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Modify MPMCQueue behaviour to use i32 over isize; Correct cache line padding within MPMCQueue

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This commit is contained in:
gingerBill
2021-07-28 00:59:30 +01:00
parent 541c79c01a
commit af32aba7fc
2 changed files with 46 additions and 35 deletions
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67
src/queue.cpp
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@@ -1,40 +1,41 @@
template <typename T>
struct MPMCQueueNode {
std::atomic<isize> idx;
T data;
std::atomic<i32> idx;
T data;
};
template <typename T>
struct MPMCQueueNodeNonAtomic {
isize idx;
T data;
i32 idx;
T data;
};
typedef char CacheLinePad[64];
// Multiple Producer Multiple Consumer Queue
template <typename T>
struct MPMCQueue {
CacheLinePad pad0;
isize mask;
static size_t const PAD0_OFFSET = (sizeof(i32) + sizeof(Array<MPMCQueueNode<T>>) + sizeof(BlockingMutex) + sizeof(i32));
i32 mask;
Array<MPMCQueueNode<T>> buffer;
BlockingMutex mutex;
std::atomic<isize> count;
std::atomic<i32> count;
CacheLinePad pad1;
std::atomic<isize> head_idx;
char pad0[(128 - PAD0_OFFSET) % 64];
std::atomic<i32> head_idx;
CacheLinePad pad2;
std::atomic<isize> tail_idx;
CacheLinePad pad3;
char pad1[64 - sizeof(i32)];
std::atomic<i32> tail_idx;
};
template <typename T>
void mpmc_init(MPMCQueue<T> *q, gbAllocator a, isize size) {
size = gb_max(size, 8);
size = next_pow2_isize(size);
void mpmc_init(MPMCQueue<T> *q, gbAllocator a, isize size_i) {
if (size_i < 8) {
size_i = 8;
}
GB_ASSERT(size_i < I32_MAX);
i32 size = cast(i32)size_i;
size = next_pow2(size);
GB_ASSERT(gb_is_power_of_two(size));
mutex_init(&q->mutex);
@@ -43,7 +44,7 @@ void mpmc_init(MPMCQueue<T> *q, gbAllocator a, isize size) {
// NOTE(bill): pretend it's not atomic for performance
auto *raw_data = cast(MPMCQueueNodeNonAtomic<T> *)q->buffer.data;
for (isize i = 0; i < size; i += 8) {
for (i32 i = 0; i < size; i += 8) {
raw_data[i+0].idx = i+0;
raw_data[i+1].idx = i+1;
raw_data[i+2].idx = i+2;
@@ -63,20 +64,18 @@ void mpmc_destroy(MPMCQueue<T> *q) {
template <typename T>
isize mpmc_enqueue(MPMCQueue<T> *q, T const &data) {
if (q->mask == 0) {
return -1;
}
i32 mpmc_enqueue(MPMCQueue<T> *q, T const &data) {
GB_ASSERT(q->mask != 0);
isize head_idx = q->head_idx.load(std::memory_order_relaxed);
i32 head_idx = q->head_idx.load(std::memory_order_relaxed);
for (;;) {
auto node = &q->buffer.data[head_idx & q->mask];
isize node_idx = node->idx.load(std::memory_order_acquire);
isize diff = node_idx - head_idx;
i32 node_idx = node->idx.load(std::memory_order_acquire);
i32 diff = node_idx - head_idx;
if (diff == 0) {
isize next_head_idx = head_idx+1;
i32 next_head_idx = head_idx+1;
if (q->head_idx.compare_exchange_weak(head_idx, next_head_idx)) {
node->data = data;
node->idx.store(next_head_idx, std::memory_order_release);
@@ -84,8 +83,8 @@ isize mpmc_enqueue(MPMCQueue<T> *q, T const &data) {
}
} else if (diff < 0) {
mutex_lock(&q->mutex);
isize old_size = q->buffer.count;
isize new_size = old_size*2;
i32 old_size = cast(i32)q->buffer.count;
i32 new_size = old_size*2;
array_resize(&q->buffer, new_size);
if (q->buffer.data == nullptr) {
GB_PANIC("Unable to resize enqueue: %td -> %td", old_size, new_size);
@@ -94,7 +93,7 @@ isize mpmc_enqueue(MPMCQueue<T> *q, T const &data) {
}
// NOTE(bill): pretend it's not atomic for performance
auto *raw_data = cast(MPMCQueueNodeNonAtomic<T> *)q->buffer.data;
for (isize i = old_size; i < new_size; i++) {
for (i32 i = old_size; i < new_size; i++) {
raw_data[i].idx = i;
}
q->mask = new_size-1;
@@ -111,15 +110,15 @@ bool mpmc_dequeue(MPMCQueue<T> *q, T *data_) {
return false;
}
isize tail_idx = q->tail_idx.load(std::memory_order_relaxed);
i32 tail_idx = q->tail_idx.load(std::memory_order_relaxed);
for (;;) {
auto node = &q->buffer.data[tail_idx & q->mask];
isize node_idx = node->idx.load(std::memory_order_acquire);
isize diff = node_idx - (tail_idx+1);
i32 node_idx = node->idx.load(std::memory_order_acquire);
i32 diff = node_idx - (tail_idx+1);
if (diff == 0) {
isize next_tail_idx = tail_idx+1;
i32 next_tail_idx = tail_idx+1;
if (q->tail_idx.compare_exchange_weak(tail_idx, next_tail_idx)) {
if (data_) *data_ = node->data;
node->idx.store(tail_idx + q->mask + 1, std::memory_order_release);