#include <fcntl.h>

using namespace std;
string qLaunch;                                 /* Path to q executable */
string qRoot;                                   /* Path to QScanner root */
string qScanner;                                /* Path to Qscaner.q launch file */

/*
 * ===  FUNCTION  ======================================================================
 *         Name:  main
 *  Description:  Creates a QApplication instance. Gets a child process ID and uses it
 *                to launch the daemon server. It then executes the GUI putting the
 *                system in a permanent loop. When the GUI is closed it returns
 *                and connects to the KDB server sending a kill signal.
 * =====================================================================================
 */
int main(int argc, char *argv[])
{
  QApplication app(argc,argv);                  /* Create GUI App */
  qguiApp *dialog = new qguiApp;

  qScannerPath();                               /* Get current working directory */

  pid_t pID = fork();                           /* Create a child process id */
  if(pID > 0){
    launchDaemon();                             /* Launch the child process */
  }
  else {
    dialog->show();
    app.exec();                                 /* Execute the GUI (enter loop) */
  }

  int c = khp("localhost",5000);                /* Kill the daemon */
  k(-c,"\\\\",(K)0);
  kclose(c);

  return 0;
}

/*
 * ===  FUNCTION  ======================================================================
 *         Name:  open_or_die
 *  Description:  Opens a files. Errors if the file fails to open
 *       Source:  http://code.kx.com/wiki/Cookbook/Daemon
 * =====================================================================================
 */
int open_or_die(char *path)
{
  int file, flags = O_CREAT | O_WRONLY | O_APPEND;
  if ((NULL == path) || (-1 == (file = open (path, flags, 0666)))) {
    (void) fprintf (stderr, "Failed to open file");

    return 0;
  }
  return file;
}

/*
 * ===  FUNCTION  ======================================================================
 *         Name:  launchDaemon
 *  Description:  Uses global variables qLaunch, qScanner, qRoot to execute the
 *                server using the execv function. Redirects the program stdin, stdout
 *                and stderr to log files.
 *       Source:  http://code.kx.com/wiki/Cookbook/Daemon
 * =====================================================================================
 */
void launchDaemon()
{
  //prepare c strings to char*
  char *qlaunch = const_cast<char*> ( qLaunch.c_str() );
  char *qscan = const_cast<char*> ( qScanner.c_str() );
  char *qroot = const_cast<char*> ( qRoot.c_str() );

  char *command[] = { qlaunch , qscan  , qroot , "-p", "5000", (char *) 0};

  //Make a token attempt to see if we'll be able to exec the command.
  if (-1 == access (command[0], F_OK)) {
    (void) fprintf (stderr, "Can't access %s, exiting.\n", command[0]);
    exit(EXIT_FAILURE);
  }

  // Try to open some files for pid, stdin, stdout, stderr.
  FILE *pid_file = fopen ("logs/pid", "w+");
  int stdin_file = open_or_die("/dev/null");
  int stderr_file = open_or_die("logs/stderr");
  int stdout_file = open_or_die("logs/stdout");

  // Nuke stdin and redirect stderr, stdout.
  close (STDIN_FILENO);
  dup2 (stdin_file, STDIN_FILENO);
  close (STDOUT_FILENO);
  dup2 (stdout_file, STDOUT_FILENO);
  close (STDERR_FILENO);
  dup2 (stderr_file, STDERR_FILENO);

  // Now daemonize..
  if (0 != daemon (0, 1))  {
    printf("Error: Can't daemonize.");
    exit (EXIT_FAILURE);
  }

  // Write the pid
  fprintf (pid_file, "%d\n", getpid ());
  fclose (pid_file);

  // And away we go..
  execv (command[0], command);
}

/*
 * ===  FUNCTION  ======================================================================
 *         Name:  qScannerPath
 *  Description:  Used to find the path to the Q executable, QScanner root and QScanner
 *                executable
 *       Inputs:  None
 *      Returns:  Global Variables
 *                qLaunch -> /path/to/l32/q
 *                qRoot   -> /path/to/QScanner (folder)
 *                qScanner-> /path/to/QScanner/QScanner.q
 * =====================================================================================
 */
void qScannerPath()
{
  char buff[1024];                            /* get executable path */
  ssize_t len = readlink("/proc/self/exe", buff, sizeof(buff)-1);
  string s;

  if (len != -1) {                            /* process into string */
    buff[len] = '\0';
    s = string(buff);
  }
  for(int i=0;i<2;i++){
    s = s.substr(0,s.find_last_of("/"));      /* Remove two layers of folder depth */
  }

  qLaunch  =  s + "/l32/q";                   /* Asign Global variables */
  qRoot    =  s + "/QScanner";
  qScanner =  s + "/QScanner/QScanner.q";
}