I am getting a C++ error with threading:
terminate called without an active exception
Aborted
Here is the code:
#include <queue>
#include <thread>
#include <mutex>
#include <condition_variable>
template<typename TYPE>
class blocking_stream
{
public:
blocking_stream(size_t max_buffer_size_)
: max_buffer_size(max_buffer_size_)
{
}
//PUSH data into the buffer
blocking_stream &operator<<(TYPE &other)
{
std::unique_lock<std::mutex> mtx_lock(mtx);
while(buffer.size()>=max_buffer_size)
stop_if_full.wait(mtx_lock);
buffer.push(std::move(other));
mtx_lock.unlock();
stop_if_empty.notify_one();
return *this;
}
//POP data out of the buffer
blocking_stream &operator>>(TYPE &other)
{
std::unique_lock<std::mutex> mtx_lock(mtx);
while(buffer.empty())
stop_if_empty.wait(mtx_lock);
other.swap(buffer.front());
buffer.pop();
mtx_lock.unlock();
stop_if_full.notify_one();
return *this;
}
private:
size_t max_buffer_size;
std::queue<TYPE> buffer;
std::mutex mtx;
std::condition_variable stop_if_empty,
stop_if_full;
bool eof;
};
I modeled my code around this example: http://www.justsoftwaresolutions.co.uk/threading/implementing-a-thread-safe-queue-using-condition-variables.html
What am I doing wrong and how do I fix the error?
This question is related to
c++
multithreading
deadlock
c++11
How to reproduce that error:
#include <iostream>
#include <stdlib.h>
#include <string>
#include <thread>
using namespace std;
void task1(std::string msg){
cout << "task1 says: " << msg;
}
int main() {
std::thread t1(task1, "hello");
return 0;
}
Compile and run:
el@defiant ~/foo4/39_threading $ g++ -o s s.cpp -pthread -std=c++11
el@defiant ~/foo4/39_threading $ ./s
terminate called without an active exception
Aborted (core dumped)
You get that error because you didn't join or detach your thread.
One way to fix it, join the thread like this:
#include <iostream>
#include <stdlib.h>
#include <string>
#include <thread>
using namespace std;
void task1(std::string msg){
cout << "task1 says: " << msg;
}
int main() {
std::thread t1(task1, "hello");
t1.join();
return 0;
}
Then compile and run:
el@defiant ~/foo4/39_threading $ g++ -o s s.cpp -pthread -std=c++11
el@defiant ~/foo4/39_threading $ ./s
task1 says: hello
The other way to fix it, detach it like this:
#include <iostream>
#include <stdlib.h>
#include <string>
#include <unistd.h>
#include <thread>
using namespace std;
void task1(std::string msg){
cout << "task1 says: " << msg;
}
int main()
{
{
std::thread t1(task1, "hello");
t1.detach();
} //thread handle is destroyed here, as goes out of scope!
usleep(1000000); //wait so that hello can be printed.
}
Compile and run:
el@defiant ~/foo4/39_threading $ g++ -o s s.cpp -pthread -std=c++11
el@defiant ~/foo4/39_threading $ ./s
task1 says: hello
Read up on detaching C++ threads and joining C++ threads.
As long as your program die, then without detach or join of the thread, this error will occur. Without detaching and joining the thread, you should give endless loop after creating thread.
int main(){
std::thread t(thread,1);
while(1){}
//t.detach();
return 0;}
It is also interesting that, after sleeping or looping, thread can be detach or join. Also with this way you do not get this error.
Below example also shows that, third thread can not done his job before main die. But this error can not happen also, as long as you detach somewhere in the code. Third thread sleep for 8 seconds but main will die in 5 seconds.
void thread(int n) {std::this_thread::sleep_for (std::chrono::seconds(n));}
int main() {
std::cout << "Start main\n";
std::thread t(thread,1);
std::thread t2(thread,3);
std::thread t3(thread,8);
sleep(5);
t.detach();
t2.detach();
t3.detach();
return 0;}
Eric Leschinski and Bartosz Milewski have given the answer already. Here, I will try to present it in a more beginner friendly manner.
Once a thread has been started within a scope (which itself is running on a thread), one must explicitly ensure one of the following happens before the thread goes out of scope:
Note, by the time the thread is joined with or detached, it may have well finished executing. Still either of the two operations must be performed explicitly.
year, the thread must be join(). when the main exit
First you define a thread. And if you never call join() or detach() before calling the thread destructor, the program will abort.
As follows, calling a thread destructor without first calling join (to wait for it to finish) or detach is guarenteed to immediately call std::terminate and end the program.
Either implicitly detaching or joining a joinable() thread in its destructor could result in difficult to debug correctness (for detach) or performance (for join) bugs encountered only when an exception is raised. Thus the programmer must ensure that the destructor is never executed while the thread is still joinable.
Source: Stackoverflow.com