platform/impl/socket_handle_waiter_posix.cc

// Copyright 2019 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "platform/impl/socket_handle_waiter_posix.h"

#include <time.h>

#include <algorithm>
#include <vector>

#include "platform/base/error.h"
#include "platform/impl/socket_handle_posix.h"
#include "platform/impl/timeval_posix.h"
#include "platform/impl/udp_socket_posix.h"
#include "util/osp_logging.h"

namespace openscreen {

SocketHandleWaiterPosix::SocketHandleWaiterPosix(
    ClockNowFunctionPtr now_function)
    : SocketHandleWaiter(now_function) {}

SocketHandleWaiterPosix::~SocketHandleWaiterPosix() = default;

ErrorOr<std::vector<SocketHandleWaiterPosix::HandleWithFlags>>
SocketHandleWaiterPosix::AwaitSocketsReady(
    const std::vector<SocketHandleWaiterPosix::HandleWithFlags>& sockets,
    const Clock::duration& timeout) {
  int max_fd = -1;
  fd_set read_handles{};
  fd_set write_handles{};

  FD_ZERO(&read_handles);
  FD_ZERO(&write_handles);
  for (const HandleWithFlags& hwf : sockets) {
    if (hwf.flags & Flags::kReadable) {
      FD_SET(hwf.handle.get().fd, &read_handles);
    }

    // Only add the socket to the write_handles list if it is configured for
    // write events and also has a pending write. This keeps us from polling
    // select every few nanoseconds.
    if (hwf.flags & Flags::kWritable) {
      FD_SET(hwf.handle.get().fd, &write_handles);
    }
    max_fd = std::max(max_fd, hwf.handle.get().fd);
  }
  if (max_fd < 0) {
    return Error::Code::kIOFailure;
  }

  struct timeval tv {
    ToTimeval(timeout)
  };
  // This value is set to 'max_fd + 1' by convention. Also, select() is
  // level-triggered so incomplete reads/writes by the caller are fine and will
  // be picked up again on the next select() call.  For more information, see:
  // http://man7.org/linux/man-pages/man2/select.2.html
  const int max_fd_to_watch = max_fd + 1;
  const int rv =
      select(max_fd_to_watch, &read_handles, &write_handles, nullptr, &tv);
  if (rv == -1) {
    // This is the case when an error condition is hit within the select(...)
    // command.
    return Error::Code::kIOFailure;
  } else if (rv == 0) {
    // This occurs when no sockets have a pending read.
    return Error::Code::kAgain;
  }

  std::vector<HandleWithFlags> changed_handles;
  for (const HandleWithFlags& hwf : sockets) {
    uint32_t flags = 0;
    if (FD_ISSET(hwf.handle.get().fd, &read_handles)) {
      flags |= Flags::kReadable;
    }
    if (FD_ISSET(hwf.handle.get().fd, &write_handles)) {
      flags |= Flags::kWritable;
    }
    if (flags) {
      changed_handles.push_back({hwf.handle, flags});
    }
  }
  return changed_handles;
}

void SocketHandleWaiterPosix::RunUntilStopped() {
  const bool was_running = is_running_.exchange(true);
  OSP_CHECK(!was_running);

  constexpr Clock::duration kHandleReadyTimeout = std::chrono::milliseconds(50);
  while (is_running_) {
    ProcessHandles(kHandleReadyTimeout);
  }
}

void SocketHandleWaiterPosix::RequestStopSoon() {
  is_running_.store(false);
}

}  // namespace openscreen