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#include <cerrno>
#include <chrono>
#include <cstdint>
#include <iostream>
#include <system_error>
#include <sys/eventfd.h>
#include <thread>
#include <unistd.h>
void write_event(int efd, std::uint64_t ev) {
ssize_t n = ::write(efd, &ev, sizeof(ev));
if( n != sizeof(ev) )
throw std::system_error(errno, std::system_category(), "write");
std::cerr << "write event of " << n << " bytes." << std::endl;
}
std::uint64_t read_event(int efd) {
std::uint64_t i;
ssize_t n = ::read(efd, &i, sizeof(i));
if( n != sizeof(i) )
throw std::system_error(errno, std::system_category(), "read");
return i;
}
void foo(int efd) {
std::cout << "got event: " << read_event(efd) << std::endl;
// see what will be returned, 10 or 16? Both can be seen.
std::cout << "got event: " << read_event(efd) << std::endl;
}
int main(int argc, char** argv) {
int efd = eventfd(0, EFD_CLOEXEC);
if( efd == -1 )
throw std::system_error(errno, std::system_category(), "eventfd");
write_event(efd, 2);
std::thread t(foo, efd);
std::this_thread::sleep_for(std::chrono::milliseconds(200));
write_event(efd, 10);
write_event(efd, 6);
t.join();
return 0;
}
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