How to pass data to thread
Hi, I want to pass data to a thread function. My question is- what is wrong with this code? The compiler error output is: "error: function returning a function". In the code below I am trying to pass an int to the thread function. // ------------- code: how to pass data to the thread ? ---------------- #include <boost/thread/thread.hpp> #include <boost/bind.hpp> #include <iostream> using namespace std; class TestThread { public: void thread(int a); void CreateThreads(void); }; void TestThread::thread(int a) { cout << "I am thread " << a << endl; } void TestThread::CreateThreads() { boost::thread t1( boost::bind( &TestThread::thread, 10)); boost::thread t2( boost::bind( &TestThread::thread, 20)); // wait for the thread to finish t1.join(); t2.join(); } int main() { TestThread t; t.CreateThreads(); }
Monica Gretzer wrote:
Hi,
I want to pass data to a thread function. My question is- what is wrong with this code? The compiler error output is: "error: function returning a function". In the code below I am trying to pass an int to the thread function.
// ------------- code: how to pass data to the thread ? ---------------- #include <boost/thread/thread.hpp> #include <boost/bind.hpp> #include <iostream>
using namespace std;
class TestThread { public: void thread(int a); void CreateThreads(void); };
void TestThread::thread(int a) { cout << "I am thread " << a << endl; }
void TestThread::CreateThreads() { boost::thread t1( boost::bind( &TestThread::thread, 10)); boost::thread t2( boost::bind( &TestThread::thread, 20));
The ::thread method is non-static, and you don't pass any object to bind. You should have boost::bind (&TestThread::thread, some_object, 10) HTH, Volodya
Vladimir Prus wrote:
Monica Gretzer wrote:
void TestThread::thread(int a) { cout << "I am thread " << a << endl; }
void TestThread::CreateThreads() { boost::thread t1( boost::bind( &TestThread::thread, 10)); boost::thread t2( boost::bind( &TestThread::thread, 20));
The ::thread method is non-static, and you don't pass any object to bind. You should have
boost::bind (&TestThread::thread, some_object, 10)
... or, in this case, since you probably want to call this->thread( 10 ) in a thread, you need boost::thread t1( boost::bind( &TestThread::thread, this, 10)); boost::thread t2( boost::bind( &TestThread::thread, this, 20));
Hi, Thanks for your answers. Now I wonder how to a certain number of threads which is decided at runtime and can vary between program runs. I send the number of threads as an argument to CreateThreads. // ----------- create a number of threads that is known at runtime -------- #include <boost/thread/thread.hpp> #include <boost/bind.hpp> #include <iostream> using namespace std; class TestThread { public: void thread(int a); void CreateThreads(int nb); }; void TestThread::thread(int a) { cout << "I am thread " << a << "." << endl; } void TestThread::CreateThreads(int nb) { boost::thread t1( boost::bind( &TestThread::thread, this, 1)); boost::thread t2( boost::bind( &TestThread::thread, this, 2)); boost::thread t3( boost::bind( &TestThread::threas, this, 3)); t1.join(); t2.join(); t3.join(); } int main() { TestThread t; t.CreateThreads(3); } // ------------------------------------------------------------------ The argument to CreateThreads, ("nb", the number of threads that shall be created, in this case 3), will be known at runtime (the number of threads in my application will be in the interval [1,11]). In the code above I don't use the argument ("nb") passed to CreateThreads and the code will always create 3 threads. How do I change the code in CreateThreads to make it use the "nb" argument and create the specified number of threads? Thanks in advance Monica Gretzer Peter Dimov <pdimov@mmltd.net> skrev: Vladimir Prus wrote:
Monica Gretzer wrote:
void TestThread::thread(int a) { cout << "I am thread " << a << endl; }
void TestThread::CreateThreads() { boost::thread t1( boost::bind( &TestThread::thread, 10)); boost::thread t2( boost::bind( &TestThread::thread, 20));
The ::thread method is non-static, and you don't pass any object to bind. You should have
boost::bind (&TestThread::thread, some_object, 10)
... or, in this case, since you probably want to call this->thread( 10 ) in a thread, you need boost::thread t1( boost::bind( &TestThread::thread, this, 10)); boost::thread t2( boost::bind( &TestThread::thread, this, 20)); _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
Monica Gretzer wrote:
Hi,
Thanks for your answers. Now I wonder how to a certain number of threads which is decided at runtime and can vary between program runs. I send the number of threads as an argument to CreateThreads.
[...]
void TestThread::CreateThreads(int nb) { boost::thread t1( boost::bind( &TestThread::thread, this, 1)); boost::thread t2( boost::bind( &TestThread::thread, this, 2)); boost::thread t3( boost::bind( &TestThread::threas, this, 3));
t1.join(); t2.join(); t3.join(); }
If you really like to wait for the threads to finish (which is what you do with tN.join), you need to use a thread_group: http://www.boost.org/doc/html/thread_group.html void TestThread::CreateThreads(int nb) { boost::thread_group tg; for( int i = 0; i < nb; ++i ) { tg.create_thread( boost::bind( &TestThread::thread, this, i ) ); } tg.join_all(); }
Monica Gretzer wrote:
Hi,
I want to pass data to a thread function. My question is- what is wrong with this code? The compiler error output is: "error: function returning a function". In the code below I am trying to pass an int to the thread function.
// ------------- code: how to pass data to the thread ? ---------------- #include <boost/thread/thread.hpp> #include <boost/bind.hpp> #include <iostream>
using namespace std;
class TestThread { public: void thread(int a); void CreateThreads(void); };
void TestThread::thread(int a) { cout << "I am thread " << a << endl; }
void TestThread::CreateThreads() { boost::thread t1( boost::bind( &TestThread::thread, 10)); boost::thread t2( boost::bind( &TestThread::thread, 20));
// wait for the thread to finish t1.join(); t2.join(); }
int main() { TestThread t; t.CreateThreads(); } hi monica,
either make TestThread::thread static ... class TestThread { ... static void thread(int a); ... }; or use an instance of TestThread to bind to... void TestThread::CreateThreads() { TestThread tt; boost::thread t1( boost::bind( &TestThread::thread, tt, 10)); ... } -- HTH dave
participants (4)
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David Klein -
Monica Gretzer -
Peter Dimov -
Vladimir Prus