[英]Spurious wakeups on condition_variable with g++ and clang++
Take the following code: 请使用以下代码:
#include <iostream>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <chrono>
using namespace std;
int main() {
mutex m;
condition_variable c;
bool fired = false;
int i = 0;
// This thread counts the times the condition_variable woke up.
// If no spurious wakeups occur it should be close to 5.
thread t([&]() {
unique_lock<mutex> l(m);
while (!fired) {
c.wait_for(l, chrono::milliseconds(100));
++i;
}
});
// Here we wait for 500ms, then signal the other thread to stop
this_thread::sleep_for(chrono::milliseconds(500));
{
unique_lock<mutex> l(m);
fired = true;
c.notify_all();
cout << i << endl;
}
t.join();
}
Now, when I build this using clang++ -std=c++11 -pthread foo.cpp
everything is fine, it outputs 4
on my machine. 现在,当我使用clang++ -std=c++11 -pthread foo.cpp
它时,一切都很好,它在我的机器上输出4
。 When I build it with g++ -std=c++11 -pthread foo.cpp
however I get something very large every time, eg 81513
. 当我使用g++ -std=c++11 -pthread foo.cpp
构建它时,我每次都会得到非常大的东西,例如81513
。 I realize the number of spurious wakeups is undefined, but I was surprised to see it so high. 我意识到虚假唤醒的数量是不确定的,但我很惊讶地看到它如此之高。
Additional information: When I replace the wait_for
by a simple wait
both clang and g++ output 0
. 附加信息:当我通过简单的wait
替换wait_for
,clang和g ++输出0
。
Is this a bug / feature in g++? 这是g ++中的错误/功能吗? Why is it even different from clang? 为什么它甚至不同于铿锵? Can I get it to behave more reasonably? 我可以让它表现得更合理吗?
Also: gcc version 4.7.3 (Debian 4.7.3-4)
. 另外: gcc version 4.7.3 (Debian 4.7.3-4)
。
I managed to get g++-4.8 running, and the problem is gone. 我设法让g ++ - 4.8运行,问题就消失了。 Very weird, seems like a bug in g++-4.7.3, although I wasn't able to reproduce it on another machine. 非常奇怪,似乎是g ++ - 4.7.3中的一个错误,虽然我无法在另一台机器上重现它。
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