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Description

When waiting for a future top shows 100% CPU usage, and strace shows a steady stream of futex calls

[pid 15141] futex(0x9d19a24, FUTEX_WAIT, -2147483648, {4222429828, 3077922816}) = -1 EINVAL (Invalid argument)

You can refer to https://stackoverflow.com/questions/34259429/should-stdfuturewait-be-using-so-much-cpu-is-there-a-more-performant-call for more details on the bug.

The community already created the patches:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68921
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=231679

Steps to Reproduce

This is a code example:

#include <future>
#include <iostream>
#include <thread>
#include <unistd.h>

int main() {
  std::promise<void> p;
  auto f = p.get_future();

  std::thread t([&p](){
    std::cout << "Biding my time in a thread.\n";
    sleep(10);
    p.set_value();
  });

  std::cout << "Waiting.\n";
  f.wait();
  std::cout << "Done.\n";

  t.join();
  return 0;
}


1. Build this example test:
g++ --std=c++11 -Wall -g -o spin-wait spin-wait.cc -pthread
2.execute the binary spin-wait
./spin-wait &
3.execute the top command
During the sleeping time, the cpu usage won't be 100%.

Other Downloads

• Wind River Linux 8.0.0.26
• Wind River Linux 8.0.0.27
• Wind River Linux 8.0.0.28
• Wind River Linux 8.0.0.29
• Wind River Linux 8.0.0.30
• Wind River Linux 8.0.0.31
• Wind River Linux 8.0.0.32
• Wind River Linux 8.0.0.33
• Wind River Linux 8.0.0.34