Listing 3. Allocating Threads
int main (int argc, char *argv[]){
int num_threads(2);
// were we called properly?
if (argc<3)
usage(argv[0]);
if (argc==4)
num_threads=atol(argv[3]);
try {
pthread_t *t_id=new pthread_t[num_threads];
CountPrimes **counter=
new CountPrimes*[num_threads];
// start up the threads
long start(atol(argv[1]));
long stop(atol(argv[2]));
long incr((stop-start)/num_threads);
for (int i=0; i<num_threads; i++){
counter[i]=new CountPrimes(start,
(start+incr)>stop?stop:start+incr);
start+=incr+1;
pthread_create(&t_id[i],NULL,
counter[i]->entry,counter[i]);
}
// now wait for the results
long count=0;
for (int i=0; i<num_threads; i++){
void *return_val;
pthread_join(t_id[i],&return_val);
count+=*(reinterpret_cast<long*>(return_val));
delete reinterpret_cast<long*>(return_val);
}
for (int i=0; i<num_threads; i++)
delete counter[i];
delete[] counter;
delete[] t_id;
if (count>1){
cout << "There were " << count;
cout << " primes." << endl;
}
else{
cout << "There was " << count;
cout << " prime." << endl;
}
}
catch (range_error e){
cout << "Exception: " << e.what() << endl;
exit(EXIT_FAILURE);
}
return EXIT_SUCCESS;
}
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