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ParallelNative.cpp
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ParallelNative.cpp
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#if AT_PARALLEL_NATIVE
#include <ATen/Parallel.h>
#include <ATen/PTThreadPool.h>
#ifndef C10_MOBILE
#include <c10/core/thread_pool.h>
#else
#include <caffe2/utils/threadpool/ThreadPool.h>
#include <caffe2/utils/threadpool/ThreadPoolMobile.h>
#endif // C10_MOBILE
#include <atomic>
#ifdef _OPENMP
#include <omp.h>
#endif
#ifdef TH_BLAS_MKL
#include <mkl.h>
#endif
namespace at {
namespace {
// used with _set_in_parallel_region to mark master thread
// as in parallel region while executing parallel primitives
thread_local bool in_parallel_region_ = false;
// thread number (task_id) set by parallel primitive
thread_local size_t thread_num_ = 0;
void _set_in_parallel_region(bool in_region) {
in_parallel_region_ = in_region;
}
void _set_thread_num(size_t thread_num) {
thread_num_ = thread_num;
}
void _unset_thread_num() {
thread_num_ = 0;
}
#ifndef C10_MOBILE
const int NOT_SET = -1;
const int CONSUMED = -2;
// Number of threads set by the user
// NOT_SET -> positive value -> CONSUMED
// or
// NOT_SET -> CONSUMED
// Meaning:
// - NOT_SET - pool not initialized, user value is not set
// - positive value - pool not initialized, user value set
// - CONSUMED - pool is initialized
std::atomic<int> num_intraop_threads{NOT_SET};
int _num_pool_threads(int nthreads) {
if (nthreads == NOT_SET) {
nthreads = intraop_default_num_threads();
} else {
TORCH_INTERNAL_ASSERT(nthreads > 0);
}
// minus one because of the master thread
return nthreads - 1;
}
TaskThreadPoolBase& _get_intraop_pool() {
static std::shared_ptr<TaskThreadPoolBase> pool =
ThreadPoolRegistry()->Create(
"C10",
/* device_id */ 0,
/* pool_size */ _num_pool_threads(num_intraop_threads.exchange(CONSUMED)),
/* create_new */ true); // create a separate thread pool for intra-op
return *pool;
}
#endif // C10_MOBILE
// Run lambda function `fn` over `task_id` in [0, `range`) with threadpool.
// `fn` will be called with params: (thread_pool_task_id, task_id).
void _run_with_pool(const std::function<void(int, size_t)>& fn, size_t range) {
#ifndef C10_MOBILE
for (size_t i = 1; i < range; ++i) {
_get_intraop_pool().run([fn, i]() { fn((int)i, i); });
}
// Run the first task on the current thread directly.
fn(0, 0);
#else
caffe2::ThreadPool* pool = caffe2::mobile_threadpool();
if (pool) {
// caffe2::ThreadPool can utilize the current thread.
pool->run(fn, range);
} else {
for (size_t i = 0; i < range; ++i) {
fn(0, i);
}
}
#endif // C10_MOBILE
}
// RAII guard helps to support in_parallel_region() and get_thread_num() API.
struct ParallelRegionGuard {
ParallelRegionGuard(int64_t task_id) {
_set_thread_num(task_id);
_set_in_parallel_region(true);
}
~ParallelRegionGuard() {
_set_in_parallel_region(false);
_unset_thread_num();
}
};
} // namespace
namespace internal {
void _parallel_run(
const int64_t begin,
const int64_t end,
const int64_t grain_size,
const std::function<void(int64_t, int64_t, size_t)>& f) {
size_t num_tasks, chunk_size;
std::tie(num_tasks, chunk_size) =
internal::calc_num_tasks_and_chunk_size(begin, end, grain_size);
std::atomic_flag err_flag = ATOMIC_FLAG_INIT;
std::exception_ptr eptr;
std::vector<std::shared_ptr<c10::ivalue::Future>> futures(num_tasks);
for (size_t task_id = 0; task_id < num_tasks; ++task_id) {
futures[task_id] = std::make_shared<c10::ivalue::Future>(c10::NoneType::get());
}
auto task = [f, &eptr, &err_flag, &futures, begin, end, chunk_size]
(int /* unused */, size_t task_id) {
int64_t local_start = begin + task_id * chunk_size;
if (local_start < end) {
int64_t local_end = std::min(end, (int64_t)(chunk_size + local_start));
try {
ParallelRegionGuard guard(task_id);
f(local_start, local_end, task_id);
} catch (...) {
if (!err_flag.test_and_set()) {
eptr = std::current_exception();
}
}
}
futures[task_id]->markCompleted();
};
_run_with_pool(task, num_tasks);
// Wait for all tasks to finish.
for (size_t task_id = 0; task_id < num_tasks; ++task_id) {
futures[task_id]->wait();
}
if (eptr) {
std::rethrow_exception(eptr);
}
}
} // namespace internal
void init_num_threads() {
#ifdef _OPENMP
omp_set_num_threads(1);
#endif
#ifdef TH_BLAS_MKL
mkl_set_num_threads(1);
#endif
#ifdef C10_MOBILE
caffe2::mobile_threadpool();
#endif
}
void set_num_threads(int nthreads) {
#ifndef C10_MOBILE
TORCH_CHECK(nthreads > 0, "Expected positive number of threads");
int no_value = NOT_SET;
TORCH_CHECK(num_intraop_threads.compare_exchange_strong(no_value, nthreads),
"Error: cannot set number of interop threads "
"after parallel work has started or after set_num_threads call");
#else
TORCH_CHECK(false, "set_num_threads is not supported for mobile.");
#endif // C10_MOBILE
}
int get_num_threads() {
#ifndef C10_MOBILE
// not initializing pool unnecessarily,
// because pool cannot be resized after initialization
int nthreads = num_intraop_threads.load();
if (nthreads > 0) {
return nthreads;
} else if (nthreads == NOT_SET) {
return intraop_default_num_threads();
} else {
TORCH_INTERNAL_ASSERT(nthreads == CONSUMED);
return _get_intraop_pool().size() + 1;
}
#else
caffe2::ThreadPool* pool = caffe2::mobile_threadpool();
// caffe2::ThreadPool::getNumThreads() counts the current thread.
return !pool ? 1 /* current thread */ : pool->getNumThreads();
#endif // C10_MOBILE
}
int get_thread_num() {
return thread_num_;
}
bool in_parallel_region() {
#ifndef C10_MOBILE
return in_parallel_region_ || (
num_intraop_threads.load() == CONSUMED &&
// Needed as intraop_launch() doesn't set in_parallel_region().
_get_intraop_pool().inThreadPool()
);
#else
return in_parallel_region_;
#endif // C10_MOBILE
}
void intraop_launch(std::function<void()> func) {
#ifndef C10_MOBILE
if (!in_parallel_region() && get_num_threads() > 1) {
_get_intraop_pool().run(func);
} else {
// execute inline if we're in parallel region
func();
}
#else
// TODO: caffe2::ThreadPool doesn't support submitting tasks separately and
// running in parallel. Should fix it when this API becomes popular.
func();
#endif // C10_MOBILE
}
std::shared_ptr<c10::ivalue::Future> intraop_launch_future(
std::function<void()> func) {
#ifndef C10_MOBILE
auto future = std::make_shared<c10::ivalue::Future>(c10::NoneType::get());
if (!in_parallel_region() && get_num_threads() > 1) {
_get_intraop_pool().run(
[func, future]() {
func();
future->markCompleted();
}
);
} else {
func();
future->markCompleted();
}
return future;
#else
// TODO: caffe2::ThreadPool doesn't support submitting tasks separately and
// running in parallel. Should fix it when this API becomes popular.
auto future = std::make_shared<c10::ivalue::Future>(NoneType::get());
func();
future->markCompleted();
return future;
#endif // C10_MOBILE
}
} // namespace at
#endif