[英]C++ threading with boost asio
我有一个使用boosts库的线程池,并且在下面的示例中设置了运行两个线程,并重新运行4次。 在可以继续执行代码之前,检查is_service
以查看所有子线程执行是否完成的最佳方法是什么? 其余代码取决于程序继续运行之前所有子线程完成。 如果我进行Sleep(1000)
调用,则可以得到所需的行为,但这是不希望的,我查看了io_service_.stopped()
的检查,但始终返回0
。 任何想法将不胜感激。
#include <iostream>
#include <boost/asio/io_service.hpp>
#include <boost/bind.hpp>
#include <boost/thread/thread.hpp>
#include <vector>
#include <string>
using namespace std;
class Model {
public:
// Constructor
Model() {
work_ctrl_ = new boost::asio::io_service::work(io_service_);
for (int i = 0; i < 2; ++i) {
threads_.create_thread(
boost::bind(&boost::asio::io_service::run, &io_service_));
}
}
// Deconstructor
~Model() {
delete work_ctrl_;
}
// Function I want to thread
void manipulate_vector(unsigned start, unsigned last) {
cout << "entering manipulate vector(), from thread " << boost::this_thread::get_id() << endl;
for(unsigned k = start; k <= last; ++k)
my_vector_[k] *= sqrt(32);
cout << "exit manipulate vector()" << endl;
Sleep(500); // Add a sleep to mimic a long algorithm being executed
}
void update() {
// Do otherstuff that can't be threaded
cout << "entering update" << endl;
// run manipulate_vector() across multiple threads
// - start thread
// - execute function call.
// - stop thread
io_service_.post(boost::bind(manipulate_vector, this, 0, mid_point_));
io_service_.post(boost::bind(manipulate_vector, this, mid_point_, my_vector_.size()));
cout << io_service_.stopped() << endl;
// keep doing otherstuff that can't be threaded
cout << "hopefully the threads are finished and I can take that information and continue." << endl;
}
void run(void) {
// call update 10 times
for(unsigned i = 0; i < 4; ++i) {
update();
//Sleep(2000);
}
}
void initialise() {
// initialise vector
for(unsigned j = 0; j < 100000000; ++j)
my_vector_.push_back(j);
mid_point_ = 49999999;
}
private:
boost::asio::io_service io_service_;
boost::thread_group threads_;
boost::asio::io_service::work *work_ctrl_;
unsigned n_threads_;
vector<double> my_vector_;
unsigned mid_point_;
};
int main() {
std::cout << "----------Enter Main----------" << std::endl;
Model model;
model.initialise();
model.run();
std::cout << "----------Exit Main----------" << std::endl;
system("PAUSE");
}
大概您想知道工作何时完成,而不是线程何时停止执行(直到您调用io_service.stop()
或删除work-ctrl_
时,它们才work-ctrl_
)。
标准解决方案是使用条件变量:
std::mutex mutex;
std::condition_variable condition;
int workCount;
void manipulate_vector(unsigned start, unsigned last) {
cout << "entering manipulate vector(), from thread " << boost::this_thread::get_id() << endl;
for(unsigned k = start; k <= last; ++k)
my_vector_[k] *= sqrt(32);
cout << "exit manipulate vector()" << endl;
Sleep(500); // Add a sleep to mimic a long algorithm being executed
std::unique_lock<std::mutex> lock(mutex);
workCount--;
condition.notify_one();
}
void update() {
// Do otherstuff that can't be threaded
cout << "entering update" << endl;
// run manipulate_vector() across multiple threads
// - start thread
// - execute function call.
// - stop thread
workCount = 2;
io_service_.post(boost::bind(manipulate_vector, this, 0, mid_point_));
io_service_.post(boost::bind(manipulate_vector, this, mid_point_, my_vector_.size()));
{
std::unique_lock<std::mutex> lock(mutex);
condition.wait(lock, [&]{ return workCount == 0; });
}
}
如果您对当前线程中正在运行的某些工作没问题,可以在删除work_ctrl_
之后调用io_service_.run()
来等待。 当它返回时,没有工作了,您可以安全地继续。 您可以将线程组中的并发级别降低一级,以获取相同的整体并发性。
一种简单的替代方法是在所有帖子都排队并且删除了work_ctrl_
之后,简单地调用threads_.join_all()
。
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