1 //===--------------------- TaskPool.cpp -------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #include "lldb/Host/TaskPool.h"
10 #include "lldb/Host/ThreadLauncher.h"
11 #include "lldb/Utility/Log.h"
12
13 #include <cstdint>
14 #include <queue>
15 #include <thread>
16
17 namespace lldb_private {
18
19 namespace {
20 class TaskPoolImpl {
21 public:
22 static TaskPoolImpl &GetInstance();
23
24 void AddTask(std::function<void()> &&task_fn);
25
26 private:
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
GetInstance()40 TaskPoolImpl &TaskPoolImpl::GetInstance() {
41 static TaskPoolImpl g_task_pool_impl;
42 return g_task_pool_impl;
43 }
44
AddTaskImpl(std::function<void ()> && task_fn)45 void TaskPool::AddTaskImpl(std::function<void()> &&task_fn) {
46 TaskPoolImpl::GetInstance().AddTask(std::move(task_fn));
47 }
48
TaskPoolImpl()49 TaskPoolImpl::TaskPoolImpl() : m_thread_count(0) {}
50
GetHardwareConcurrencyHint()51 unsigned GetHardwareConcurrencyHint() {
52 // std::thread::hardware_concurrency may return 0 if the value is not well
53 // 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
AddTask(std::function<void ()> && task_fn)59 void 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 from exiting prematurely and triggering a linux
68 // libc bug (https://sourceware.org/bugzilla/show_bug.cgi?id=19951).
69 llvm::Expected<HostThread> host_thread =
70 lldb_private::ThreadLauncher::LaunchThread(
71 "task-pool.worker", WorkerPtr, this, min_stack_size);
72 if (host_thread) {
73 host_thread->Release();
74 } else {
75 LLDB_LOG(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_HOST),
76 "failed to launch host thread: {}",
77 llvm::toString(host_thread.takeError()));
78 }
79 }
80 }
81
WorkerPtr(void * pool)82 lldb::thread_result_t TaskPoolImpl::WorkerPtr(void *pool) {
83 Worker((TaskPoolImpl *)pool);
84 return {};
85 }
86
Worker(TaskPoolImpl * pool)87 void TaskPoolImpl::Worker(TaskPoolImpl *pool) {
88 while (true) {
89 std::unique_lock<std::mutex> lock(pool->m_tasks_mutex);
90 if (pool->m_tasks.empty()) {
91 pool->m_thread_count--;
92 break;
93 }
94
95 std::function<void()> f = std::move(pool->m_tasks.front());
96 pool->m_tasks.pop();
97 lock.unlock();
98
99 f();
100 }
101 }
102
TaskMapOverInt(size_t begin,size_t end,const llvm::function_ref<void (size_t)> & func)103 void TaskMapOverInt(size_t begin, size_t end,
104 const llvm::function_ref<void(size_t)> &func) {
105 const size_t num_workers = std::min<size_t>(end, GetHardwareConcurrencyHint());
106 std::atomic<size_t> idx{begin};
107
108 auto wrapper = [&idx, end, &func]() {
109 while (true) {
110 size_t i = idx.fetch_add(1);
111 if (i >= end)
112 break;
113 func(i);
114 }
115 };
116
117 std::vector<std::future<void>> futures;
118 futures.reserve(num_workers);
119 for (size_t i = 0; i < num_workers; i++)
120 futures.push_back(TaskPool::AddTask(wrapper));
121 for (size_t i = 0; i < num_workers; i++)
122 futures[i].wait();
123 }
124
125 } // namespace lldb_private
126
127