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move to work-stealing threadpool

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This commit is contained in:
Colin Davidson
2022-12-28 21:44:17 -08:00
parent 00823ca88c
commit 5f27f2dd7f
4 changed files with 298 additions and 166 deletions
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258
src/thread_pool.cpp
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@@ -3,164 +3,198 @@
struct WorkerTask;
struct ThreadPool;
#define WORKER_TASK_PROC(name) isize name(void *data)
typedef WORKER_TASK_PROC(WorkerTaskProc);
gb_thread_local Thread *current_thread;
gb_internal void thread_pool_init(ThreadPool *pool, gbAllocator const &a, isize thread_count, char const *worker_name);
gb_internal void thread_pool_destroy(ThreadPool *pool);
gb_internal bool thread_pool_add_task(ThreadPool *pool, WorkerTaskProc *proc, void *data);
gb_internal void thread_pool_wait(ThreadPool *pool);
struct WorkerTask {
WorkerTask * next;
WorkerTaskProc *do_work;
void * data;
ThreadPool * pool;
};
struct ThreadPool {
gbAllocator allocator;
BlockingMutex mutex;
Condition task_cond;
Slice<Thread> threads;
WorkerTask *task_queue;
std::atomic<isize> ready;
std::atomic<bool> stop;
std::atomic<bool> running;
BlockingMutex task_lock;
Condition tasks_available;
Futex tasks_left;
};
gb_internal THREAD_PROC(thread_pool_thread_proc);
gb_internal void thread_pool_init(ThreadPool *pool, gbAllocator const &a, isize thread_count, char const *worker_name) {
mutex_init(&pool->task_lock);
condition_init(&pool->tasks_available);
pool->allocator = a;
pool->stop = false;
mutex_init(&pool->mutex);
condition_init(&pool->task_cond);
slice_init(&pool->threads, a, thread_count);
for_array(i, pool->threads) {
slice_init(&pool->threads, a, thread_count + 1);
// setup the main thread
thread_init(pool, &pool->threads[0], 0);
current_thread = &pool->threads[0];
for_array_off(i, 1, pool->threads) {
Thread *t = &pool->threads[i];
thread_init_and_start(t, thread_pool_thread_proc, pool);
thread_init_and_start(pool, t, i);
}
pool->running = true;
}
gb_internal void thread_pool_destroy(ThreadPool *pool) {
mutex_lock(&pool->mutex);
pool->stop = true;
condition_broadcast(&pool->task_cond);
mutex_unlock(&pool->mutex);
pool->running = false;
for_array(i, pool->threads) {
for_array_off(i, 1, pool->threads) {
Thread *t = &pool->threads[i];
condition_broadcast(&pool->tasks_available);
thread_join_and_destroy(t);
}
for_array(i, pool->threads) {
free(pool->threads[i].queue);
}
gb_free(pool->allocator, pool->threads.data);
mutex_destroy(&pool->mutex);
condition_destroy(&pool->task_cond);
mutex_destroy(&pool->task_lock);
condition_destroy(&pool->tasks_available);
}
gb_internal bool thread_pool_queue_empty(ThreadPool *pool) {
return pool->task_queue == nullptr;
void thread_pool_queue_push(Thread *thread, WorkerTask task) {
uint64_t capture;
uint64_t new_capture;
do {
capture = thread->head_and_tail.load();
uint64_t mask = thread->capacity - 1;
uint64_t head = (capture >> 32) & mask;
uint64_t tail = ((uint32_t)capture) & mask;
uint64_t new_head = (head + 1) & mask;
if (new_head == tail) {
GB_PANIC("Thread Queue Full!\n");
}
// This *must* be done in here, to avoid a potential race condition where we no longer own the slot by the time we're assigning
thread->queue[head] = task;
new_capture = (new_head << 32) | tail;
} while (!thread->head_and_tail.compare_exchange_weak(capture, new_capture));
thread->pool->tasks_left.fetch_add(1);
condition_broadcast(&thread->pool->tasks_available);
}
gb_internal WorkerTask *thread_pool_queue_pop(ThreadPool *pool) {
GB_ASSERT(pool->task_queue != nullptr);
WorkerTask *task = pool->task_queue;
pool->task_queue = task->next;
return task;
}
gb_internal void thread_pool_queue_push(ThreadPool *pool, WorkerTask *task) {
GB_ASSERT(task != nullptr);
task->next = pool->task_queue;
pool->task_queue = task;
bool thread_pool_queue_pop(Thread *thread, WorkerTask *task) {
uint64_t capture;
uint64_t new_capture;
do {
capture = thread->head_and_tail.load();
uint64_t mask = thread->capacity - 1;
uint64_t head = (capture >> 32) & mask;
uint64_t tail = ((uint32_t)capture) & mask;
uint64_t new_tail = (tail + 1) & mask;
if (tail == head) {
return false;
}
// Making a copy of the task before we increment the tail, avoiding the same potential race condition as above
*task = thread->queue[tail];
new_capture = (head << 32) | new_tail;
} while (!thread->head_and_tail.compare_exchange_weak(capture, new_capture));
return true;
}
gb_internal bool thread_pool_add_task(ThreadPool *pool, WorkerTaskProc *proc, void *data) {
GB_ASSERT(proc != nullptr);
WorkerTask *task = gb_alloc_item(permanent_allocator(), WorkerTask);
if (task == nullptr) {
GB_PANIC("Out of memory");
return false;
}
task->pool = pool;
task->do_work = proc;
task->data = data;
WorkerTask task = {};
task.do_work = proc;
task.data = data;
mutex_lock(&pool->mutex);
thread_pool_queue_push(pool, task);
GB_ASSERT(pool->ready >= 0);
pool->ready.fetch_add(1);
condition_broadcast(&pool->task_cond);
mutex_unlock(&pool->mutex);
thread_pool_queue_push(current_thread, task);
return true;
}
gb_internal void thread_pool_do_task(WorkerTask *task) {
task->do_work(task->data);
}
gb_internal void thread_pool_wait(ThreadPool *pool) {
if (pool->threads.count == 0) {
while (!thread_pool_queue_empty(pool)) {
thread_pool_do_task(thread_pool_queue_pop(pool));
pool->ready.fetch_sub(1);
}
GB_ASSERT(pool->ready == 0);
return;
}
for (;;) {
mutex_lock(&pool->mutex);
WorkerTask task;
while (!pool->stop && pool->ready > 0 && thread_pool_queue_empty(pool)) {
condition_wait(&pool->task_cond, &pool->mutex);
}
if ((pool->stop || pool->ready == 0) && thread_pool_queue_empty(pool)) {
mutex_unlock(&pool->mutex);
return;
while (pool->tasks_left) {
// if we've got tasks on our queue, run them
while (thread_pool_queue_pop(current_thread, &task)) {
task.do_work(task.data);
pool->tasks_left.fetch_sub(1);
}
WorkerTask *task = thread_pool_queue_pop(pool);
mutex_unlock(&pool->mutex);
thread_pool_do_task(task);
if (--pool->ready == 0) {
mutex_lock(&pool->mutex);
condition_broadcast(&pool->task_cond);
mutex_unlock(&pool->mutex);
// is this mem-barriered enough?
// This *must* be executed in this order, so the futex wakes immediately
// if rem_tasks has changed since we checked last, otherwise the program
// will permanently sleep
Footex rem_tasks = pool->tasks_left.load();
if (!rem_tasks) {
break;
}
tpool_wait_on_addr(&pool->tasks_left, rem_tasks);
}
}
gb_internal THREAD_PROC(thread_pool_thread_proc) {
ThreadPool *pool = cast(ThreadPool *)thread->user_data;
WorkerTask task;
current_thread = thread;
ThreadPool *pool = current_thread->pool;
for (;;) {
mutex_lock(&pool->mutex);
while (!pool->stop && thread_pool_queue_empty(pool)) {
condition_wait(&pool->task_cond, &pool->mutex);
}
if (pool->stop && thread_pool_queue_empty(pool)) {
mutex_unlock(&pool->mutex);
return 0;
work_start:
if (!pool->running) {
break;
}
WorkerTask *task = thread_pool_queue_pop(pool);
mutex_unlock(&pool->mutex);
thread_pool_do_task(task);
if (--pool->ready == 0) {
mutex_lock(&pool->mutex);
condition_broadcast(&pool->task_cond);
mutex_unlock(&pool->mutex);
// If we've got tasks to process, work through them
size_t finished_tasks = 0;
while (thread_pool_queue_pop(current_thread, &task)) {
task.do_work(task.data);
pool->tasks_left.fetch_sub(1);
finished_tasks += 1;
}
if (finished_tasks > 0 && !pool->tasks_left) {
tpool_wake_addr(&pool->tasks_left);
}
// If there's still work somewhere and we don't have it, steal it
if (pool->tasks_left) {
isize idx = current_thread->idx;
for_array(i, pool->threads) {
if (!pool->tasks_left) {
break;
}
idx = (idx + 1) % pool->threads.count;
Thread *thread = &pool->threads[idx];
WorkerTask task;
if (!thread_pool_queue_pop(thread, &task)) {
continue;
}
task.do_work(task.data);
pool->tasks_left.fetch_sub(1);
if (!pool->tasks_left) {
tpool_wake_addr(&pool->tasks_left);
}
goto work_start;
}
}
// if we've done all our work, and there's nothing to steal, go to sleep
mutex_lock(&pool->task_lock);
condition_wait(&pool->tasks_available, &pool->task_lock);
mutex_unlock(&pool->task_lock);
}
}
return 0;
}