1 //
2 // Copyright 2016 The Android Open Source Project
3 //
4 // Licensed under the Apache License, Version 2.0 (the "License");
5 // you may not use this file except in compliance with the License.
6 // You may obtain a copy of the License at
7 //
8 // http://www.apache.org/licenses/LICENSE-2.0
9 //
10 // Unless required by applicable law or agreed to in writing, software
11 // distributed under the License is distributed on an "AS IS" BASIS,
12 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 // See the License for the specific language governing permissions and
14 // limitations under the License.
15 //
16 
17 #include "async_fd_watcher.h"
18 
19 #include <algorithm>
20 #include <atomic>
21 #include <condition_variable>
22 #include <map>
23 #include <mutex>
24 #include <thread>
25 #include <vector>
26 #include "fcntl.h"
27 #include "sys/select.h"
28 #include "unistd.h"
29 
30 static const int INVALID_FD = -1;
31 
32 namespace android {
33 namespace hardware {
34 namespace bluetooth {
35 namespace async {
36 
37 int AsyncFdWatcher::WatchFdForNonBlockingReads(
38     int file_descriptor, const ReadCallback& on_read_fd_ready_callback) {
39   // Add file descriptor and callback
40   {
41     std::unique_lock<std::mutex> guard(internal_mutex_);
42     watched_fds_[file_descriptor] = on_read_fd_ready_callback;
43   }
44 
45   // Start the thread if not started yet
46   return tryStartThread();
47 }
48 
49 int AsyncFdWatcher::ConfigureTimeout(
50     const std::chrono::milliseconds timeout,
51     const TimeoutCallback& on_timeout_callback) {
52   // Add timeout and callback
53   {
54     std::unique_lock<std::mutex> guard(timeout_mutex_);
55     timeout_cb_ = on_timeout_callback;
56     timeout_ms_ = timeout;
57   }
58 
59   notifyThread();
60   return 0;
61 }
62 
63 void AsyncFdWatcher::StopWatchingFileDescriptors() { stopThread(); }
64 
65 AsyncFdWatcher::~AsyncFdWatcher() {}
66 
67 // Make sure to call this with at least one file descriptor ready to be
68 // watched upon or the thread routine will return immediately
69 int AsyncFdWatcher::tryStartThread() {
70   if (std::atomic_exchange(&running_, true)) return 0;
71 
72   // Set up the communication channel
73   int pipe_fds[2];
74   if (pipe2(pipe_fds, O_NONBLOCK)) return -1;
75 
76   notification_listen_fd_ = pipe_fds[0];
77   notification_write_fd_ = pipe_fds[1];
78 
79   thread_ = std::thread([this]() { ThreadRoutine(); });
80   if (!thread_.joinable()) return -1;
81 
82   return 0;
83 }
84 
85 int AsyncFdWatcher::stopThread() {
86   if (!std::atomic_exchange(&running_, false)) return 0;
87 
88   notifyThread();
89   if (std::this_thread::get_id() != thread_.get_id()) {
90     thread_.join();
91   }
92 
93   {
94     std::unique_lock<std::mutex> guard(internal_mutex_);
95     watched_fds_.clear();
96   }
97 
98   {
99     std::unique_lock<std::mutex> guard(timeout_mutex_);
100     timeout_cb_ = nullptr;
101   }
102 
103   return 0;
104 }
105 
106 int AsyncFdWatcher::notifyThread() {
107   uint8_t buffer[] = {0};
108   if (TEMP_FAILURE_RETRY(write(notification_write_fd_, &buffer, 1)) < 0) {
109     return -1;
110   }
111   return 0;
112 }
113 
114 void AsyncFdWatcher::ThreadRoutine() {
115   while (running_) {
116     fd_set read_fds;
117     FD_ZERO(&read_fds);
118     FD_SET(notification_listen_fd_, &read_fds);
119     int max_read_fd = INVALID_FD;
120     for (auto& it : watched_fds_) {
121       FD_SET(it.first, &read_fds);
122       max_read_fd = std::max(max_read_fd, it.first);
123     }
124 
125     struct timeval timeout;
126     struct timeval* timeout_ptr = NULL;
127     if (timeout_ms_ > std::chrono::milliseconds(0)) {
128       timeout.tv_sec = timeout_ms_.count() / 1000;
129       timeout.tv_usec = (timeout_ms_.count() % 1000) * 1000;
130       timeout_ptr = &timeout;
131     }
132 
133     // Wait until there is data available to read on some FD.
134     int nfds = std::max(notification_listen_fd_, max_read_fd);
135     int retval = select(nfds + 1, &read_fds, NULL, NULL, timeout_ptr);
136 
137     // There was some error.
138     if (retval < 0) continue;
139 
140     // Timeout.
141     if (retval == 0) {
142       // Allow the timeout callback to modify the timeout.
143       TimeoutCallback saved_cb;
144       {
145         std::unique_lock<std::mutex> guard(timeout_mutex_);
146         if (timeout_ms_ > std::chrono::milliseconds(0)) saved_cb = timeout_cb_;
147       }
148       if (saved_cb != nullptr) saved_cb();
149       continue;
150     }
151 
152     // Read data from the notification FD.
153     if (FD_ISSET(notification_listen_fd_, &read_fds)) {
154       char buffer[] = {0};
155       TEMP_FAILURE_RETRY(read(notification_listen_fd_, buffer, 1));
156       continue;
157     }
158 
159     // Invoke the data ready callbacks if appropriate.
160     std::vector<decltype(watched_fds_)::value_type> saved_callbacks;
161     {
162       std::unique_lock<std::mutex> guard(internal_mutex_);
163       for (auto& it : watched_fds_) {
164         if (FD_ISSET(it.first, &read_fds)) {
165           saved_callbacks.push_back(it);
166         }
167       }
168     }
169 
170     for (auto& it : saved_callbacks) {
171       if (it.second) {
172         it.second(it.first);
173       }
174     }
175   }
176 }
177 
178 }  // namespace async
179 }  // namespace bluetooth
180 }  // namespace hardware
181 }  // namespace android
182