BlockingConcurrentQueue::wait_dequeue_timed can't quit

[HowToExpect]

Under Linux, there will be a time synchronization operation. The current time is March 12, 2022. If set to March 1, 2022, wait_time will not return.

[cameron314]

Not sure I understand. Can you provide an example?

[HowToExpect]

`#include
#include "blockingconcurrentqueue.h"

using namespace std;
using namespace moodycamel;

void timeCallback()
{
system("date -s 2022-03-01");
}

int main()
{

BlockingConcurrentQueue<int> queue;

// current time 2022-03-21
int value = 0;
queue.wait_dequeue_timed(value, 60 * 1000 * 1000);

//have function call timeCallback();
cout << "hello world" << endl;

return 0;

}
`

hello world can't output

[cameron314]

I see! This is because POSIX semaphores use absolute deadlines based on CLOCK_REALTIME. I'll see if I can conditionally detect the presence of a glibc 2.30 extension that would work with CLOCK_MONOTONIC instead.

[HowToExpect]

I went to check the relevant information and it really has something to do with CLOCK_REALTIME

[cameron314]

Yes. Glibc 2.30+ has a non-standard sem_clockwait function that allows CLOCK_MONOTONIC time to be specified instead.

[cameron314]

Should be fixed if you have glibc 2.30+ available.

[HowToExpect]

I checked that my glibc is 2.25, so sem_clockwait is not supported, so only pthread_mutex_t and pthread_cond_t can be used to implement semaphores

[HowToExpect]

pthread_cond_timedwait() with CLOCK_MONOTONIC is supported

[HowToExpect]

pthread_mutex_t and pthread_cond_t are semaphores that I see in poco

[cameron314]

pthread_cond_t is a condition variable. It can be used to implement a semaphore but it's not as efficient. I'll see if I can add an optional alternative implementation that uses it though.