118 lines
3.5 KiB
C++
118 lines
3.5 KiB
C++
// include/Futex.hh
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// This file is part of libpbe; see http://svn.chezphil.org/libpbe/
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// (C) 2008 Philip Endecott
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// This program is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 2 of the License, or
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// any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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#ifndef libpbe_Futex_hh
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#define libpbe_Futex_hh
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// The file implements a Futex class, which is a simple wrapper around
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// the futex syscall.
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// Futex is supported on Linux 2.6 but not older kernels. If you want to
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// run on a 2.4 kernel you need to compile with SUPPORT_LINUX_2_4 defined.
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// This will supress the content of this file and the things that use it
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// will fall back to something else (as they do on non-Linux platforms).
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#if defined(__linux__) && !defined(SUPPORT_LINUX_2_4)
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#define PBE_HAVE_FUTEX
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#include <linux/futex.h>
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#include <errno.h>
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#include <cmath>
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#include <boost/static_assert.hpp>
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#include "missing_syscalls.hh"
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#include "Exception.hh"
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namespace pbe {
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template <typename INT_T = int>
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struct Futex {
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BOOST_STATIC_ASSERT(sizeof(INT_T)==sizeof(int));
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int* const valptr;
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Futex(INT_T& val): valptr(reinterpret_cast<int*>(&val)) {}
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~Futex() {}
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void wait(INT_T expected) {
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int r = futex(valptr, FUTEX_WAIT,
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static_cast<int>(expected), NULL, NULL, 0);
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if (r==-1) {
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// There are various legitimate errors that we'll throw an exception for.
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// But there are also these, which are expected in normal operations:
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// EWOULDBLOCK - valptr != expected
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// EINTR - signal or spurious wakeup
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// We might want to return something indicating that one of these conditions
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// had occurred, but it seems that the mutex algorithm doesn't need this.
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switch (errno) {
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case EWOULDBLOCK: return;
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case EINTR: return;
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default: throw_ErrnoException("futex(FUTEX_WAIT)");
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}
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}
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}
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bool timed_wait(INT_T expected, const timespec& timeout) {
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// Returns false if timeout reached.
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int r = futex(valptr, FUTEX_WAIT,
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static_cast<int>(expected), &timeout, NULL, 0);
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if (r==-1) {
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// As above.
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switch (errno) {
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case EWOULDBLOCK: return true;
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case EINTR: return true;
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case ETIMEDOUT: return false;
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default: throw_ErrnoException("futex(FUTEX_WAIT)");
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}
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}
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return true;
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}
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bool timed_wait(INT_T expected, float timeout) {
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// Returns false if timeout reached.
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struct timespec ts;
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float timeout_whole;
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float timeout_frac;
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timeout_frac = modff(timeout, &timeout_whole);
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ts.tv_sec = static_cast<int>(timeout_whole);
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ts.tv_nsec = static_cast<int>(1e9*timeout_frac);
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return timed_wait(expected,ts);
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}
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// Wake up to n waiters; returns the number woken.
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unsigned int wake(int n=1) {
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int r = futex(valptr, FUTEX_WAKE, n, NULL, NULL, 0);
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if (r==-1) {
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throw_ErrnoException("futex(FUTEX_WAIT)");
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}
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return r;
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}
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};
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};
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#endif
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#endif
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