提升线程开销

Question

我发现在下面这个简单的程序中，boost线程开销有三个数量级的计时开销。有没有什么方法可以减少这种开销并加速fooThread()调用？

#include <iostream>
#include <time.h>
#include <boost/thread.hpp>
#include <boost/date_time.hpp>
typedef uint64_t tick_t;
#define rdtscll(val) do { \
    unsigned int __a,__d; \
    __asm__ __volatile__("rdtsc" : "=a" (__a), "=d" (__d)); \
        (val) = ((unsigned long long)__a) | (((unsigned long long)__d)<<32); \
    } while(0)


class baseClass {
 public:
   void foo(){
             //Do nothing 
        }
       void threadFoo(){
          threadObjOne = boost::thread(&baseClass::foo, this);
              threadObjOne.join();
   }

 private:
   boost::thread threadObjOne;
 };

int main(){
   std::cout<< "main startup"<<std::endl; 
   baseClass baseObj; 
   tick_t startTime,endTime;
       rdtscll(startTime);
   baseObj.foo();
   rdtscll(endTime);
   std::cout<<"native foo() call takes "<< endTime-startTime <<" clock cycles"<<std::endl;
   rdtscll(startTime);
   baseObj.threadFoo();
       rdtscll(endTime);
       std::cout<<"Thread foo() call takes "<< endTime-startTime <<" clock cycles"<<std::endl;  
  }

您可以使用g++ -lboost_thread-mt main.cpp对其进行编译，下面是我机器上的示例输出：

main startup
native foo() call takes 2187 clock cycles
Thread foo() call takes 29630434 clock cycles

Answer 1

你真正想要的是一个线程池：

#include "threadpool.hpp"

int main()
{
    boost::threadpool::pool threadpool(8);  // I have 4 cpu's
                                            // Might be overkill need to time
                                            // to get exact numbers but depends on
                                            // blocking and other factors.

    for(int loop = 0;loop < 100000; ++loop)
    {
        // schedule 100,000 small tasks to be run in the 8 threads in the pool
        threadpool.schedule(task(loop));
    }

    // Destructor of threadpool
    // will force the main thread to wait
    // for all tasks to complete before exiting
}