Richard Kettlewell wrote on 06/09/2015 10:16 AM:
"U.Mutlu" <for-gm...@mutluit.com> writes:
Hi,
on this page:
http://en.cppreference.com/w/cpp/thread/recursive_mutex/try_lock
they give the following C++11 example:
#include <iostream>
#include <mutex>
int main()
{
std::mutex test;
if (test.try_lock()==true) {
std::cout << "lock acquired" << std::endl;
test.unlock(); //now unlock the mutex
} else {
std::cout << "lock not acquired" << std::endl;
}
test.lock(); //to lock it again
if (test.try_lock()) { //true can be left out
std::cout << "lock acquired" << std::endl;
} else {
std::cout << "lock not acquired" << std::endl;
}
test.unlock();
}
and they say it would give this output:
Output:
lock acquired
lock not acquired
I wonder why my compiler (g++ 4.9.2 from Debian repo) gives a different output:
lock acquired
lock acquired
Which compiler is wrong, and why?
AIUI, neither is wrong. The code violates the preconditions of
try_lock(), and therefore results in undefined behavior.
Mystery solved: when using such concurrency/thread objects,
then one has to link with pthread (-lpthread):
g++ -Wall -O2 -std=gnu++11 file.cpp -lpthread
Now my compiler gives the same result.
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