libcruft-util/cruft/util/thread/event_futex.cpp

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/*
2018-08-04 15:14:06 +10:00
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* Copyright 2018 Danny Robson <danny@nerdcruft.net>
*/
#include "event.hpp"
#include "../cast.hpp"
#include "../posix/except.hpp"
#include <cerrno>
#include <linux/futex.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <limits>
using cruft::thread::event;
///////////////////////////////////////////////////////////////////////////////
static long
sys_futex (void *addr1, int op, int val1, struct timespec *timeout, void *addr2, int val3)
{
return syscall (SYS_futex, addr1, op | FUTEX_PRIVATE_FLAG, val1, timeout, addr2, val3);
}
///////////////////////////////////////////////////////////////////////////////
event::event ():
value (0)
{ ; }
///////////////////////////////////////////////////////////////////////////////
void
event::wait (void)
{
for (auto observed = value.load (); observed == value.load (); ) {
auto res = sys_futex (&value, FUTEX_WAIT, observed, nullptr, nullptr, 0);
if (res < 0) {
switch (errno) {
case EAGAIN: return;
case EINTR: continue;
}
posix::error::throw_code ();
}
}
}
///////////////////////////////////////////////////////////////////////////////
int
event::notify_all (void)
{
return notify (std::numeric_limits<int>::max ());
}
//-----------------------------------------------------------------------------
int
event::notify (int count)
{
++value;
auto res = sys_futex (&value, FUTEX_WAKE, count, nullptr, nullptr, 0);
if (res < 0)
posix::error::throw_code ();
return cruft::cast::narrow<int> (res);
}