Re: Thread save access to cout?

On Feb 26, 6:09 am, Henryk <henryk.muel...@gmx.de> wrote:


Here is a simple solution, although it may require a lot of work to
install into your source code because it requires putting a ) at the
end of each print segement:

#define COUT_LOCK(x) {std::stringstream cout;\
                      x\
                      Lock lock(mutex);\
                      std::cout << cout.str();}

int main()
{
    COUT_LOCK(cout << "Hello" << " world" << endl;)

    COUT_LOCK(
    cout << "Starting:";
    for(int i = 0; i<10; i++)
    {
        cout << i;
    }
    cout << "done." << endl;)

    return 0;
}

If your threading library has a concept of a thread id, something like
this is a little more complex, but easier to install into existing
software (actual thread safety needs to be filled in):

#include <iostream>
#include <sstream>
#include <map>

bool mutex = false;

class Lock
{
  public:
    Lock(bool & mutex) :
      mutex(mutex)
    {
        while(mutex)
        {
            // wait
        }
        mutex = true;
    }
    ~Lock()
    {
        mutex = false;
    }
  private:
    bool & mutex;
};

typedef unsigned long pthread_t;
pthread_t pthread_self()
{
    return 1ul;
}

namespace Threaded
{

class Endl
{
};
Endl endl;

class Print
{
  public:
    Print & operator<<(Endl)
    {
        if(buffers.find(pthread_self()) == buffers.end())
        {
            buffers.insert(std::pair<pthread_t, std::stringstream
*>(pthread_self(), new std::stringstream));
        }
        buffers[pthread_self()]->flush();
        Lock lock(mutex);
        std::cout << buffers[pthread_self()]->str() << std::endl;
        buffers[pthread_self()]->seekg(std::stringstream::beg);
        buffers[pthread_self()]->seekp(std::stringstream::beg);
        return *this;
    }

    template <class T>
    Print & operator<<(T const & t)
    {
        if(buffers.find(pthread_self()) == buffers.end())
        {
            buffers.insert(std::pair<pthread_t, std::stringstream
*>(pthread_self(), new std::stringstream));
        }
        *buffers[pthread_self()] << t;
        return *this;
    }

  private:
    static std::map<pthread_t, std::stringstream* > buffers;
};
std::map<pthread_t, std::stringstream *> Print::buffers;
Print cout;

};

using Threaded::cout;
using Threaded::endl;

char getSpace()
{
    cout << "In getSpace" << endl;
    return ' ';
}

int main()
{
    cout << "Hello" << getSpace() << "world." << endl;

    cout << "Starting:";
    for(int i = 0; i<10; i++)
    {
        cout << i;
    }
    cout << "done." << endl;

    return 0;
}