Signals and threads - good or bad design decision?
- by Jens
I have to write a program that performs highly computationally intensive calculations. The program might run for several days.
The calculation can be separated easily in different threads without the need of shared data.
I want a GUI or a web service that informs me of the current status.
My current design uses BOOST::signals2 and BOOST::thread.
It compiles and so far works as expected.
If a thread finished one iteration and new data is available it calls a signal which is connected to a slot in the GUI class.
My question(s):
Is this combination of signals and threads a wise idea? I another forum somebody advised someone else not to "go down this road".
Are there potential deadly pitfalls nearby that I failed to see?
Is my expectation realistic that it will be "easy" to use my GUI class to provide a web interface or a QT, a VTK or a whatever window?
Is there a more clever alternative (like other boost libs) that I overlooked?
following code compiles with
g++ -Wall -o main -lboost_thread-mt <filename>.cpp
code follows:
#include <boost/signals2.hpp>
#include <boost/thread.hpp>
#include <boost/bind.hpp>
#include <iostream>
#include <iterator>
#include <string>
using std::cout;
using std::cerr;
using std::string;
/**
* Called when a CalcThread finished a new bunch of data.
*/
boost::signals2::signal<void(string)> signal_new_data;
/**
* The whole data will be stored here.
*/
class DataCollector
{
typedef boost::mutex::scoped_lock scoped_lock;
boost::mutex mutex;
public:
/**
* Called by CalcThreads call the to store their data.
*/
void push(const string &s, const string &caller_name)
{
scoped_lock lock(mutex);
_data.push_back(s);
signal_new_data(caller_name);
}
/**
* Output everything collected so far to std::out.
*/
void out()
{
typedef std::vector<string>::const_iterator iter;
for (iter i = _data.begin(); i != _data.end(); ++i)
cout << " " << *i << "\n";
}
private:
std::vector<string> _data;
};
/**
* Several of those can calculate stuff.
* No data sharing needed.
*/
struct CalcThread
{
CalcThread(string name, DataCollector &datcol) :
_name(name), _datcol(datcol)
{
}
/**
* Expensive algorithms will be implemented here.
* @param num_results how many data sets are to be calculated by this thread.
*/
void operator()(int num_results)
{
for (int i = 1; i <= num_results; ++i)
{
std::stringstream s;
s << "[";
if (i == num_results)
s << "LAST ";
s << "DATA " << i << " from thread " << _name << "]";
_datcol.push(s.str(), _name);
}
}
private:
string _name;
DataCollector &_datcol;
};
/**
* Maybe some VTK or QT or both will be used someday.
*/
class GuiClass
{
public:
GuiClass(DataCollector &datcol) :
_datcol(datcol)
{
}
/**
* If the GUI wants to present or at least count the data collected so far.
* @param caller_name is the name of the thread whose data is new.
*/
void slot_data_changed(string caller_name) const
{
cout << "GuiClass knows: new data from " << caller_name << std::endl;
}
private:
DataCollector & _datcol;
};
int main()
{
DataCollector datcol;
GuiClass mc(datcol);
signal_new_data.connect(boost::bind(&GuiClass::slot_data_changed, &mc, _1));
CalcThread r1("A", datcol), r2("B", datcol), r3("C", datcol), r4("D",
datcol), r5("E", datcol);
boost::thread t1(r1, 3);
boost::thread t2(r2, 1);
boost::thread t3(r3, 2);
boost::thread t4(r4, 2);
boost::thread t5(r5, 3);
t1.join();
t2.join();
t3.join();
t4.join();
t5.join();
datcol.out();
cout << "\nDone" << std::endl;
return 0;
}
