/usr/include/hphp/util/smalllocks.h is in hhvm-dev 3.11.1+dfsg-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 | /*
+----------------------------------------------------------------------+
| HipHop for PHP |
+----------------------------------------------------------------------+
| Copyright (c) 2010-2015 Facebook, Inc. (http://www.facebook.com) |
+----------------------------------------------------------------------+
| This source file is subject to version 3.01 of the PHP license, |
| that is bundled with this package in the file LICENSE, and is |
| available through the world-wide-web at the following url: |
| http://www.php.net/license/3_01.txt |
| If you did not receive a copy of the PHP license and are unable to |
| obtain it through the world-wide-web, please send a note to |
| license@php.net so we can mail you a copy immediately. |
+----------------------------------------------------------------------+
*/
#ifndef incl_HPHP_SMALLLOCKS_H_
#define incl_HPHP_SMALLLOCKS_H_
#include <atomic>
#include <unistd.h>
#include <iostream>
#ifdef __linux__
#include <syscall.h>
#include <linux/futex.h>
#include <sys/time.h>
#endif
namespace HPHP {
//////////////////////////////////////////////////////////////////////
#ifdef __linux__
inline int futex(int* uaddr, int op, int val, const timespec* timeout,
int* uaddr2, int val3) noexcept {
return syscall(SYS_futex, uaddr, op, val, timeout, uaddr2, val3);
}
inline void futex_wait(std::atomic<int>* value, int expected) {
futex(reinterpret_cast<int*>(value), FUTEX_WAIT_PRIVATE, expected,
nullptr, nullptr, 0);
}
inline void futex_wake(std::atomic<int>* value, int nwake) {
futex(reinterpret_cast<int*>(value), FUTEX_WAKE_PRIVATE, nwake, nullptr,
nullptr, 0);
}
#else
// On non-linux OSs we do nothing for futexes. They essentially turn into spin
// locks. If this becomes a perf issue, it's <space intentionally left blank>
inline void futex_wait(std::atomic<int>* value, int expected) {
}
inline void futex_wake(std::atomic<int>* value, int nwake) {
}
#endif
//////////////////////////////////////////////////////////////////////
/*
* A lock the size of a 4 byte int, using futex_wait when it needs to block.
*
* This structure is a standard layout class so it can be put in unions without
* declaring custom union constructors. Zeroing its storage is guaranteed to
* put it in the unlocked state, and unlocking it is guaranteed to put it back
* to all bits zero.
*
* This is roughly based on http://www.akkadia.org/drepper/futex.pdf.
*/
struct SmallLock {
void lock() {
int c = 0;
if (lock_data.compare_exchange_strong(c, 1, std::memory_order_acquire)) {
return;
}
if (c != 2) {
c = lock_data.exchange(2, std::memory_order_acquire);
}
while (c != 0) {
futex_wait(&lock_data, 2);
c = lock_data.exchange(2, std::memory_order_acquire);
}
}
void unlock() {
// Differs from "futexes are tricky" because std::atomic can't generate
// a dec instruction and test the flags.
if (lock_data.exchange(0, std::memory_order_release) != 1) {
futex_wake(&lock_data, 1);
}
}
private:
std::atomic<int> lock_data;
};
//////////////////////////////////////////////////////////////////////
}
#endif
|