How do I deal with the system clock changing while waiting on a std::condition_variable?

Question

I\'m trying to implement some cross-platform code in C++11. Part of this code implements a semaphore object using a std::condition_variable. When I need to do a timed wait

Answer 1

I encountered the same problem. A colleague of mine gave me a tip to use certain C functions from instead and it worked out wonderfully for me.

As an example, I had:

std::mutex m_dataAccessMutex;
std::condition_variable m_dataAvailableCondition;

with its standard usage:

std::unique_lock _(m_dataAccessMutex);
// ...
m_dataAvailableCondition.notify_all();
// ...
m_dataAvailableCondition.wait_for(...); 

The above can be replaced by using pthread_mutex_t and pthread_cond_t. The advantage is that you can specify the clock to be monotonic. Brief usage example:

#include 

// Declare the necessary variables
pthread_mutex_t m_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_condattr_t m_attr;
pthread_cond_t m_cond;

// Set clock to monotonic
pthread_condattr_init(&m_attr);
pthread_condattr_setclock(&m_attr, CLOCK_MONOTONIC);
pthread_cond_init(&m_cond, &m_attr); 

// Wait on data
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
ts.tv_sec += timout_in_seconds; 
pthread_mutex_lock(&m_mutex);
int rc = pthread_cond_timedwait(&m_cond, &m_mutex, &ts);
if (rc != ETIMEDOUT)
    ; // do things with data
else 
    ; // error: timeout
// ...
pthread_mutex_unlock(&m_mutex); // have to do it manually to unlock
// ...

// Notify the data is ready
pthread_cond_broadcast(&m_cond);