1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
|
#include "util/thread_pool.h"
#include "util/task.h"
#include <glog/logging.h>
#include <condition_variable>
#include <mutex>
#include <queue>
#include <thread>
#include <vector>
using std::chrono::duration;
using std::chrono::duration_cast;
using std::chrono::seconds;
using std::chrono::steady_clock;
using std::condition_variable;
using std::function;
using std::get;
using std::lock_guard;
using std::mutex;
using std::priority_queue;
using std::thread;
using std::tuple;
using std::unique_lock;
using std::vector;
namespace cert_trans {
namespace {
typedef tuple<steady_clock::time_point, function<void()>, util::Task*>
QueueEntry;
struct QueueOrdering {
bool operator()(const QueueEntry& lhs, const QueueEntry& rhs) const {
return get<0>(lhs) > get<0>(rhs);
}
};
} // namespace
class ThreadPool::Impl {
public:
~Impl();
void Worker();
// TODO(pphaneuf): I'd like this to be const, but it required
// jumping through a few more hoops, keeping it simple for now.
vector<thread> threads_;
mutex queue_lock_;
condition_variable queue_cond_var_;
priority_queue<QueueEntry, vector<QueueEntry>, QueueOrdering> queue_;
};
ThreadPool::Impl::~Impl() {
// Start by sending an empty closure to every thread (and notify
// them), to have them exit cleanly.
{
lock_guard<mutex> lock(queue_lock_);
for (int i = threads_.size(); i > 0; --i)
queue_.emplace(
make_tuple(steady_clock::time_point(), function<void()>(), nullptr));
}
// Notify all the threads *after* adding all the empty closures, to
// avoid any races.
queue_cond_var_.notify_all();
// Wait for the threads to exit.
for (auto& thread : threads_) {
thread.join();
}
// Workers should've drained everything from the queue.
CHECK(queue_.empty());
}
void ThreadPool::Impl::Worker() {
while (true) {
QueueEntry entry;
{
unique_lock<mutex> lock(queue_lock_);
while (queue_.empty() || get<0>(queue_.top()) > steady_clock::now()) {
if (queue_.empty()) {
// If there's nothing to do, wait until there is.
queue_cond_var_.wait(lock);
} else {
// Otherwise, wait until the next thing we currently know about is
// ready.
const steady_clock::duration duration(get<0>(queue_.top()) -
steady_clock::now());
queue_cond_var_.wait_for(lock, duration);
}
}
entry = queue_.top();
queue_.pop();
// If we received an empty entry, exit cleanly.
if (!get<1>(entry)) {
// Anything left in the queue must be either other exit sentinels, or
// future (delayed) tasks, so we'll cancel anything we find, up until
// either the next exit sentinel, or the end of the queue.
VLOG(1) << "Cancelling delayed tasks...";
vector<util::Task*> to_be_cancelled;
while (!queue_.empty() && get<2>(queue_.top())) {
to_be_cancelled.push_back(CHECK_NOTNULL(get<2>(queue_.top())));
queue_.pop();
}
// Cancel the callbacks below outside of the lock to avoid deadlocking
// anyone who tries to Add() more stuff when they're cancelled.
// Anyone who does that is going to cause a CHECK fail in the d'tor of
// the pool anyway, but at least they'll know about it that way.
lock.unlock();
for (const auto& t : to_be_cancelled) {
t->Return(util::Status::CANCELLED);
}
VLOG(1) << "Cancelled " << to_be_cancelled.size() << " delayed tasks.";
return;
}
}
// Make sure not to hold the lock while calling the closure.
get<1>(entry)();
}
}
ThreadPool::ThreadPool()
: ThreadPool(thread::hardware_concurrency() > 0
? thread::hardware_concurrency()
: 1) {
}
ThreadPool::ThreadPool(size_t num_threads) : impl_(new Impl) {
CHECK_GT(num_threads, static_cast<size_t>(0));
LOG(INFO) << "ThreadPool starting with " << num_threads << " threads";
for (int i = 0; i < static_cast<int64_t>(num_threads); ++i)
impl_->threads_.emplace_back(thread(&Impl::Worker, impl_.get()));
}
ThreadPool::~ThreadPool() {
// Need to have this method defined where the definition of
// ThreadPool::Impl is visible.
}
void ThreadPool::Add(const function<void()>& closure) {
// Empty closures signal a thread to exit, don't allow that (also,
// it doesn't make sense).
if (!closure) {
return;
}
{
lock_guard<mutex> lock(impl_->queue_lock_);
impl_->queue_.emplace(make_tuple(steady_clock::now(), closure, nullptr));
}
impl_->queue_cond_var_.notify_one();
}
void ThreadPool::Delay(const duration<double>& delay, util::Task* task) {
CHECK_NOTNULL(task);
{
lock_guard<mutex> lock(impl_->queue_lock_);
impl_->queue_.emplace(make_tuple(
steady_clock::now() + duration_cast<std::chrono::microseconds>(delay),
[task]() { task->Return(); }, task));
}
impl_->queue_cond_var_.notify_one();
}
} // namespace cert_trans
|
