Hello,
I am finding on Windows Vista with Microsoft Visual Studio that a call to std::condition_variable.wait() causes a busy wait. This is as if the wait() function was internally executing a for (;;) {} loop until the condition is met instead of putting the calling thread to sleep and being awakened by a change in the variable value.
I have found this with the Intel Thread Profiler, part of Intel's VTune 9.1. To be honest, I am not sure if this is a real issue or if it is just an error of the Thread Profiler in registering the state of the calling thread.
Has anyone found a similar behaviour?
If anyone wishes to test this issue, they can use the following code excerpt, which exercises the condition_variable.wait() function.
Cheers,
manuel
#include
#include
#include
#include
#include
using namespace std;
using namespace tbb;
int my_barrier;
mutex my_mutex;
condition_variable my_cond;
struct CountTask : public task
{
CountTask(unsigned int time) : m_time(time) {}
virtual task* execute()
{
Sleep(1000*m_time);
{
lock_guard lock(my_mutex);
printf("Got into thread %d\\n", my_barrier--);
my_cond.notify_one();
}
// Causes all available threads to fill up by spinning
while (true);
return 0;
}
unsigned int m_time;
};
int main() {
int n = task_scheduler_init::default_num_threads();
printf("n=%d\\n",n);
task_scheduler_init tbbinit( n+1 );
my_barrier = n;
for (int i = 0; i < n; ++i)
task::enqueue(*new (task::allocate_root()) CountTask(i));
{
unique_lock lock(my_mutex);
while (my_barrier > 0)
my_cond.wait(lock);
}
printf("done\\n");
return 0;
}
