1/* Copyright 2019 The TensorFlow Authors. All Rights Reserved.
2
3Licensed under the Apache License, Version 2.0 (the "License");
4you may not use this file except in compliance with the License.
5You may obtain a copy of the License at
6
7 http://www.apache.org/licenses/LICENSE-2.0
8
9Unless required by applicable law or agreed to in writing, software
10distributed under the License is distributed on an "AS IS" BASIS,
11WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12See the License for the specific language governing permissions and
13limitations under the License.
14==============================================================================*/
15
16#include "tensorflow/core/data/unbounded_thread_pool.h"
17
18#include "absl/memory/memory.h"
19#include "tensorflow/core/framework/dataset.h"
20#include "tensorflow/core/lib/core/notification.h"
21#include "tensorflow/core/platform/env.h"
22#include "tensorflow/core/platform/resource.h"
23#include "tensorflow/core/platform/unbounded_work_queue.h"
24
25namespace tensorflow {
26namespace data {
27
28// A logical implementation of the `tensorflow::Thread` interface that uses
29// physical threads in an `UnboundedThreadPool` to perform the work.
30//
31// NOTE: This object represents a logical thread of control that may be mapped
32// onto the same physical thread as other work items that are submitted to the
33// same `UnboundedThreadPool`.
34class UnboundedThreadPool::LogicalThreadWrapper : public Thread {
35 public:
36 explicit LogicalThreadWrapper(std::shared_ptr<Notification> done)
37 : done_(std::move(done)) {}
38
39 ~LogicalThreadWrapper() override {
40 // NOTE: The `Thread` destructor is expected to "join" the created thread,
41 // but the physical thread may continue to execute after the work for this
42 // thread is complete. We simulate this by waiting on a notification that
43 // the thread's work function will notify when it is complete.
44 done_->WaitForNotification();
45 }
46
47 private:
48 std::shared_ptr<Notification> done_;
49};
50
51// A lightweight wrapper for creating logical threads in a `UnboundedThreadPool`
52// that can be shared (e.g.) in an `IteratorContext`.
53class UnboundedThreadPool::LogicalThreadFactory : public ThreadFactory {
54 public:
55 explicit LogicalThreadFactory(UnboundedThreadPool* pool) : pool_(pool) {}
56
57 std::unique_ptr<Thread> StartThread(const string& name,
58 std::function<void()> fn) override {
59 auto done = std::make_shared<Notification>();
60 pool_->ScheduleOnWorkQueue(std::move(fn), done);
61 return std::make_unique<LogicalThreadWrapper>(std::move(done));
62 }
63
64 private:
65 UnboundedThreadPool* const pool_; // Not owned.
66};
67
68std::shared_ptr<ThreadFactory> UnboundedThreadPool::get_thread_factory() {
69 return std::make_shared<LogicalThreadFactory>(this);
70}
71
72void UnboundedThreadPool::Schedule(std::function<void()> fn) {
73 auto tagged_fn = [fn = std::move(fn)]() {
74 tensorflow::ResourceTagger tag(kTFDataResourceTag, "ThreadPool");
75 fn();
76 };
77 ScheduleOnWorkQueue(std::move(tagged_fn), /*done=*/nullptr);
78}
79
80int UnboundedThreadPool::NumThreads() const { return -1; }
81
82int UnboundedThreadPool::CurrentThreadId() const { return -1; }
83
84namespace {
85void WorkQueueFunc(const std::function<void()>& fn,
86 std::shared_ptr<Notification> done) {
87 fn();
88 if (done) {
89 done->Notify();
90 }
91}
92} // namespace
93
94void UnboundedThreadPool::ScheduleOnWorkQueue(
95 std::function<void()> fn, std::shared_ptr<Notification> done) {
96 unbounded_work_queue_.Schedule(
97 std::bind(&WorkQueueFunc, std::move(fn), std::move(done)));
98}
99
100} // namespace data
101} // namespace tensorflow
102