This is the code to create a thread_group and execute all threads in parallel:
boost::thread_group group;
for (int i = 0; i < 15; ++i)
group.create_thread(aFunctionToExecute);
group.join_all();
此代码将一次执行所有线程.我想要做的是并行执行它们，但最多 4 个.当 on 终止时，将执行另一个，直到没有更多要执行为止.
This code will execute all threads at once. What I want to do is to execute them all but 4 maximum in parallel. When on is terminated, another one is executed until there are no more to execute.
Another, more efficient solution would be to have each thread callback to the primary thread when they are finished, and the handler on the primary thread could launch a new thread each time. This prevents the repetitive calls to timed_join, as the primary thread won't do anything until the callback is triggered.
