How to specify a time duration in Boost Semaphore

Question

I'm attempting to use the timed_wait function in boost::interprocess::interprocess_semaphore.

bool timed_wait(const boost::posix_time::ptime & abs_time)

In all of the Boost documentation and Stack Overflow questions that I've researched, there doesn't appear to be a single straightforward example on how to use timed_wait for a simple duration like 5 seconds. I can't figure out how to initialize a boost::posix_time::ptime object that specifies a time duration.

The closest I've gotten is the following, which appears to immediately timeout instead of timeout after 5 seconds:

while (true)
{
    boost::posix_time::ptime wait_time(boost::interprocess::microsec_clock::local_time());
    wait_time = wait_time + boost::posix_time::microseconds(5000000);

    printf("thread 1 wait\n");
    bool result = binary_sem.timed_wait(wait_time);
    if (result == true)
    {
        printf("thread 1 acquire\n");
    }
    else
    {
        printf("timeout\n");
    }
}

Help would be greatly appreciated!

Answer 1

Looks like the base should be UTC:

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#include <boost/interprocess/sync/interprocess_semaphore.hpp>
#include <iostream>

namespace pt = boost::posix_time;

int main() {
    using clock = boost::interprocess::microsec_clock;
    boost::interprocess::interprocess_semaphore sem(3);

    auto deadline = clock::universal_time() + pt::seconds(5);

    for (auto i : {1,2,3,4})
        std::cout << "#" << i << " acquired? " << sem.timed_wait(deadline) << "\n";
}

Prints

#1 acquired? 1
#2 acquired? 1
#3 acquired? 1
#4 acquired? 0

real    0m5,005s
user    0m0,001s
sys     0m0,004s