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#ifndef RECORDER_RING_H
#define RECORDER_RING_H
// *****************************************************************************
// recorder_ring.h Recorder project
// *****************************************************************************
//
// File description:
//
// A ring (circular buffer) with multiple writers, generally single reader.
//
// This implementation is supposed to work in multi-CPU configurations
// without using locks, only using atomic primitives
//
//
//
//
//
// *****************************************************************************
// This software is licensed under the GNU Lesser General Public License v2+
// (C) 2017-2019, Christophe de Dinechin <christophe@dinechin.org>
// *****************************************************************************
// This file is part of Recorder
//
// Recorder is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 2 of the License, or
// (at your option) any later version.
//
// Recorder 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with Recorder, in a file named COPYING.
// If not, see <https://www.gnu.org/licenses/>.
// *****************************************************************************
/*
* Implementation of a thread-safe, non-blocking ring buffer.
* This ring buffer can work in multi-processor scenarios or multi-threaded
* systems, and can be used to store records of any type. It can also safely
* manage sequences of consecutive records. A typical use case is strings
* in a console print buffer, which have variable length.
*
* How this works:
* Each buffer is represented by
* - an array A of N items (for performance, N should be a power of 2),
* - a reader index R,
* - a writer index W
* - a commit index C
* - an overflow counter O
*
* The core invariants of the structure are (ignoring integer overflow)
* 1. R <= C <= W
* 2. overflowed = W - R >= N
*
* Reading entries from the buffer consist in the following steps:
* 1. If the buffer overflowed, "catch up":
* 1a. Set R to W-N+1
* 2b. Increase O to record the overflow
* 2. There is readable data iff R < C. If so:
* 2a. Read A[R % N] (possibly blocking)
* 2b. Atomically increase R
*
* Writing E entries in the buffer consists in the following steps:
* 1. Atomically increase W, fetching the old W (fetch_and_add)
* 2. Copy the entries in A[oldW % N] (possibly blocking)
* 3. Wait until C == oldW, and Atomically set C to W (possibly blocking)
*
* Step 2 can block if the reader has not caught up yet.
* Step 3 can block if another writer has still not updated C
*
* Important notes:
* The code as written is safe for use with C++ objects. Do not attempt
* to replace data copies with memcpy(), as it would most likely not
* improve speed (because of the "modulo" to perform) and would break C++.
*
* In theory, if you use the buffer long enough, all indexes will ultimately
* wrap around. This is why all comparisons are done with something like
* (int) (writer - reader) >= size
* instead of a solution that would fail when writer wraps around
* writer >= reader + size
* It is therefore assumed that you will never create a buffer of a
* size larger than 2^31 on a 32-bit machine. Probably OK.
*
*/
// ****************************************************************************
//
// If .h included from a C++ program, select the C++ version
//
// ****************************************************************************
#include <stdint.h>
#include <stdbool.h>
#include <stddef.h>
#ifdef __cplusplus
extern "C" {
#endif // __cplusplus
// ============================================================================
//
// Atomic built-ins
//
// ============================================================================
#ifdef __GNUC__
// GCC-compatible compiler: use built-in atomic operations
#define recorder_ring_fetch_add(Value, Offset) \
__atomic_fetch_add(&Value, Offset, __ATOMIC_ACQUIRE)
#define recorder_ring_add_fetch(Value, Offset) \
__atomic_add_fetch(&Value, Offset, __ATOMIC_ACQUIRE)
#define recorder_ring_compare_exchange(Value, Expected, New) \
__atomic_compare_exchange_n(&Value, &Expected, New, \
0, __ATOMIC_RELEASE, __ATOMIC_RELAXED)
#define RECORDER_RING_MAYBE_UNUSED __attribute__((unused))
#else // ! __GNUC__
#warning "Compiler not supported yet"
#define recorder_ring_fetch_add(Value, Offset) (Value += Offset)
#define recorder_ring_add_fetch(Value, Offset) ((Value += Offset), Value)
#define recorder_ring_compare_exchange(Val, Exp, New) ((Val = New), true)
#define RECORDER_RING_MAYBE_UNUSED
#endif
// ============================================================================
//
// C-style ring buffer type
//
// ============================================================================
typedef uintptr_t ringidx_t;
typedef struct recorder_ring
// ----------------------------------------------------------------------------
// Header for ring buffers
// ----------------------------------------------------------------------------
{
size_t size; // Number of elements in data array
size_t item_size; // Size of the elements
ringidx_t reader; // Reader index
ringidx_t writer; // Writer index
ringidx_t commit; // Last commited write
ringidx_t overflow; // Overflowed writes
} recorder_ring_t, *recorder_ring_p;
/* Deal with blocking situations on given ring
- Return true if situation is handled and operation can proceed
- Return false will abort read or write operation.
- May be NULL to implement default non-blocking mode
The functions take from/to as argument bys design, because the
corresponding values may have been changed in the ring
by the time the block-handling function get to read them. */
typedef bool (*recorder_ring_block_fn)(recorder_ring_p,
ringidx_t from, ringidx_t to);
extern recorder_ring_p recorder_ring_init(recorder_ring_p ring,
size_t size, size_t item_size);
extern recorder_ring_p recorder_ring_new(size_t size, size_t item_size);
extern void recorder_ring_delete(recorder_ring_p ring);
extern size_t recorder_ring_readable(recorder_ring_p ring, ringidx_t *reader);
extern size_t recorder_ring_writable(recorder_ring_p ring);
extern size_t recorder_ring_read(recorder_ring_p ring,
void *data, size_t count,
ringidx_t *reader,
recorder_ring_block_fn read_block,
recorder_ring_block_fn read_overflow);
extern void * recorder_ring_peek(recorder_ring_p ring);
extern ringidx_t recorder_ring_write(recorder_ring_p ring,
const void *data, size_t count,
recorder_ring_block_fn write_block,
recorder_ring_block_fn commit_block,
ringidx_t *writer);
#define RECORDER_RING_TYPE_DECLARE(Ring, Type) \
/* ----------------------------------------------------------------*/ \
/* Declare a ring buffer type with Size elements of given Type */ \
/* ----------------------------------------------------------------*/ \
\
typedef struct Ring \
{ \
recorder_ring_t ring; \
Type data[0]; \
} Ring; \
\
typedef bool (*Ring##_block_fn)(Ring *,ringidx_t, ringidx_t); \
\
static inline RECORDER_RING_MAYBE_UNUSED \
Ring *Ring##_new(size_t size) \
{ \
return (Ring *) recorder_ring_new(size, sizeof(Type)); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
void Ring##_delete(Ring *rb) \
{ \
recorder_ring_delete(&rb->ring); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
Type * Ring##_peek(Ring *rb) \
{ \
return (Type *) recorder_ring_peek(&rb->ring); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
size_t Ring##_read(Ring *rb, \
Type *ptr, \
size_t count, \
ringidx_t *reader, \
Ring##_block_fn block, \
Ring##_block_fn overflow) \
{ \
return recorder_ring_read(&rb->ring, ptr, count, reader, \
(recorder_ring_block_fn) block, \
(recorder_ring_block_fn) overflow); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
size_t Ring##_write(Ring *rb, \
Type *ptr, \
size_t count, \
Ring##_block_fn wrblk, \
Ring##_block_fn cmblk, \
ringidx_t *writer) \
{ \
return recorder_ring_write(&rb->ring, ptr, count, \
(recorder_ring_block_fn) wrblk, \
(recorder_ring_block_fn) cmblk, \
writer); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
ringidx_t Ring##_readable(Ring *rb) \
{ \
return recorder_ring_readable(&rb->ring); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
ringidx_t Ring##_writable(Ring *rb) \
{ \
return recorder_ring_writable(&rb->ring); \
}
// ============================================================================
//
// Static ring buffer allocation
//
// ============================================================================
#define RECORDER_RING_DECLARE(Name, Type, Size) \
/* ----------------------------------------------------------------*/ \
/* Declare a named ring buffer with helper functions to access it */ \
/* ----------------------------------------------------------------*/ \
/* This is what you should use in headers */ \
\
extern struct Name##_ring \
{ \
recorder_ring_t ring; \
Type data[Size]; \
} Name; \
\
static inline RECORDER_RING_MAYBE_UNUSED \
size_t Name##_readable() \
{ \
return recorder_ring_readable(&Name.ring, NULL); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
size_t Name##_writable() \
{ \
return recorder_ring_writable(&Name.ring); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
Type * Name##_peek() \
{ \
return (Type *) recorder_ring_peek(&Name.ring); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
size_t Name##_read(Type *ptr, ringidx_t count) \
{ \
return recorder_ring_read(&Name.ring, ptr, count, \
NULL, NULL, NULL); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
size_t Name##_write(Type *ptr, ringidx_t count) \
{ \
return recorder_ring_write(&Name.ring, ptr, count, \
NULL, NULL, NULL); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
size_t Name##_block_read(Type *ptr, \
size_t count, \
ringidx_t *reader, \
recorder_ring_block_fn block, \
recorder_ring_block_fn overflow) \
{ \
return recorder_ring_read(&Name.ring, ptr, count, \
reader, block, overflow); \
} \
\
static inline RECORDER_RING_MAYBE_UNUSED \
size_t Name##_block_write(const Type *ptr, \
size_t count, \
recorder_ring_block_fn write_block, \
recorder_ring_block_fn commit_block, \
ringidx_t *pos) \
{ \
return recorder_ring_write(&Name.ring, ptr, count, \
write_block, commit_block, pos); \
}
#define RECORDER_RING_DEFINE(Name, Type, Size) \
/* ----------------------------------------------------------------*/ \
/* Define a named ring buffer */ \
/* ----------------------------------------------------------------*/ \
\
struct Name##_ring Name = \
{ \
{ Size, sizeof(Type), 0, 0, 0, 0 } \
};
#ifdef __cplusplus
}
#endif // __cplusplus
#endif // RECORDER_RING_H
|
