Created
June 22, 2011 22:03
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Code that hangs on barrier.wait()
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/* | |
compile: g++ thread_template.cpp -lboost_thread | |
Outputs: | |
BOOST_VERSION = 104200 | |
Starting thread 0 | |
Starting thread 1 | |
Thread 0 waiting for work | |
Thread 1 waiting for work | |
Threads have work... | |
*/ | |
#include <boost/version.hpp> | |
#include <boost/thread.hpp> | |
#include <boost/thread/barrier.hpp> | |
#include <boost/function.hpp> | |
#include <iostream> | |
#include <vector> | |
template<typename T> | |
class Multithreader { | |
public: | |
Multithreader() | |
: numCPU(sysconf(_SC_NPROCESSORS_ONLN)), | |
_barrier(numCPU+1), | |
mFuncs(NULL), | |
mMapTo(NULL) { | |
std::cout << "BOOST_VERSION = " << BOOST_VERSION << std::endl; | |
//Start the thread pool | |
for(long i = 0;i<numCPU;i++) { | |
std::cout << "Starting thread "<<i<< std::endl; | |
boost::thread(WorkerThread(i,this)); | |
} | |
} | |
~Multithreader() { | |
//Terminate the threads | |
//todo | |
} | |
void map(const std::vector<boost::function<T ()> >& funcs,std::vector<T>& mapTo) { | |
mFuncs = &funcs; | |
mMapTo = &mapTo; | |
std::cout << "Threads have work..." << std::endl; | |
_barrier.wait(); | |
//Workers are working at this point | |
std::cout << "Threads are working..." << std::endl; | |
_barrier.wait(); | |
std::cout << "Threads have finished" << std::endl; | |
} | |
private: | |
const std::vector<boost::function<T ()> >* mFuncs; | |
std::vector<T>* mMapTo; | |
boost::barrier _barrier; | |
size_t numCPU; | |
class WorkerThread { | |
public: | |
WorkerThread(long _id,Multithreader* _parent) | |
: id(_id),parent(_parent) { | |
} | |
void operator()() { | |
while(true) { | |
std::cout << "Thread "<<id<<" waiting for work" << std::endl; | |
parent->_barrier.wait(); | |
std::cout << "Thread "<<id<<" has work" << std::endl; | |
//Do work | |
for(long i = id;i<parent->mFuncs->size();i+=parent->numCPU) { | |
parent->mMapTo->at(i) = parent->mFuncs->at(i)(); | |
} | |
parent->_barrier.wait(); | |
std::cout << "Thread "<<id<<" finished the work" << std::endl; | |
} | |
} | |
long id; | |
Multithreader* parent; | |
}; | |
}; | |
#include <boost/bind.hpp> | |
double f(double x) { | |
return x*2; | |
} | |
int main() { | |
//Start the thread pool | |
Multithreader<double> mt; | |
std::vector<boost::function<double()> > work;work.resize(20); | |
std::vector<double> results;results.resize(20); | |
//Prepare the work | |
for(unsigned long i = 0;i<20;i++) { | |
work[i] = boost::bind(f,i); | |
} | |
//Execute in parallel | |
mt.map(work,results); | |
while(true) { | |
//For the purposes of the example, keep the main thread alive | |
//so we don't delete mt | |
} | |
} |
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