public member function
<condition_variable>

std::condition_variable::notify_all

void notify_all() noexcept;
Notify all
Unblocks all threads currently waiting for this condition.

If no threads are waiting, the function does nothing.

Parameters

none

Return value

none

Example

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
// condition_variable::notify_all
#include <iostream>           // std::cout
#include <thread>             // std::thread
#include <mutex>              // std::mutex, std::unique_lock
#include <condition_variable> // std::condition_variable

std::mutex mtx;
std::condition_variable cv;
bool ready = false;

void print_id (int id) {
  std::unique_lock<std::mutex> lck(mtx);
  while (!ready) cv.wait(lck);
  // ...
  std::cout << "thread " << id << '\n';
}

void go() {
  std::unique_lock<std::mutex> lck(mtx);
  ready = true;
  cv.notify_all();
}

int main ()
{
  std::thread threads[10];
  // spawn 10 threads:
  for (int i=0; i<10; ++i)
    threads[i] = std::thread(print_id,i);

  std::cout << "10 threads ready to race...\n";
  go();                       // go!

  for (auto& th : threads) th.join();

  return 0;
}


Possible output (thread order may vary):

10 threads ready to race...
thread 6
thread 2
thread 5
thread 3
thread 4
thread 1
thread 7
thread 0
thread 9
thread 8

Data races

No data races (atomic operation).
Atomic operations on the object are ordered according to a single total order.

Exception safety

No-throw guarantee: never throws exceptions.

See also