Can someone give me a TBB example how to:
Here's a couple of complete examples, one using parallel_for
, the other using parallel_for_each
.
Update 2014-04-12: These show what I'd consider to be a pretty old fashioned way of using TBB now; I've added a separate answer using parallel_for
with a C++11 lambda.
#include "tbb/blocked_range.h"
#include "tbb/parallel_for.h"
#include "tbb/task_scheduler_init.h"
#include <iostream>
#include <vector>
struct mytask {
mytask(size_t n)
:_n(n)
{}
void operator()() {
for (int i=0;i<1000000;++i) {} // Deliberately run slow
std::cerr << "[" << _n << "]";
}
size_t _n;
};
struct executor
{
executor(std::vector<mytask>& t)
:_tasks(t)
{}
executor(executor& e,tbb::split)
:_tasks(e._tasks)
{}
void operator()(const tbb::blocked_range<size_t>& r) const {
for (size_t i=r.begin();i!=r.end();++i)
_tasks[i]();
}
std::vector<mytask>& _tasks;
};
int main(int,char**) {
tbb::task_scheduler_init init; // Automatic number of threads
// tbb::task_scheduler_init init(2); // Explicit number of threads
std::vector<mytask> tasks;
for (int i=0;i<1000;++i)
tasks.push_back(mytask(i));
executor exec(tasks);
tbb::parallel_for(tbb::blocked_range<size_t>(0,tasks.size()),exec);
std::cerr << std::endl;
return 0;
}
and
#include "tbb/parallel_for_each.h"
#include "tbb/task_scheduler_init.h"
#include <iostream>
#include <vector>
struct mytask {
mytask(size_t n)
:_n(n)
{}
void operator()() {
for (int i=0;i<1000000;++i) {} // Deliberately run slow
std::cerr << "[" << _n << "]";
}
size_t _n;
};
template <typename T> struct invoker {
void operator()(T& it) const {it();}
};
int main(int,char**) {
tbb::task_scheduler_init init; // Automatic number of threads
// tbb::task_scheduler_init init(4); // Explicit number of threads
std::vector<mytask> tasks;
for (int i=0;i<1000;++i)
tasks.push_back(mytask(i));
tbb::parallel_for_each(tasks.begin(),tasks.end(),invoker<mytask>());
std::cerr << std::endl;
return 0;
}
Both compile on a Debian/Wheezy (g++ 4.7) system with g++ tbb_example.cpp -ltbb
(then run with ./a.out
)
(See this question for replacing that "invoker
" thing with a std::mem_fun_ref
or boost::bind
).