1 /*
2 *
3 * Copyright 2015 gRPC authors.
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 */
18
19 #include "src/cpp/server/dynamic_thread_pool.h"
20
21 #include <mutex>
22
23 #include <grpc/support/log.h>
24
25 #include "src/core/lib/gprpp/thd.h"
26
27 namespace grpc {
28
DynamicThread(DynamicThreadPool * pool)29 DynamicThreadPool::DynamicThread::DynamicThread(DynamicThreadPool* pool)
30 : pool_(pool),
31 thd_("grpcpp_dynamic_pool",
32 [](void* th) {
33 static_cast<DynamicThreadPool::DynamicThread*>(th)->ThreadFunc();
34 },
35 this) {
36 thd_.Start();
37 }
~DynamicThread()38 DynamicThreadPool::DynamicThread::~DynamicThread() { thd_.Join(); }
39
ThreadFunc()40 void DynamicThreadPool::DynamicThread::ThreadFunc() {
41 pool_->ThreadFunc();
42 // Now that we have killed ourselves, we should reduce the thread count
43 std::unique_lock<std::mutex> lock(pool_->mu_);
44 pool_->nthreads_--;
45 // Move ourselves to dead list
46 pool_->dead_threads_.push_back(this);
47
48 if ((pool_->shutdown_) && (pool_->nthreads_ == 0)) {
49 pool_->shutdown_cv_.notify_one();
50 }
51 }
52
ThreadFunc()53 void DynamicThreadPool::ThreadFunc() {
54 for (;;) {
55 // Wait until work is available or we are shutting down.
56 std::unique_lock<std::mutex> lock(mu_);
57 if (!shutdown_ && callbacks_.empty()) {
58 // If there are too many threads waiting, then quit this thread
59 if (threads_waiting_ >= reserve_threads_) {
60 break;
61 }
62 threads_waiting_++;
63 cv_.wait(lock);
64 threads_waiting_--;
65 }
66 // Drain callbacks before considering shutdown to ensure all work
67 // gets completed.
68 if (!callbacks_.empty()) {
69 auto cb = callbacks_.front();
70 callbacks_.pop();
71 lock.unlock();
72 cb();
73 } else if (shutdown_) {
74 break;
75 }
76 }
77 }
78
DynamicThreadPool(int reserve_threads)79 DynamicThreadPool::DynamicThreadPool(int reserve_threads)
80 : shutdown_(false),
81 reserve_threads_(reserve_threads),
82 nthreads_(0),
83 threads_waiting_(0) {
84 for (int i = 0; i < reserve_threads_; i++) {
85 std::lock_guard<std::mutex> lock(mu_);
86 nthreads_++;
87 new DynamicThread(this);
88 }
89 }
90
ReapThreads(std::list<DynamicThread * > * tlist)91 void DynamicThreadPool::ReapThreads(std::list<DynamicThread*>* tlist) {
92 for (auto t = tlist->begin(); t != tlist->end(); t = tlist->erase(t)) {
93 delete *t;
94 }
95 }
96
~DynamicThreadPool()97 DynamicThreadPool::~DynamicThreadPool() {
98 std::unique_lock<std::mutex> lock(mu_);
99 shutdown_ = true;
100 cv_.notify_all();
101 while (nthreads_ != 0) {
102 shutdown_cv_.wait(lock);
103 }
104 ReapThreads(&dead_threads_);
105 }
106
Add(const std::function<void ()> & callback)107 void DynamicThreadPool::Add(const std::function<void()>& callback) {
108 std::lock_guard<std::mutex> lock(mu_);
109 // Add works to the callbacks list
110 callbacks_.push(callback);
111 // Increase pool size or notify as needed
112 if (threads_waiting_ == 0) {
113 // Kick off a new thread
114 nthreads_++;
115 new DynamicThread(this);
116 } else {
117 cv_.notify_one();
118 }
119 // Also use this chance to harvest dead threads
120 if (!dead_threads_.empty()) {
121 ReapThreads(&dead_threads_);
122 }
123 }
124
125 } // namespace grpc
126