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#include <torch/csrc/lazy/core/thread_pool.h>
#include <c10/util/Logging.h>
#include <c10/util/irange.h>
#include <torch/csrc/lazy/core/config.h>
#include <torch/csrc/lazy/core/metrics.h>
#include <condition_variable>
#include <deque>
#include <exception>
#include <mutex>
namespace torch {
namespace lazy {
namespace {
class ThreadPool {
public:
explicit ThreadPool(size_t num_threads) {
threads_.reserve(num_threads);
for (const auto i : c10::irange(num_threads)) {
(void)i; // Suppress unused variable warning
threads_.emplace_back([this]() { Worker(); });
}
}
~ThreadPool() {
{
std::lock_guard<std::mutex> lock(mutex_);
exiting_ = true;
cv_.notify_all();
}
for (auto& thread : threads_) {
thread.join();
}
}
void Schedule(std::function<void()> closure) {
// If we have more work scheduled than waiting worker threads, just schedule
// it on a separate thread. This prevents tricky thread-pool-size-deadlocks
// caused by an undersized thread pool and closures that end up doing sync
// waits on the pool threads.
bool scheduled = false;
{
std::lock_guard<std::mutex> lock(mutex_);
if (work_.size() < waiting_) {
work_.emplace_back(std::move(closure));
scheduled = true;
}
}
if (scheduled) {
cv_.notify_one();
} else {
// NOLINTNEXTLINE(bugprone-use-after-move)
ScheduleOnThread(std::move(closure));
}
}
private:
void Worker() {
while (true) {
std::function<void()> closure = GetWork();
if (closure == nullptr) {
break;
}
try {
closure();
} catch (const std::exception& ex) {
TORCH_LAZY_COUNTER("ThreadPoolException", 1);
LOG(ERROR) << "Exception from running thread pool closure: "
<< ex.what();
}
}
}
void ScheduleOnThread(std::function<void()> closure) {
std::thread thread(std::move(closure));
thread.detach();
}
std::function<void()> GetWork() {
std::unique_lock<std::mutex> lock(mutex_);
++waiting_;
cv_.wait(lock, [this] { return exiting_ || !work_.empty(); });
--waiting_;
if (work_.empty()) {
return nullptr;
}
std::function<void()> closure(std::move(work_.front()));
work_.pop_front();
return closure;
}
std::vector<std::thread> threads_;
std::mutex mutex_;
std::condition_variable cv_;
bool exiting_ = false;
std::deque<std::function<void()>> work_;
size_t waiting_ = 0;
};
ThreadPool* GetIoThreadPool() {
static ThreadPool* pool =
new ThreadPool(FLAGS_torch_lazy_io_thread_pool_size);
return pool;
}
} // namespace
class Completion::Data {
public:
void Wait() {
std::unique_lock<std::mutex> lock(mutex_);
cv_.wait(lock, [this] { return completed_; });
if (exptr_ != nullptr) {
std::rethrow_exception(exptr_);
}
}
static std::function<void()> GetCompleter(
std::shared_ptr<Data> data,
std::function<void()> closure) {
auto closure_wrapper = [closure = std::move(closure), data]() {
std::exception_ptr exptr;
try {
closure();
} catch (...) {
exptr = std::current_exception();
}
data->Complete(exptr);
};
return closure_wrapper;
}
private:
void Complete(std::exception_ptr exptr) {
std::lock_guard<std::mutex> lock(mutex_);
exptr_ = std::move(exptr);
completed_ = true;
cv_.notify_all();
}
std::mutex mutex_;
std::condition_variable cv_;
bool completed_ = false;
std::exception_ptr exptr_;
};
Completion::Completion(std::shared_ptr<Data> data) : data_(std::move(data)) {}
void Completion::Wait() {
data_->Wait();
}
void ScheduleIoClosure(std::function<void()> closure) {
GetIoThreadPool()->Schedule(std::move(closure));
}
Completion ScheduleIoClosureWithCompletion(std::function<void()> closure) {
auto data = std::make_shared<Completion::Data>();
GetIoThreadPool()->Schedule(
Completion::Data::GetCompleter(data, std::move(closure)));
return Completion(std::move(data));
}
} // namespace lazy
} // namespace torch
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