/usr/include/gdnsd/stats.h is in gdnsd-dev 2.2.0-1ubuntu1.
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 | /* Copyright © 2012 Brandon L Black <blblack@gmail.com>
*
* This file is part of gdnsd.
*
* gdnsd is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* gdnsd is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with gdnsd. If not, see <http://www.gnu.org/licenses/>.
*
*/
#ifndef GDNSD_STATS_H
#define GDNSD_STATS_H
#include <gdnsd/compiler.h>
#include <gdnsd/dmn.h>
#include <inttypes.h>
/*
* This header defines two data types named stats_t and stats_uint_t,
* and several accessor functions for them.
*
* stats_t is used to implement an uint-like peice of data which is
* shared (without barriers or locking) between multiple threads
* and/or CPUs with the following very important caveats:
*
* 1) One thread is the "owner", and is the only thread performing
* write operations to the value within stats_t.
* 2) Non-owner threads only read the data, using stats_get().
* 3) The usage of the stats_t must be such that there are no data
* dependencies on it for correctness. In other words: pay attention
* to the word "stats" in the type name; this is intended for storing
* and retrieving statistical data which have no bearing on correct
* program execution.
* 4) Further, it's important to realize that the writes will only
* be seen by the non-owner threads "when the CPU feels like it". On
* modern mainstream systems with reasonable cache coherency, this
* generally happens "pretty soon", soon enough that it doesn't matter
* for stats accounting. There is no actual gaurantee on when the
* update becomes visible in the general case, and it might *never*
* become visible on some exotic architectures that gdnsd doesn't
* care to support at this time.
*
* stats_uint_t is simply an regular unsigned type of some width that
* matches the internal width of stats_t. You can store the result
* of stats_get() in such a type to cache it thread-locally for a while
* in cases where that makes sense.
*
* The width of the types currently matches uintptr_t (the width of a
* pointer), because most mainstream architectures are atomic for
* this size of aligned memory access (not atomic in the SMP sense,
* atomic in the "you won't read a half-updated value" sense).
*/
typedef uintptr_t stats_uint_t;
typedef struct { stats_uint_t _x; } stats_t;
// stats_own_set() -> set the stats value from the owner thread only
F_NONNULL F_UNUSED
static void stats_own_set(stats_t* s, const stats_uint_t v)
{ dmn_assert(s); s->_x = v; }
// stats_own_inc() -> increment stats value from the owner thread only
F_NONNULL F_UNUSED
static void stats_own_inc(stats_t* s)
{ dmn_assert(s); s->_x++; }
// stats_own_get() -> read the value from the owner thread
F_NONNULL F_UNUSED
static stats_uint_t stats_own_get(const stats_t* s)
{ dmn_assert(s); return s->_x; }
// stats_get() -> read the value from any other thread
F_NONNULL F_UNUSED
static stats_uint_t stats_get(const stats_t* s)
{ dmn_assert(s); return *(const volatile stats_uint_t*)&s->_x; }
#endif // GDNSD_STATS_H
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