diff options
| -rw-r--r-- | src/ring.c | 78 |
1 files changed, 53 insertions, 25 deletions
@@ -1,4 +1,4 @@ -// Copyright 2011-2020 David Robillard <d@drobilla.net> +// Copyright 2011-2022 David Robillard <d@drobilla.net> // SPDX-License-Identifier: ISC #include "zix/ring.h" @@ -19,17 +19,13 @@ # define ZIX_MLOCK(ptr, size) #endif +/* + Note that for simplicity, only x86 and x64 are supported with MSVC. Hopefully + stdatomic.h support arrives before anyone cares about running this code on + Windows on ARM. +*/ #if defined(_MSC_VER) -# include <windows.h> -# define ZIX_READ_BARRIER() MemoryBarrier() -# define ZIX_WRITE_BARRIER() MemoryBarrier() -#elif defined(__GNUC__) -# define ZIX_READ_BARRIER() __atomic_thread_fence(__ATOMIC_ACQUIRE) -# define ZIX_WRITE_BARRIER() __atomic_thread_fence(__ATOMIC_RELEASE) -#else -# pragma message("warning: No memory barriers, possible SMP bugs") -# define ZIX_READ_BARRIER() -# define ZIX_WRITE_BARRIER() +# include <intrin.h> #endif struct ZixRingImpl { @@ -42,6 +38,30 @@ struct ZixRingImpl { }; static inline uint32_t +zix_atomic_load(const uint32_t* const ptr) +{ +#if defined(_MSC_VER) + const uint32_t val = *ptr; + _ReadBarrier(); + return val; +#else + return __atomic_load_n(ptr, __ATOMIC_ACQUIRE); +#endif +} + +static inline void +zix_atomic_store(uint32_t* const ptr, // NOLINT(readability-non-const-parameter) + const uint32_t val) +{ +#if defined(_MSC_VER) + _WriteBarrier(); + *ptr = val; +#else + __atomic_store_n(ptr, val, __ATOMIC_RELEASE); +#endif +} + +static inline uint32_t next_power_of_two(uint32_t size) { // http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2 @@ -99,6 +119,12 @@ zix_ring_reset(ZixRing* ring) ring->read_head = 0; } +/* + General pattern for public thread-safe functions below: start with a single + atomic load of the "other's" index, then do whatever work, and finally end + with a single atomic store to "your" index (if it is changed). +*/ + static inline uint32_t read_space_internal(const ZixRing* ring, uint32_t r, uint32_t w) { @@ -108,7 +134,9 @@ read_space_internal(const ZixRing* ring, uint32_t r, uint32_t w) uint32_t zix_ring_read_space(const ZixRing* ring) { - return read_space_internal(ring, ring->read_head, ring->write_head); + const uint32_t w = zix_atomic_load(&ring->write_head); + + return read_space_internal(ring, ring->read_head, w); } static inline uint32_t @@ -120,7 +148,9 @@ write_space_internal(const ZixRing* ring, uint32_t r, uint32_t w) uint32_t zix_ring_write_space(const ZixRing* ring) { - return write_space_internal(ring, ring->read_head, ring->write_head); + const uint32_t r = zix_atomic_load(&ring->read_head); + + return write_space_internal(ring, r, ring->write_head); } uint32_t @@ -154,41 +184,41 @@ peek_internal(const ZixRing* ring, uint32_t zix_ring_peek(ZixRing* ring, void* dst, uint32_t size) { - return peek_internal(ring, ring->read_head, ring->write_head, size, dst); + const uint32_t w = zix_atomic_load(&ring->write_head); + + return peek_internal(ring, ring->read_head, w, size, dst); } uint32_t zix_ring_read(ZixRing* ring, void* dst, uint32_t size) { + const uint32_t w = zix_atomic_load(&ring->write_head); const uint32_t r = ring->read_head; - const uint32_t w = ring->write_head; if (!peek_internal(ring, r, w, size, dst)) { return 0; } - ZIX_READ_BARRIER(); - ring->read_head = (r + size) & ring->size_mask; + zix_atomic_store(&ring->read_head, (r + size) & ring->size_mask); return size; } uint32_t zix_ring_skip(ZixRing* ring, uint32_t size) { + const uint32_t w = zix_atomic_load(&ring->write_head); const uint32_t r = ring->read_head; - const uint32_t w = ring->write_head; if (read_space_internal(ring, r, w) < size) { return 0; } - ZIX_READ_BARRIER(); - ring->read_head = (r + size) & ring->size_mask; + zix_atomic_store(&ring->read_head, (r + size) & ring->size_mask); return size; } uint32_t zix_ring_write(ZixRing* ring, const void* src, uint32_t size) { - const uint32_t r = ring->read_head; + const uint32_t r = zix_atomic_load(&ring->read_head); const uint32_t w = ring->write_head; if (write_space_internal(ring, r, w) < size) { return 0; @@ -197,15 +227,13 @@ zix_ring_write(ZixRing* ring, const void* src, uint32_t size) const uint32_t end = w + size; if (end <= ring->size) { memcpy(&ring->buf[w], src, size); - ZIX_WRITE_BARRIER(); - ring->write_head = end & ring->size_mask; + zix_atomic_store(&ring->write_head, end & ring->size_mask); } else { const uint32_t size1 = ring->size - w; const uint32_t size2 = size - size1; memcpy(&ring->buf[w], src, size1); memcpy(&ring->buf[0], (const char*)src + size1, size2); - ZIX_WRITE_BARRIER(); - ring->write_head = size2; + zix_atomic_store(&ring->write_head, size2); } return size; |