121 lines
3.2 KiB
C++
121 lines
3.2 KiB
C++
//===--------------------- TaskPool.cpp -------------------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "lldb/Host/TaskPool.h"
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#include "lldb/Host/ThreadLauncher.h"
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#include <cstdint> // for uint32_t
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#include <queue> // for queue
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#include <thread> // for thread
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namespace lldb_private {
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namespace {
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class TaskPoolImpl {
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public:
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static TaskPoolImpl &GetInstance();
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void AddTask(std::function<void()> &&task_fn);
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private:
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TaskPoolImpl();
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static lldb::thread_result_t WorkerPtr(void *pool);
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static void Worker(TaskPoolImpl *pool);
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std::queue<std::function<void()>> m_tasks;
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std::mutex m_tasks_mutex;
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uint32_t m_thread_count;
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};
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} // end of anonymous namespace
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TaskPoolImpl &TaskPoolImpl::GetInstance() {
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static TaskPoolImpl g_task_pool_impl;
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return g_task_pool_impl;
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}
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void TaskPool::AddTaskImpl(std::function<void()> &&task_fn) {
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TaskPoolImpl::GetInstance().AddTask(std::move(task_fn));
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}
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TaskPoolImpl::TaskPoolImpl() : m_thread_count(0) {}
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unsigned GetHardwareConcurrencyHint() {
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// std::thread::hardware_concurrency may return 0
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// if the value is not well defined or not computable.
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static const unsigned g_hardware_concurrency =
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std::max(1u, std::thread::hardware_concurrency());
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return g_hardware_concurrency;
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}
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void TaskPoolImpl::AddTask(std::function<void()> &&task_fn) {
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const size_t min_stack_size = 8 * 1024 * 1024;
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std::unique_lock<std::mutex> lock(m_tasks_mutex);
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m_tasks.emplace(std::move(task_fn));
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if (m_thread_count < GetHardwareConcurrencyHint()) {
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m_thread_count++;
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// Note that this detach call needs to happen with the m_tasks_mutex held.
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// This prevents the thread
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// from exiting prematurely and triggering a linux libc bug
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// (https://sourceware.org/bugzilla/show_bug.cgi?id=19951).
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lldb_private::ThreadLauncher::LaunchThread("task-pool.worker", WorkerPtr,
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this, nullptr, min_stack_size)
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.Release();
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}
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}
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lldb::thread_result_t TaskPoolImpl::WorkerPtr(void *pool) {
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Worker((TaskPoolImpl *)pool);
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return 0;
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}
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void TaskPoolImpl::Worker(TaskPoolImpl *pool) {
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while (true) {
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std::unique_lock<std::mutex> lock(pool->m_tasks_mutex);
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if (pool->m_tasks.empty()) {
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pool->m_thread_count--;
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break;
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}
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std::function<void()> f = std::move(pool->m_tasks.front());
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pool->m_tasks.pop();
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lock.unlock();
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f();
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}
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}
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void TaskMapOverInt(size_t begin, size_t end,
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const llvm::function_ref<void(size_t)> &func) {
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const size_t num_workers = std::min<size_t>(end, GetHardwareConcurrencyHint());
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std::atomic<size_t> idx{begin};
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auto wrapper = [&idx, end, &func]() {
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while (true) {
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size_t i = idx.fetch_add(1);
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if (i >= end)
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break;
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func(i);
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}
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};
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std::vector<std::future<void>> futures;
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futures.reserve(num_workers);
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for (size_t i = 0; i < num_workers; i++)
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futures.push_back(TaskPool::AddTask(wrapper));
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for (size_t i = 0; i < num_workers; i++)
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futures[i].wait();
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}
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} // namespace lldb_private
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