mediapipe/mediapipe/framework/deps/threadpool_pthread_impl.cc

// Copyright 2019 The MediaPipe Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include <errno.h>
#include <pthread.h>
#include <string.h>
#include <sys/syscall.h>
#include <unistd.h>

#include "absl/strings/str_cat.h"
#include "absl/strings/str_join.h"
#include "mediapipe/framework/deps/threadpool.h"
#include "mediapipe/framework/port/logging.h"

namespace mediapipe {

class ThreadPool::WorkerThread {
 public:
  // Creates and starts a thread that runs pool->RunWorker().
  WorkerThread(ThreadPool* pool, const std::string& name_prefix);

  // REQUIRES: Join() must have been called.
  ~WorkerThread();

  // Joins with the running thread.
  void Join();

 private:
  static void* ThreadBody(void* arg);

  ThreadPool* pool_;
  std::string name_prefix_;
  pthread_t thread_;
};

ThreadPool::WorkerThread::WorkerThread(ThreadPool* pool,
                                       const std::string& name_prefix)
    : pool_(pool), name_prefix_(name_prefix) {
  int res = pthread_create(&thread_, nullptr, ThreadBody, this);
  CHECK_EQ(res, 0) << "pthread_create failed";
}

ThreadPool::WorkerThread::~WorkerThread() {}

void ThreadPool::WorkerThread::Join() { pthread_join(thread_, nullptr); }

void* ThreadPool::WorkerThread::ThreadBody(void* arg) {
  auto thread = reinterpret_cast<WorkerThread*>(arg);
  int nice_priority_level =
      thread->pool_->thread_options().nice_priority_level();
  const std::set<int> selected_cpus = thread->pool_->thread_options().cpu_set();
#if defined(__linux__)
  const std::string name =
      internal::CreateThreadName(thread->name_prefix_, syscall(SYS_gettid));
  if (nice_priority_level != 0) {
    if (nice(nice_priority_level) != -1 || errno == 0) {
      VLOG(1) << "Changed the nice priority level by " << nice_priority_level;
    } else {
      LOG(ERROR) << "Error : " << strerror(errno) << std::endl
                 << "Could not change the nice priority level by "
                 << nice_priority_level;
    }
  }
  if (!selected_cpus.empty()) {
    cpu_set_t cpu_set;
    CPU_ZERO(&cpu_set);
    for (const int cpu : selected_cpus) {
      CPU_SET(cpu, &cpu_set);
    }
    if (sched_setaffinity(syscall(SYS_gettid), sizeof(cpu_set_t), &cpu_set) !=
            -1 ||
        errno == 0) {
      VLOG(1) << "Pinned the thread pool executor to processor "
              << absl::StrJoin(selected_cpus, ", processor ") << ".";
    } else {
      LOG(ERROR) << "Error : " << strerror(errno) << std::endl
                 << "Failed to set processor affinity. Ignore processor "
                    "affinity setting for now.";
    }
  }
  int error = pthread_setname_np(pthread_self(), name.c_str());
  if (error != 0) {
    LOG(ERROR) << "Error : " << strerror(error) << std::endl
               << "Failed to set name for thread: " << name;
  }
#else
  const std::string name = internal::CreateThreadName(thread->name_prefix_, 0);
  if (nice_priority_level != 0 || !selected_cpus.empty()) {
    LOG(ERROR) << "Thread priority and processor affinity feature aren't "
                  "supported on the current platform.";
  }
#if __APPLE__
  int error = pthread_setname_np(name.c_str());
  if (error != 0) {
    LOG(ERROR) << "Error : " << strerror(error) << std::endl
               << "Failed to set name for thread: " << name;
  }
#endif  // __APPLE__
#endif  // __linux__
  thread->pool_->RunWorker();
  return nullptr;
}

ThreadPool::ThreadPool(int num_threads) {
  num_threads_ = (num_threads == 0) ? 1 : num_threads;
}

ThreadPool::ThreadPool(const std::string& name_prefix, int num_threads)
    : name_prefix_(name_prefix) {
  num_threads_ = (num_threads == 0) ? 1 : num_threads;
}

ThreadPool::ThreadPool(const ThreadOptions& thread_options,
                       const std::string& name_prefix, int num_threads)
    : name_prefix_(name_prefix), thread_options_(thread_options) {
  num_threads_ = (num_threads == 0) ? 1 : num_threads;
}

ThreadPool::~ThreadPool() {
  mutex_.Lock();
  stopped_ = true;
  condition_.SignalAll();
  mutex_.Unlock();

  for (int i = 0; i < threads_.size(); ++i) {
    threads_[i]->Join();
    delete threads_[i];
  }

  threads_.clear();
}

void ThreadPool::StartWorkers() {
  for (int i = 0; i < num_threads_; ++i) {
    threads_.push_back(new WorkerThread(this, name_prefix_));
  }
}

void ThreadPool::Schedule(std::function<void()> callback) {
  mutex_.Lock();
  tasks_.push_back(std::move(callback));
  condition_.Signal();
  mutex_.Unlock();
}

int ThreadPool::num_threads() const { return num_threads_; }

void ThreadPool::RunWorker() {
  mutex_.Lock();
  while (true) {
    if (!tasks_.empty()) {
      std::function<void()> task = std::move(tasks_.front());
      tasks_.pop_front();
      mutex_.Unlock();
      task();
      mutex_.Lock();
    } else {
      if (stopped_) {
        break;
      } else {
        condition_.Wait(&mutex_);
      }
    }
  }
  mutex_.Unlock();
}

const ThreadOptions& ThreadPool::thread_options() const {
  return thread_options_;
}

namespace internal {

// TODO: revise this:
// - thread_id is not portable
// - the 16-byte limit is Linux-specific
// - the std::thread implementation has a copy of this but doesn't use it
// - why do we even need the thread id in the name? any thread list should show
//   the id too.
std::string CreateThreadName(const std::string& prefix, int thread_id) {
  std::string name = absl::StrCat(prefix, "/", thread_id);
  // 16 is the limit allowed by `pthread_setname_np`, including
  // the terminating null byte ('\0')
  constexpr size_t kMaxThreadNameLength = 15;
  name.resize(std::min(name.length(), kMaxThreadNameLength));
  return name;
}

}  // namespace internal

}  // namespace mediapipe