From ef5d0b5e97ec8e6fa395d377b09aa7755e345b4f Mon Sep 17 00:00:00 2001
From: Dimitry Andric <dim@FreeBSD.org>
Date: Mon, 18 Dec 2017 20:12:36 +0000
Subject: Vendor import of lldb trunk r321017:
 https://llvm.org/svn/llvm-project/lldb/trunk@321017

---
 source/Host/common/TaskPool.cpp | 120 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 source/Host/common/TaskPool.cpp

(limited to 'source/Host/common/TaskPool.cpp')

diff --git a/source/Host/common/TaskPool.cpp b/source/Host/common/TaskPool.cpp
new file mode 100644
index 000000000000..156a07942998
--- /dev/null
+++ b/source/Host/common/TaskPool.cpp
@@ -0,0 +1,120 @@
+//===--------------------- TaskPool.cpp -------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/Host/TaskPool.h"
+#include "lldb/Host/ThreadLauncher.h"
+
+#include <cstdint> // for uint32_t
+#include <queue>   // for queue
+#include <thread>  // for thread
+
+namespace lldb_private {
+
+namespace {
+class TaskPoolImpl {
+public:
+  static TaskPoolImpl &GetInstance();
+
+  void AddTask(std::function<void()> &&task_fn);
+
+private:
+  TaskPoolImpl();
+
+  static lldb::thread_result_t WorkerPtr(void *pool);
+
+  static void Worker(TaskPoolImpl *pool);
+
+  std::queue<std::function<void()>> m_tasks;
+  std::mutex m_tasks_mutex;
+  uint32_t m_thread_count;
+};
+
+} // end of anonymous namespace
+
+TaskPoolImpl &TaskPoolImpl::GetInstance() {
+  static TaskPoolImpl g_task_pool_impl;
+  return g_task_pool_impl;
+}
+
+void TaskPool::AddTaskImpl(std::function<void()> &&task_fn) {
+  TaskPoolImpl::GetInstance().AddTask(std::move(task_fn));
+}
+
+TaskPoolImpl::TaskPoolImpl() : m_thread_count(0) {}
+
+unsigned GetHardwareConcurrencyHint() {
+  // std::thread::hardware_concurrency may return 0
+  // if the value is not well defined or not computable.
+  static const unsigned g_hardware_concurrency = 
+    std::max(1u, std::thread::hardware_concurrency());
+  return g_hardware_concurrency;
+}
+
+void TaskPoolImpl::AddTask(std::function<void()> &&task_fn) {
+  const size_t min_stack_size = 8 * 1024 * 1024;
+
+  std::unique_lock<std::mutex> lock(m_tasks_mutex);
+  m_tasks.emplace(std::move(task_fn));
+  if (m_thread_count < GetHardwareConcurrencyHint()) {
+    m_thread_count++;
+    // Note that this detach call needs to happen with the m_tasks_mutex held.
+    // This prevents the thread
+    // from exiting prematurely and triggering a linux libc bug
+    // (https://sourceware.org/bugzilla/show_bug.cgi?id=19951).
+    lldb_private::ThreadLauncher::LaunchThread("task-pool.worker", WorkerPtr,
+                                               this, nullptr, min_stack_size)
+        .Release();
+  }
+}
+
+lldb::thread_result_t TaskPoolImpl::WorkerPtr(void *pool) {
+  Worker((TaskPoolImpl *)pool);
+  return 0;
+}
+
+void TaskPoolImpl::Worker(TaskPoolImpl *pool) {
+  while (true) {
+    std::unique_lock<std::mutex> lock(pool->m_tasks_mutex);
+    if (pool->m_tasks.empty()) {
+      pool->m_thread_count--;
+      break;
+    }
+
+    std::function<void()> f = std::move(pool->m_tasks.front());
+    pool->m_tasks.pop();
+    lock.unlock();
+
+    f();
+  }
+}
+
+void TaskMapOverInt(size_t begin, size_t end,
+                    const llvm::function_ref<void(size_t)> &func) {
+  const size_t num_workers = std::min<size_t>(end, GetHardwareConcurrencyHint());
+  std::atomic<size_t> idx{begin};
+  
+  auto wrapper = [&idx, end, &func]() {
+    while (true) {
+      size_t i = idx.fetch_add(1);
+      if (i >= end)
+        break;
+      func(i);
+    }
+  };
+
+  std::vector<std::future<void>> futures;
+  futures.reserve(num_workers);
+  for (size_t i = 0; i < num_workers; i++)
+    futures.push_back(TaskPool::AddTask(wrapper));
+  for (size_t i = 0; i < num_workers; i++)
+    futures[i].wait();
+}
+
+} // namespace lldb_private
+
-- 
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