2 * Copyright 2014 Facebook, Inc.
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
17 #ifndef __STDC_FORMAT_MACROS
18 #define __STDC_FORMAT_MACROS
21 #include <folly/io/async/AsyncServerSocket.h>
23 #include <folly/io/async/EventBase.h>
24 #include <folly/io/async/NotificationQueue.h>
25 #include <folly/SocketAddress.h>
31 #include <sys/types.h>
32 #include <sys/socket.h>
33 #include <netinet/tcp.h>
37 const uint32_t AsyncServerSocket::kDefaultMaxAcceptAtOnce;
38 const uint32_t AsyncServerSocket::kDefaultCallbackAcceptAtOnce;
39 const uint32_t AsyncServerSocket::kDefaultMaxMessagesInQueue;
41 int setCloseOnExec(int fd, int value) {
42 // Read the current flags
43 int old_flags = fcntl(fd, F_GETFD, 0);
45 // If reading the flags failed, return error indication now
49 // Set just the flag we want to set
52 new_flags = old_flags | FD_CLOEXEC;
54 new_flags = old_flags & ~FD_CLOEXEC;
56 // Store modified flag word in the descriptor
57 return fcntl(fd, F_SETFD, new_flags);
60 void AsyncServerSocket::RemoteAcceptor::start(
61 EventBase* eventBase, uint32_t maxAtOnce, uint32_t maxInQueue) {
62 setMaxReadAtOnce(maxAtOnce);
63 queue_.setMaxQueueSize(maxInQueue);
65 if (!eventBase->runInEventBaseThread([=](){
66 callback_->acceptStarted();
67 this->startConsuming(eventBase, &queue_);
69 throw std::invalid_argument("unable to start waiting on accept "
70 "notification queue in the specified "
75 void AsyncServerSocket::RemoteAcceptor::stop(
76 EventBase* eventBase, AcceptCallback* callback) {
77 if (!eventBase->runInEventBaseThread([=](){
78 callback->acceptStopped();
81 throw std::invalid_argument("unable to start waiting on accept "
82 "notification queue in the specified "
87 void AsyncServerSocket::RemoteAcceptor::messageAvailable(
91 case MessageType::MSG_NEW_CONN:
93 callback_->connectionAccepted(msg.fd, msg.address);
96 case MessageType::MSG_ERROR:
98 std::runtime_error ex(msg.msg);
99 callback_->acceptError(ex);
104 LOG(ERROR) << "invalid accept notification message type "
106 std::runtime_error ex(
107 "received invalid accept notification message type");
108 callback_->acceptError(ex);
114 * AsyncServerSocket::BackoffTimeout
116 class AsyncServerSocket::BackoffTimeout : public AsyncTimeout {
118 BackoffTimeout(AsyncServerSocket* socket)
119 : AsyncTimeout(socket->getEventBase()),
122 virtual void timeoutExpired() noexcept {
123 socket_->backoffTimeoutExpired();
127 AsyncServerSocket* socket_;
131 * AsyncServerSocket methods
134 AsyncServerSocket::AsyncServerSocket(EventBase* eventBase)
135 : eventBase_(eventBase),
137 maxAcceptAtOnce_(kDefaultMaxAcceptAtOnce),
138 maxNumMsgsInQueue_(kDefaultMaxMessagesInQueue),
139 acceptRateAdjustSpeed_(0),
141 lastAccepTimestamp_(std::chrono::steady_clock::now()),
142 numDroppedConnections_(0),
144 backoffTimeout_(nullptr),
146 keepAliveEnabled_(true),
148 shutdownSocketSet_(nullptr) {
151 void AsyncServerSocket::setShutdownSocketSet(ShutdownSocketSet* newSS) {
152 if (shutdownSocketSet_ == newSS) {
155 if (shutdownSocketSet_) {
156 for (auto& h : sockets_) {
157 shutdownSocketSet_->remove(h.socket_);
160 shutdownSocketSet_ = newSS;
161 if (shutdownSocketSet_) {
162 for (auto& h : sockets_) {
163 shutdownSocketSet_->add(h.socket_);
168 AsyncServerSocket::~AsyncServerSocket() {
169 assert(callbacks_.empty());
172 int AsyncServerSocket::stopAccepting(int shutdownFlags) {
174 for (auto& handler : sockets_) {
175 VLOG(10) << "AsyncServerSocket::stopAccepting " << this <<
178 assert(eventBase_ == nullptr || eventBase_->isInEventBaseThread());
180 // When destroy is called, unregister and close the socket immediately
183 for (auto& handler : sockets_) {
184 handler.unregisterHandler();
185 if (shutdownSocketSet_) {
186 shutdownSocketSet_->close(handler.socket_);
187 } else if (shutdownFlags >= 0) {
188 result = ::shutdown(handler.socket_, shutdownFlags);
189 pendingCloseSockets_.push_back(handler.socket_);
191 ::close(handler.socket_);
196 // Destroy the backoff timout. This will cancel it if it is running.
197 delete backoffTimeout_;
198 backoffTimeout_ = nullptr;
200 // Close all of the callback queues to notify them that they are being
201 // destroyed. No one should access the AsyncServerSocket any more once
202 // destroy() is called. However, clear out callbacks_ before invoking the
203 // accept callbacks just in case. This will potentially help us detect the
204 // bug if one of the callbacks calls addAcceptCallback() or
205 // removeAcceptCallback().
206 std::vector<CallbackInfo> callbacksCopy;
207 callbacks_.swap(callbacksCopy);
208 for (std::vector<CallbackInfo>::iterator it = callbacksCopy.begin();
209 it != callbacksCopy.end();
211 it->consumer->stop(it->eventBase, it->callback);
217 void AsyncServerSocket::destroy() {
219 for (auto s: pendingCloseSockets_) {
222 // Then call DelayedDestruction::destroy() to take care of
223 // whether or not we need immediate or delayed destruction
224 DelayedDestruction::destroy();
227 void AsyncServerSocket::attachEventBase(EventBase *eventBase) {
228 assert(eventBase_ == nullptr);
229 assert(eventBase->isInEventBaseThread());
231 eventBase_ = eventBase;
232 for (auto& handler : sockets_) {
233 handler.attachEventBase(eventBase);
237 void AsyncServerSocket::detachEventBase() {
238 assert(eventBase_ != nullptr);
239 assert(eventBase_->isInEventBaseThread());
242 eventBase_ = nullptr;
243 for (auto& handler : sockets_) {
244 handler.detachEventBase();
248 void AsyncServerSocket::useExistingSockets(const std::vector<int>& fds) {
249 assert(eventBase_ == nullptr || eventBase_->isInEventBaseThread());
251 if (sockets_.size() > 0) {
252 throw std::invalid_argument(
253 "cannot call useExistingSocket() on a "
254 "AsyncServerSocket that already has a socket");
258 // Set addressFamily_ from this socket.
259 // Note that the socket may not have been bound yet, but
260 // setFromLocalAddress() will still work and get the correct address family.
261 // We will update addressFamily_ again anyway if bind() is called later.
262 SocketAddress address;
263 address.setFromLocalAddress(fd);
267 ServerEventHandler(eventBase_, fd, this, address.getFamily()));
268 sockets_.back().changeHandlerFD(fd);
272 void AsyncServerSocket::useExistingSocket(int fd) {
273 useExistingSockets({fd});
276 void AsyncServerSocket::bindSocket(
278 const SocketAddress& address,
279 bool isExistingSocket) {
280 sockaddr_storage addrStorage;
281 address.getAddress(&addrStorage);
282 sockaddr* saddr = reinterpret_cast<sockaddr*>(&addrStorage);
283 if (::bind(fd, saddr, address.getActualSize()) != 0) {
284 if (!isExistingSocket) {
287 folly::throwSystemError(errno,
288 "failed to bind to async server socket: " +
292 // If we just created this socket, update the EventHandler and set socket_
293 if (!isExistingSocket) {
295 ServerEventHandler(eventBase_, fd, this, address.getFamily()));
299 void AsyncServerSocket::bind(const SocketAddress& address) {
300 assert(eventBase_ == nullptr || eventBase_->isInEventBaseThread());
302 // useExistingSocket() may have been called to initialize socket_ already.
303 // However, in the normal case we need to create a new socket now.
304 // Don't set socket_ yet, so that socket_ will remain uninitialized if an
307 if (sockets_.size() == 0) {
308 fd = createSocket(address.getFamily());
309 } else if (sockets_.size() == 1) {
310 if (address.getFamily() != sockets_[0].addressFamily_) {
311 throw std::invalid_argument(
312 "Attempted to bind address to socket with "
313 "different address family");
315 fd = sockets_[0].socket_;
317 throw std::invalid_argument(
318 "Attempted to bind to multiple fds");
321 bindSocket(fd, address, !sockets_.empty());
324 void AsyncServerSocket::bind(
325 const std::vector<IPAddress>& ipAddresses,
327 if (ipAddresses.empty()) {
328 throw std::invalid_argument("No ip addresses were provided");
330 if (!sockets_.empty()) {
331 throw std::invalid_argument("Cannot call bind on a AsyncServerSocket "
332 "that already has a socket.");
335 for (const IPAddress& ipAddress : ipAddresses) {
336 SocketAddress address(ipAddress.toFullyQualified(), port);
337 int fd = createSocket(address.getFamily());
339 bindSocket(fd, address, false);
341 if (sockets_.size() == 0) {
342 throw std::runtime_error(
343 "did not bind any async server socket for port and addresses");
347 void AsyncServerSocket::bind(uint16_t port) {
348 struct addrinfo hints, *res, *res0;
349 char sport[sizeof("65536")];
351 memset(&hints, 0, sizeof(hints));
352 hints.ai_family = AF_UNSPEC;
353 hints.ai_socktype = SOCK_STREAM;
354 hints.ai_flags = AI_PASSIVE;
355 snprintf(sport, sizeof(sport), "%u", port);
357 if (getaddrinfo(nullptr, sport, &hints, &res0)) {
358 throw std::invalid_argument(
359 "Attempted to bind address to socket with "
363 folly::ScopeGuard guard = folly::makeGuard([&]{
368 for (res = res0; res; res = res->ai_next) {
369 int s = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
370 // IPv6/IPv4 may not be supported by the kernel
371 if (s < 0 && errno == EAFNOSUPPORT) {
383 if (res->ai_family == AF_INET6) {
385 CHECK(0 == setsockopt(s, IPPROTO_IPV6, IPV6_V6ONLY,
386 &v6only, sizeof(v6only)));
389 SocketAddress address;
390 address.setFromLocalAddress(s);
393 ServerEventHandler(eventBase_, s, this, address.getFamily()));
395 // Bind to the socket
396 if (::bind(s, res->ai_addr, res->ai_addrlen) != 0) {
397 folly::throwSystemError(
399 "failed to bind to async server socket for port");
402 if (sockets_.size() == 0) {
403 throw std::runtime_error(
404 "did not bind any async server socket for port");
408 void AsyncServerSocket::listen(int backlog) {
409 assert(eventBase_ == nullptr || eventBase_->isInEventBaseThread());
412 for (auto& handler : sockets_) {
413 if (::listen(handler.socket_, backlog) == -1) {
414 folly::throwSystemError(errno,
415 "failed to listen on async server socket");
420 void AsyncServerSocket::getAddress(SocketAddress* addressReturn) const {
421 CHECK(sockets_.size() >= 1);
422 if (sockets_.size() > 1) {
423 VLOG(2) << "Warning: getAddress can return multiple addresses, " <<
424 "but getAddress was called, so only returning the first";
426 addressReturn->setFromLocalAddress(sockets_[0].socket_);
429 std::vector<SocketAddress> AsyncServerSocket::getAddresses()
431 CHECK(sockets_.size() >= 1);
432 auto tsaVec = std::vector<SocketAddress>(sockets_.size());
433 auto tsaIter = tsaVec.begin();
434 for (const auto& socket : sockets_) {
435 (tsaIter++)->setFromLocalAddress(socket.socket_);
440 void AsyncServerSocket::addAcceptCallback(AcceptCallback *callback,
441 EventBase *eventBase,
442 uint32_t maxAtOnce) {
443 assert(eventBase_ == nullptr || eventBase_->isInEventBaseThread());
445 // If this is the first accept callback and we are supposed to be accepting,
446 // start accepting once the callback is installed.
447 bool runStartAccepting = accepting_ && callbacks_.empty();
450 eventBase = eventBase_; // Run in AsyncServerSocket's eventbase
453 callbacks_.push_back(CallbackInfo(callback, eventBase));
455 // Start the remote acceptor.
457 // It would be nice if we could avoid starting the remote acceptor if
458 // eventBase == eventBase_. However, that would cause issues if
459 // detachEventBase() and attachEventBase() were ever used to change the
460 // primary EventBase for the server socket. Therefore we require the caller
461 // to specify a nullptr EventBase if they want to ensure that the callback is
462 // always invoked in the primary EventBase, and to be able to invoke that
463 // callback more efficiently without having to use a notification queue.
464 RemoteAcceptor* acceptor = nullptr;
466 acceptor = new RemoteAcceptor(callback);
467 acceptor->start(eventBase, maxAtOnce, maxNumMsgsInQueue_);
469 callbacks_.pop_back();
473 callbacks_.back().consumer = acceptor;
475 // If this is the first accept callback and we are supposed to be accepting,
477 if (runStartAccepting) {
482 void AsyncServerSocket::removeAcceptCallback(AcceptCallback *callback,
483 EventBase *eventBase) {
484 assert(eventBase_ == nullptr || eventBase_->isInEventBaseThread());
486 // Find the matching AcceptCallback.
487 // We just do a simple linear search; we don't expect removeAcceptCallback()
488 // to be called frequently, and we expect there to only be a small number of
490 std::vector<CallbackInfo>::iterator it = callbacks_.begin();
493 if (it == callbacks_.end()) {
494 throw std::runtime_error("AsyncServerSocket::removeAcceptCallback(): "
495 "accept callback not found");
497 if (it->callback == callback &&
498 (it->eventBase == eventBase || eventBase == nullptr)) {
505 // Remove this callback from callbacks_.
507 // Do this before invoking the acceptStopped() callback, in case
508 // acceptStopped() invokes one of our methods that examines callbacks_.
510 // Save a copy of the CallbackInfo first.
511 CallbackInfo info(*it);
512 callbacks_.erase(it);
513 if (n < callbackIndex_) {
514 // We removed an element before callbackIndex_. Move callbackIndex_ back
515 // one step, since things after n have been shifted back by 1.
518 // We removed something at or after callbackIndex_.
519 // If we removed the last element and callbackIndex_ was pointing at it,
520 // we need to reset callbackIndex_ to 0.
521 if (callbackIndex_ >= callbacks_.size()) {
526 info.consumer->stop(info.eventBase, info.callback);
528 // If we are supposed to be accepting but the last accept callback
529 // was removed, unregister for events until a callback is added.
530 if (accepting_ && callbacks_.empty()) {
531 for (auto& handler : sockets_) {
532 handler.unregisterHandler();
537 void AsyncServerSocket::startAccepting() {
538 assert(eventBase_ == nullptr || eventBase_->isInEventBaseThread());
541 if (callbacks_.empty()) {
542 // We can't actually begin accepting if no callbacks are defined.
543 // Wait until a callback is added to start accepting.
547 for (auto& handler : sockets_) {
548 if (!handler.registerHandler(
549 EventHandler::READ | EventHandler::PERSIST)) {
550 throw std::runtime_error("failed to register for accept events");
555 void AsyncServerSocket::pauseAccepting() {
556 assert(eventBase_ == nullptr || eventBase_->isInEventBaseThread());
558 for (auto& handler : sockets_) {
559 handler. unregisterHandler();
562 // If we were in the accept backoff state, disable the backoff timeout
563 if (backoffTimeout_) {
564 backoffTimeout_->cancelTimeout();
568 int AsyncServerSocket::createSocket(int family) {
569 int fd = socket(family, SOCK_STREAM, 0);
571 folly::throwSystemError(errno, "error creating async server socket");
583 void AsyncServerSocket::setupSocket(int fd) {
584 // Get the address family
585 SocketAddress address;
586 address.setFromLocalAddress(fd);
587 auto family = address.getFamily();
589 // Put the socket in non-blocking mode
590 if (fcntl(fd, F_SETFL, O_NONBLOCK) != 0) {
591 folly::throwSystemError(errno,
592 "failed to put socket in non-blocking mode");
595 // Set reuseaddr to avoid 2MSL delay on server restart
597 if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)) != 0) {
598 // This isn't a fatal error; just log an error message and continue
599 LOG(ERROR) << "failed to set SO_REUSEADDR on async server socket " << errno;
602 // Set reuseport to support multiple accept threads
604 if (reusePortEnabled_ &&
605 setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &one, sizeof(int)) != 0) {
606 LOG(ERROR) << "failed to set SO_REUSEPORT on async server socket "
608 folly::throwSystemError(errno,
609 "failed to bind to async server socket: " +
613 // Set keepalive as desired
614 if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE,
615 (keepAliveEnabled_) ? &one : &zero, sizeof(int)) != 0) {
616 LOG(ERROR) << "failed to set SO_KEEPALIVE on async server socket: " <<
620 // Setup FD_CLOEXEC flag
622 (-1 == folly::setCloseOnExec(fd, closeOnExec_))) {
623 LOG(ERROR) << "failed to set FD_CLOEXEC on async server socket: " <<
627 // Set TCP nodelay if available, MAC OS X Hack
628 // See http://lists.danga.com/pipermail/memcached/2005-March/001240.html
630 if (family != AF_UNIX) {
631 if (setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &one, sizeof(one)) != 0) {
632 // This isn't a fatal error; just log an error message and continue
633 LOG(ERROR) << "failed to set TCP_NODELAY on async server socket: " <<
639 if (shutdownSocketSet_) {
640 shutdownSocketSet_->add(fd);
644 void AsyncServerSocket::handlerReady(
645 uint16_t events, int fd, sa_family_t addressFamily) noexcept {
646 assert(!callbacks_.empty());
647 DestructorGuard dg(this);
649 // Only accept up to maxAcceptAtOnce_ connections at a time,
650 // to avoid starving other I/O handlers using this EventBase.
651 for (uint32_t n = 0; n < maxAcceptAtOnce_; ++n) {
652 SocketAddress address;
654 sockaddr_storage addrStorage;
655 socklen_t addrLen = sizeof(addrStorage);
656 sockaddr* saddr = reinterpret_cast<sockaddr*>(&addrStorage);
658 // In some cases, accept() doesn't seem to update these correctly.
659 saddr->sa_family = addressFamily;
660 if (addressFamily == AF_UNIX) {
661 addrLen = sizeof(struct sockaddr_un);
664 // Accept a new client socket
666 int clientSocket = accept4(fd, saddr, &addrLen, SOCK_NONBLOCK);
668 int clientSocket = accept(fd, saddr, &addrLen);
671 address.setFromSockaddr(saddr, addrLen);
673 std::chrono::time_point<std::chrono::steady_clock> nowMs =
674 std::chrono::steady_clock::now();
675 int64_t timeSinceLastAccept = std::max(
677 nowMs.time_since_epoch().count() -
678 lastAccepTimestamp_.time_since_epoch().count());
679 lastAccepTimestamp_ = nowMs;
680 if (acceptRate_ < 1) {
681 acceptRate_ *= 1 + acceptRateAdjustSpeed_ * timeSinceLastAccept;
682 if (acceptRate_ >= 1) {
684 } else if (rand() > acceptRate_ * RAND_MAX) {
685 ++numDroppedConnections_;
686 if (clientSocket >= 0) {
687 ::close(clientSocket);
693 if (clientSocket < 0) {
694 if (errno == EAGAIN) {
695 // No more sockets to accept right now.
696 // Check for this code first, since it's the most common.
698 } else if (errno == EMFILE || errno == ENFILE) {
699 // We're out of file descriptors. Perhaps we're accepting connections
700 // too quickly. Pause accepting briefly to back off and give the server
701 // a chance to recover.
702 LOG(ERROR) << "accept failed: out of file descriptors; entering accept "
706 // Dispatch the error message
707 dispatchError("accept() failed", errno);
709 dispatchError("accept() failed", errno);
714 #ifndef SOCK_NONBLOCK
715 // Explicitly set the new connection to non-blocking mode
716 if (fcntl(clientSocket, F_SETFL, O_NONBLOCK) != 0) {
717 ::close(clientSocket);
718 dispatchError("failed to set accepted socket to non-blocking mode",
724 // Inform the callback about the new connection
725 dispatchSocket(clientSocket, std::move(address));
727 // If we aren't accepting any more, break out of the loop
728 if (!accepting_ || callbacks_.empty()) {
734 void AsyncServerSocket::dispatchSocket(int socket,
735 SocketAddress&& address) {
736 uint32_t startingIndex = callbackIndex_;
738 // Short circuit if the callback is in the primary EventBase thread
740 CallbackInfo *info = nextCallback();
741 if (info->eventBase == nullptr) {
742 info->callback->connectionAccepted(socket, address);
746 // Create a message to send over the notification queue
748 msg.type = MessageType::MSG_NEW_CONN;
749 msg.address = std::move(address);
752 // Loop until we find a free queue to write to
754 if (info->consumer->getQueue()->tryPutMessageNoThrow(std::move(msg))) {
759 // We couldn't add to queue. Fall through to below
761 ++numDroppedConnections_;
762 if (acceptRateAdjustSpeed_ > 0) {
763 // aggressively decrease accept rate when in trouble
764 static const double kAcceptRateDecreaseSpeed = 0.1;
765 acceptRate_ *= 1 - kAcceptRateDecreaseSpeed;
769 if (callbackIndex_ == startingIndex) {
770 // The notification queue was full
771 // We can't really do anything at this point other than close the socket.
773 // This should only happen if a user's service is behaving extremely
774 // badly and none of the EventBase threads are looping fast enough to
775 // process the incoming connections. If the service is overloaded, it
776 // should use pauseAccepting() to temporarily back off accepting new
777 // connections, before they reach the point where their threads can't
778 // even accept new messages.
779 LOG(ERROR) << "failed to dispatch newly accepted socket:"
780 << " all accept callback queues are full";
785 info = nextCallback();
789 void AsyncServerSocket::dispatchError(const char *msgstr, int errnoValue) {
790 uint32_t startingIndex = callbackIndex_;
791 CallbackInfo *info = nextCallback();
793 // Create a message to send over the notification queue
795 msg.type = MessageType::MSG_ERROR;
796 msg.err = errnoValue;
797 msg.msg = std::move(msgstr);
800 // Short circuit if the callback is in the primary EventBase thread
801 if (info->eventBase == nullptr) {
802 std::runtime_error ex(
803 std::string(msgstr) + folly::to<std::string>(errnoValue));
804 info->callback->acceptError(ex);
808 if (info->consumer->getQueue()->tryPutMessageNoThrow(std::move(msg))) {
811 // Fall through and try another callback
813 if (callbackIndex_ == startingIndex) {
814 // The notification queues for all of the callbacks were full.
815 // We can't really do anything at this point.
816 LOG(ERROR) << "failed to dispatch accept error: all accept callback "
817 "queues are full: error msg: " <<
818 msg.msg.c_str() << errnoValue;
821 info = nextCallback();
825 void AsyncServerSocket::enterBackoff() {
826 // If this is the first time we have entered the backoff state,
827 // allocate backoffTimeout_.
828 if (backoffTimeout_ == nullptr) {
830 backoffTimeout_ = new BackoffTimeout(this);
831 } catch (const std::bad_alloc& ex) {
832 // Man, we couldn't even allocate the timer to re-enable accepts.
833 // We must be in pretty bad shape. Don't pause accepting for now,
834 // since we won't be able to re-enable ourselves later.
835 LOG(ERROR) << "failed to allocate AsyncServerSocket backoff"
836 << " timer; unable to temporarly pause accepting";
841 // For now, we simply pause accepting for 1 second.
843 // We could add some smarter backoff calculation here in the future. (e.g.,
844 // start sleeping for longer if we keep hitting the backoff frequently.)
845 // Typically the user needs to figure out why the server is overloaded and
846 // fix it in some other way, though. The backoff timer is just a simple
847 // mechanism to try and give the connection processing code a little bit of
848 // breathing room to catch up, and to avoid just spinning and failing to
849 // accept over and over again.
850 const uint32_t timeoutMS = 1000;
851 if (!backoffTimeout_->scheduleTimeout(timeoutMS)) {
852 LOG(ERROR) << "failed to schedule AsyncServerSocket backoff timer;"
853 << "unable to temporarly pause accepting";
857 // The backoff timer is scheduled to re-enable accepts.
858 // Go ahead and disable accepts for now. We leave accepting_ set to true,
859 // since that tracks the desired state requested by the user.
860 for (auto& handler : sockets_) {
861 handler.unregisterHandler();
865 void AsyncServerSocket::backoffTimeoutExpired() {
866 // accepting_ should still be true.
867 // If pauseAccepting() was called while in the backoff state it will cancel
868 // the backoff timeout.
870 // We can't be detached from the EventBase without being paused
871 assert(eventBase_ != nullptr && eventBase_->isInEventBaseThread());
873 // If all of the callbacks were removed, we shouldn't re-enable accepts
874 if (callbacks_.empty()) {
878 // Register the handler.
879 for (auto& handler : sockets_) {
880 if (!handler.registerHandler(
881 EventHandler::READ | EventHandler::PERSIST)) {
882 // We're hosed. We could just re-schedule backoffTimeout_ to
883 // re-try again after a little bit. However, we don't want to
884 // loop retrying forever if we can't re-enable accepts. Just
885 // abort the entire program in this state; things are really bad
886 // and restarting the entire server is probably the best remedy.
888 << "failed to re-enable AsyncServerSocket accepts after backoff; "