MESSAGE
| DATE | 2016-11-16 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [Learn] why use a reference wrapper int his example
|
From learn-bounces-at-nylxs.com Wed Nov 16 04:22:11 2016
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To: Billy D , learn-at-nylxs.com
From: Ruben Safir
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Subject: [Learn] why use a reference wrapper int his example
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if anything, it would be the int I would think needs to be in a
reference wrapper
http://en.cppreference.com/w/cpp/thread/unique_lock
#include
#include
#include
struct Box {
explicit Box(int num) : num_things{num} {}
int num_things;
std::mutex m;
};
void transfer(Box &from, Box &to, int num)
{
// don't actually take the locks yet
std::unique_lock lock1(from.m, std::defer_lock);
std::unique_lock lock2(to.m, std::defer_lock);
// lock both unique_locks without deadlock
std::lock(lock1, lock2);
from.num_things -= num;
to.num_things += num;
// 'from.m' and 'to.m' mutexes unlocked in 'unique_lock' dtors
}
int main()
{
Box acc1(100);
Box acc2(50);
std::thread t1(transfer, std::ref(acc1), std::ref(acc2), 10);
std::thread t2(transfer, std::ref(acc2), std::ref(acc1), 5);
t1.join();
t2.join();
}
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