atomic_queue.c File Reference

Thread-safe queues. More...

#include <stdint.h>
#include <stdalign.h>
#include <inttypes.h>
#include <freeradius-devel/autoconf.h>
#include <freeradius-devel/io/atomic_queue.h>
#include <freeradius-devel/util/talloc.h>
#include <freeradius-devel/util/math.h>

Include dependency graph for atomic_queue.c:

Go to the source code of this file.

Data Structures
struct	fr_atomic_queue_entry_t
	Entry in the queue. More...
struct	fr_atomic_queue_s
	Structure to hold the atomic queue. More...

Macros
#define	acquire(_var)   atomic_load_explicit(&_var, memory_order_acquire)
#define	atomic_int64_t   _Atomic(int64_t)
#define	atomic_uint32_t   _Atomic(uint32_t)
#define	atomic_uint64_t   _Atomic(uint64_t)
#define	CACHE_LINE_SIZE   64
#define	cas_decr(_store, _var)   atomic_compare_exchange_strong_explicit(&_store, &_var, _var - 1, memory_order_release, memory_order_relaxed)
#define	cas_incr(_store, _var)   atomic_compare_exchange_strong_explicit(&_store, &_var, _var + 1, memory_order_release, memory_order_relaxed)
#define	load(_var)   atomic_load_explicit(&_var, memory_order_relaxed)
#define	store(_store, _var)   atomic_store_explicit(&_store, _var, memory_order_release)

Functions
fr_atomic_queue_t *	fr_atomic_queue_alloc (TALLOC_CTX *ctx, size_t size)
	Create fixed-size atomic queue.
void	fr_atomic_queue_debug (FILE *fp, fr_atomic_queue_t *aq)
	Dump an atomic queue.
void	fr_atomic_queue_free (fr_atomic_queue_t **aq)
	Free an atomic queue if it's not freed by ctx.
bool	fr_atomic_queue_pop (fr_atomic_queue_t *aq, void **p_data)
	Pop a pointer from the atomic queue.
bool	fr_atomic_queue_push (fr_atomic_queue_t *aq, void *data)
	Push a pointer into the atomic queue.
size_t	fr_atomic_queue_size (fr_atomic_queue_t *aq)

Detailed Description

Thread-safe queues.

Id

7a4d7837f69247a69624f8b33786b9b1587175c1

This is an implementation of a bounded MPMC ring buffer with per-slot sequence numbers, described by Dmitry Vyukov.

Copyright

2016 Alan DeKok (aland.nosp@m.@fre.nosp@m.eradi.nosp@m.us.o.nosp@m.rg)

2016 Alister Winfield

Definition in file atomic_queue.c.

---

Data Structure Documentation

fr_atomic_queue_entry_t

struct fr_atomic_queue_entry_t

Entry in the queue.

Note

This structure is cache line aligned for modern AMD/Intel CPUs. This is to avoid contention when the producer and consumer are executing on different CPU cores.

Definition at line 62 of file atomic_queue.c.

Data Fields
void *	data
atomic_int64_t	seq	Must be seq then data to ensure seq is 64bit aligned for 32bit address spaces.

fr_atomic_queue_s

struct fr_atomic_queue_s

Structure to hold the atomic queue.

Note

DO NOT redorder these fields without understanding how alignas works and maintaining separation. The head and tail must be in different cache lines to reduce contention between producers and consumers. Cold data (size, chunk) can share a line, but must be separated from head and tail and entry.

Definition at line 76 of file atomic_queue.c.

Collaboration diagram for fr_atomic_queue_s:

Data Fields
void *	chunk	The start of the talloc chunk to pass to free. We need to play tricks to get aligned memory with talloc.
fr_atomic_queue_entry_t	entry[]	The entry array, also aligned to ensure it's not in the same cache line as tail and size.
atomic_int64_t	head	Position of the producer. Cache aligned bytes to ensure it's in a different cache line to tail to reduce memory contention.
size_t	size	The length of the queue. This is static. Also needs to be cache aligned, otherwise it can end up directly after tail in memory and share a cache line.
atomic_int64_t	tail	Position of the consumer. Cache aligned bytes to ensure it's in a different cache line to tail to reduce memory contention. Reads may still need to occur from size whilst the producer is writing to tail.

Macro Definition Documentation

acquire

#define acquire

(

_var

)

atomic_load_explicit(&_var, memory_order_acquire)

Definition at line 51 of file atomic_queue.c.

atomic_int64_t

#define atomic_int64_t   _Atomic(int64_t)

Definition at line 44 of file atomic_queue.c.

atomic_uint32_t

#define atomic_uint32_t   _Atomic(uint32_t)

Definition at line 45 of file atomic_queue.c.

atomic_uint64_t

#define atomic_uint64_t   _Atomic(uint64_t)

Definition at line 46 of file atomic_queue.c.

CACHE_LINE_SIZE

#define CACHE_LINE_SIZE   64

Definition at line 54 of file atomic_queue.c.

cas_decr

#define cas_decr	(		_store,
			_var
	)		atomic_compare_exchange_strong_explicit(&_store, &_var, _var - 1, memory_order_release, memory_order_relaxed)

Definition at line 49 of file atomic_queue.c.

cas_incr

#define cas_incr	(		_store,
			_var
	)		atomic_compare_exchange_strong_explicit(&_store, &_var, _var + 1, memory_order_release, memory_order_relaxed)

Definition at line 48 of file atomic_queue.c.

load

#define load

(

_var

)

atomic_load_explicit(&_var, memory_order_relaxed)

Definition at line 50 of file atomic_queue.c.

store

#define store	(		_store,
			_var
	)		atomic_store_explicit(&_store, _var, memory_order_release)

Definition at line 52 of file atomic_queue.c.

Function Documentation

fr_atomic_queue_alloc()

fr_atomic_queue_t * fr_atomic_queue_alloc	(	TALLOC_CTX *	ctx,
		size_t	size
	)

Create fixed-size atomic queue.

Note

the queue must be freed explicitly by the ctx being freed, or by using the fr_atomic_queue_free function.

Parameters

[in]	ctx	The talloc ctx to allocate the queue in.
[in]	size	The number of entries in the queue.

Returns

• NULL on error.
• fr_atomic_queue_t *, a pointer to the allocated and initialized queue.

Definition at line 114 of file atomic_queue.c.

Here is the call graph for this function:

Here is the caller graph for this function:

fr_atomic_queue_debug()

void fr_atomic_queue_debug	(	FILE *	fp,
		fr_atomic_queue_t *	aq
	)

Dump an atomic queue.

Absolutely NOT thread-safe.

Parameters

[in]	aq	The atomic queue to debug.
[in]	fp	where the debugging information will be printed.

Definition at line 408 of file atomic_queue.c.

Here is the caller graph for this function:

fr_atomic_queue_free()

void fr_atomic_queue_free

(

fr_atomic_queue_t **

aq

)

Free an atomic queue if it's not freed by ctx.

This function is needed because the atomic queue memory must be cache line aligned.

Definition at line 171 of file atomic_queue.c.

Here is the call graph for this function:

fr_atomic_queue_pop()

bool fr_atomic_queue_pop	(	fr_atomic_queue_t *	aq,
		void **	p_data
	)

Pop a pointer from the atomic queue.

Parameters

[in]	aq	the atomic queue to retrieve data from.
[out]	p_data	where to write the data.

Returns

• true on successful pop
• false on queue empty

Definition at line 310 of file atomic_queue.c.

Here is the caller graph for this function:

fr_atomic_queue_push()

bool fr_atomic_queue_push	(	fr_atomic_queue_t *	aq,
		void *	data
	)

Push a pointer into the atomic queue.

Parameters

[in]	aq	The atomic queue to add data to.
[in]	data	to push.

Returns

• true on successful push
• false on queue full

Definition at line 187 of file atomic_queue.c.

Here is the call graph for this function:

Here is the caller graph for this function:

fr_atomic_queue_size()

size_t fr_atomic_queue_size

(

fr_atomic_queue_t *

aq

)

Definition at line 372 of file atomic_queue.c.

Here is the caller graph for this function: