Basic Linux multi-process & multi-thread Programming

Today I have to make my algorithm running in parallel into order to make it faster. At the used following way to implement Multi-process:

	unsigned int proc_num = 5;
	pid_t* pids=new Pid_t[proc_num];
	Double incr= (double) n/(double) proc_num;
	
	/* Start children. * for
	(unsigned int i = 0; i < Proc_num ++i) {
		if (pids[i] = fork ()) < 0) {
	    		perror ("fork");
	    		Abort ();
	 	} else if (pids[i] = = 0) {
	    		//Doworkinchild ();

	    		Exit (0);
	  	}
	}
	
	/* Wait for children to exit. *
	/int status;
	pid_t pid;
	while (Proc_num > 0) {
	  	pid = wait (&status);
		if (status!= 0)
	  		printf ("Child Process with PID%ld aborted with status 0x%x.\n", (long) PID, status);
	  	--proc_num;  TODO (pts): Remove pid from the PIDs array.
	}

Above Way worked OK, however, there ' no way to change the ' shared ' variables into child processes. Because each child process has a independent copy of all variables.

In order to change the same array in parallel, I implemented multi threads.

struct Thread_info {/* Used as argument to Thread_start () * * pthread_t thread_id;       /* ID returned by pthread_create () */int start;      /* application-defined Thread # */int end;	/* FROM command-line argument * * int* Gpdarr;	/* Array to store GPD number/long int G;	/* Genome length */unsigned int L;	/* Read length */double L1;	GPD parameter lambda1 double L2;	GPD parameter lambda2 double M;

Maximum of GPD density};
  void Printpt (pthread_t pt) {unsigned char *PTC = (unsigned char*) (void*) (&PT);
  printf ("0x");
  For (size_t i=0 i<sizeof (PT); i++) {printf ("%02x", (unsigned) (ptc[i));
	} void* Gen_gpd_num (void* arg) {struct Thread_info *tinfo = (struct thread_info *) arg;
Do something pthread_exit (0);
	int main () {unsigned int tnum = 20;
	
	Double incr= (double) n/(double) tnum;

	thread_info* Tinfo=new Thread_info[tnum];
	int err;
	
	void* Res; /* Start children. * for (unsigned int idx=0;idx<tnum; ++idx) {tinfo[idx].start=incr*idx;
		tinfo[idx].end=incr* (idx+1);
		Tinfo[idx].gpdarr=gpdnum; TINFO[IDX].
		g=g; TINFO[IDX].
		L=l;
		TINFO[IDX].L1=L1;
		TINFO[IDX].L2=L2; TINFO[IDX].

		M=m;

		Err = Pthread_create (&tinfo[idx].thread_id, NULL, &gen_gpd_num, &tinfo[idx]);
		if (err!=0) printf ("Can" t create thread: [%s] ", strerror (err));
	else Pthread_join (tinfo[idx].thread_id, &res);
} delete [] tinfo; }

The potential problem of using multi-threading in Linux are--it is hard to figure out if there really are many threads ar e running simultaneously.

When compiling multi-threading the program using GCC, the Pthread library must be specified:

g++-O foo-wall foo.cc-l/usr/lib-lpthread

References:

How to Create Threads in Linux (with a C Example program) http://www.kernel.org/doc/man-pages/online/pages/man3 /pthread_create.3.html