Running std::thread with different argument function

Question

is it possible to create N std::thread objects, each running a while loop until the "task" list is not empty ?

It could be look like this:

Schedule sched( N );
schned.add( func1, param1, param2, param3 );
schned.add( func1, param1, param2, param3 );

schned.add( func2, param1 );

schned.add( func3, IntegerParam );
schned.add( func4, StringParam );

sched.start(); // start & join each thread wait until all threads finished

with function declaration:

bool func1( int, int, int );
bool func2( int );
bool func3( int );
bool func4( std::string );

is this possible with variadic arguments ?

@DrewDormann what do i need to store the parameter ? std::initializer_list or variadic arguments ? — Roby
– Roby, Commented Jul 15, 2015 at 5:32
Yes. Its called a thread pool. Its the first thing that anybody learning threads writes. — Loki Astari
– Loki Astari, Commented Jul 15, 2015 at 6:30

Miles Budnek · Accepted Answer · 2015-07-15 05:52:51Z

3

This should be pretty simple with std::bind and std::function so long as all of the functions have the same return type.

In your Schedule class you can just store a std::queue<std::function<bool()>>. Then have Schedule::add() look something like this:

template<typename func>
Schedule::add(func f) {
    // Appropriate synchronization goes here...
    function_queue.push_front(f);  // Will work as long as func can be converted to std::function<bool()>
}

Then you can add tasks like so:

Shedule sched(N);
// This works with function pointers
sched.add(someFunctionThatTakesNoArgs);
// And function like objects such as those returned by std::bind
sched.add(std::bind(func1, param1, param2, param3));
sched.add(std::bind(func1, param1, param2, param3));
sched.add(std::bind(func2, param1));
// Even member functions
SomeClass foo;
sched.add(std::bind(SomeClass::func3, foo, IntegerParam));
sched.add(std::bind(SomeClass::func4, foo, StringParam));

sched.start();

Then just have your worker threads do something like:

Schedule::worker() {
    // Synchronization left as an exercise for the reader...
    while (more_work_to_do) {
        std::function<bool()> f(function_queue.pop_back());
        f();
    }
}

answered Jul 15, 2015 at 5:52

Miles Budnek

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2 Comments

Roby Over a year ago

wow! i didn't know something about std::bind! big thanks for the work!

MSalters Over a year ago

@Roby: The other thing commonly stored in std::function are lambda's: [param1, param2}() { func1(param1, param2); }. The advantage is that lambda's allow more complex code: [param1, param2}() { func1(param1, ) * func2(param2); }

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