TaskPool.cpp revision 326949 
1//===--------------------- TaskPool.cpp -------------------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9
10#include "lldb/Host/TaskPool.h"
11#include "lldb/Host/ThreadLauncher.h"
12
13#include <cstdint> // for uint32_t
14#include <queue>   // for queue
15#include <thread>  // for thread
16
17namespace lldb_private {
18
19namespace {
20class TaskPoolImpl {
21public:
22  static TaskPoolImpl &GetInstance();
23
24  void AddTask(std::function<void()> &&task_fn);
25
26private:
27  TaskPoolImpl();
28
29  static lldb::thread_result_t WorkerPtr(void *pool);
30
31  static void Worker(TaskPoolImpl *pool);
32
33  std::queue<std::function<void()>> m_tasks;
34  std::mutex m_tasks_mutex;
35  uint32_t m_thread_count;
36};
37
38} // end of anonymous namespace
39
40TaskPoolImpl &TaskPoolImpl::GetInstance() {
41  static TaskPoolImpl g_task_pool_impl;
42  return g_task_pool_impl;
43}
44
45void TaskPool::AddTaskImpl(std::function<void()> &&task_fn) {
46  TaskPoolImpl::GetInstance().AddTask(std::move(task_fn));
47}
48
49TaskPoolImpl::TaskPoolImpl() : m_thread_count(0) {}
50
51unsigned GetHardwareConcurrencyHint() {
52  // std::thread::hardware_concurrency may return 0
53  // if the value is not well defined or not computable.
54  static const unsigned g_hardware_concurrency =
55    std::max(1u, std::thread::hardware_concurrency());
56  return g_hardware_concurrency;
57}
58
59void TaskPoolImpl::AddTask(std::function<void()> &&task_fn) {
60  const size_t min_stack_size = 8 * 1024 * 1024;
61
62  std::unique_lock<std::mutex> lock(m_tasks_mutex);
63  m_tasks.emplace(std::move(task_fn));
64  if (m_thread_count < GetHardwareConcurrencyHint()) {
65    m_thread_count++;
66    // Note that this detach call needs to happen with the m_tasks_mutex held.
67    // This prevents the thread
68    // from exiting prematurely and triggering a linux libc bug
69    // (https://sourceware.org/bugzilla/show_bug.cgi?id=19951).
70    lldb_private::ThreadLauncher::LaunchThread("task-pool.worker", WorkerPtr,
71                                               this, nullptr, min_stack_size)
72        .Release();
73  }
74}
75
76lldb::thread_result_t TaskPoolImpl::WorkerPtr(void *pool) {
77  Worker((TaskPoolImpl *)pool);
78  return 0;
79}
80
81void TaskPoolImpl::Worker(TaskPoolImpl *pool) {
82  while (true) {
83    std::unique_lock<std::mutex> lock(pool->m_tasks_mutex);
84    if (pool->m_tasks.empty()) {
85      pool->m_thread_count--;
86      break;
87    }
88
89    std::function<void()> f = std::move(pool->m_tasks.front());
90    pool->m_tasks.pop();
91    lock.unlock();
92
93    f();
94  }
95}
96
97void TaskMapOverInt(size_t begin, size_t end,
98                    const llvm::function_ref<void(size_t)> &func) {
99  const size_t num_workers = std::min<size_t>(end, GetHardwareConcurrencyHint());
100  std::atomic<size_t> idx{begin};
101
102  auto wrapper = [&idx, end, &func]() {
103    while (true) {
104      size_t i = idx.fetch_add(1);
105      if (i >= end)
106        break;
107      func(i);
108    }
109  };
110
111  std::vector<std::future<void>> futures;
112  futures.reserve(num_workers);
113  for (size_t i = 0; i < num_workers; i++)
114    futures.push_back(TaskPool::AddTask(wrapper));
115  for (size_t i = 0; i < num_workers; i++)
116    futures[i].wait();
117}
118
119} // namespace lldb_private
120
121