ceph/src/crimson/thread/Condition.h

   1 // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
   2 // vim: ts=8 sw=2 smarttab
   3
   4 #pragma once
   5
   6 #include <seastar/core/reactor.hh>
   7 #include <sys/eventfd.h>
   8
   9 namespace ceph::thread {
  10
  11 /// a synchronization primitive can be used to block a seastar thread, until
  12 /// another thread notifies it.
  13 class Condition {
  14   seastar::file_desc file_desc;
  15   int fd;
  16   seastar::pollable_fd_state fd_state;
  17   eventfd_t event = 0;
  18 public:
  19   Condition()
  20     : file_desc{seastar::file_desc::eventfd(0, 0)},
  21       fd(file_desc.get()),
  22       fd_state{std::move(file_desc)}
  23   {}
  24   seastar::future<> wait() {
  25     return seastar::engine().read_some(fd_state, &event, sizeof(event))
  26       .then([](size_t) {
  27           return seastar::now();
  28         });
  29   }
  30   void notify() {
  31     eventfd_t result = 1;
  32     ::eventfd_write(fd, result);
  33   }
  34 };
  35
  36 } // namespace ceph::thread