Initial source checkin.

The source files were determined by building net_unittests in chromium's source
tree. Some of the obvious libraries were left out (v8, gmock, gtest).

The Android.mk file has all the sources (minus unittests and tools) that were
used during net_unittests compilation. Nothing builds yet because of STL but
that is the next task. The .cpp files will most likely not compile anyways
because of the LOCAL_CPP_EXTENSION mod. I will have to break this into multiple
projects to get around that limitation.

1 files changed, 814 insertions, 0 deletions

diff --git a/net/tools/flip_server/epoll_server.cc b/net/tools/flip_server/epoll_server.cc
new file mode 100644
index 0000000..a1d6ca1
--- /dev/null
+++ b/net/tools/flip_server/epoll_server.cc
@@ -0,0 +1,814 @@
+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/tools/flip_server/epoll_server.h"
+
+#include <stdlib.h>  // for abort
+#include <errno.h>    // for errno and strerror_r
+#include <algorithm>
+#include <iostream>
+#include <utility>
+#include <vector>
+
+#include "base/logging.h"
+#include "base/timer.h"
+#include "net/tools/flip_server/other_defines.h"
+
+// Design notes: An efficient implementation of ready list has the following
+// desirable properties:
+//
+// A. O(1) insertion into/removal from the list in any location.
+// B. Once the callback is found by hash lookup using the fd, the lookup of
+//    corresponding entry in the list is O(1).
+// C. Safe insertion into/removal from the list during list iteration. (The
+//    ready list's purpose is to enable completely event driven I/O model.
+//    Thus, all the interesting bits happen in the callback. It is critical
+//    to not place any restriction on the API during list iteration.
+//
+// The current implementation achieves these goals with the following design:
+//
+// - The ready list is constructed as a doubly linked list to enable O(1)
+//   insertion/removal (see man 3 queue).
+// - The forward and backward links are directly embedded inside the
+//   CBAndEventMask struct. This enables O(1) lookup in the list for a given
+//   callback. (Techincally, we could've used std::list of hash_set::iterator,
+//   and keep a list::iterator in CBAndEventMask to achieve the same effect.
+//   However, iterators have two problems: no way to portably invalidate them,
+//   and no way to tell whether an iterator is singular or not. The only way to
+//   overcome these issues is to keep bools in both places, but that throws off
+//   memory alignment (up to 7 wasted bytes for each bool). The extra level of
+//   indirection will also likely be less cache friendly. Direct manipulation
+//   of link pointers makes it easier to retrieve the CBAndEventMask from the
+//   list, easier to check whether an CBAndEventMask is in the list, uses less
+//   memory (save 32 bytes/fd), and does not affect cache usage (we need to
+//   read in the struct to use the callback anyway).)
+// - Embed the fd directly into CBAndEventMask and switch to using hash_set.
+//   This removes the need to store hash_map::iterator in the list just so that
+//   we can get both the fd and the callback.
+// - The ready list is "one shot": each entry is removed before OnEvent is
+//   called. This removes the mutation-while-iterating problem.
+// - Use two lists to keep track of callbacks. The ready_list_ is the one used
+//   for registration. Before iteration, the ready_list_ is swapped into the
+//   tmp_list_. Once iteration is done, tmp_list_ will be empty, and
+//   ready_list_ will have all the new ready fds.
+
+// The size we use for buffers passed to strerror_r
+static const int kErrorBufferSize = 256;
+
+namespace net {
+
+// Clears the pipe and returns.  Used for waking the epoll server up.
+class ReadPipeCallback : public EpollCallbackInterface {
+ public:
+  void OnEvent(int fd, EpollEvent* event) {
+    DCHECK(event->in_events == EPOLLIN);
+    int data;
+    int data_read = 1;
+    // Read until the pipe is empty.
+    while (data_read > 0) {
+      data_read = read(fd, &data, sizeof(data));
+    }
+  }
+  void OnShutdown(EpollServer *eps, int fd) {}
+  void OnRegistration(EpollServer*, int, int) {}
+  void OnModification(int, int) {}       // COV_NF_LINE
+  void OnUnregistration(int, bool) {}    // COV_NF_LINE
+};
+
+////////////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////////////
+
+EpollServer::EpollServer()
+  : epoll_fd_(epoll_create(1024)),
+    timeout_in_us_(0),
+    recorded_now_in_us_(0),
+    ready_list_size_(0),
+    wake_cb_(new ReadPipeCallback),
+    read_fd_(-1),
+    write_fd_(-1),
+    in_wait_for_events_and_execute_callbacks_(false),
+    in_shutdown_(false) {
+  // ensure that the epoll_fd_ is valid.
+  CHECK_NE(epoll_fd_, -1);
+  LIST_INIT(&ready_list_);
+  LIST_INIT(&tmp_list_);
+
+  int pipe_fds[2];
+  if (pipe(pipe_fds) < 0) {
+    // Unfortunately, it is impossible to test any such initialization in
+    // a constructor (as virtual methods do not yet work).
+    // This -could- be solved by moving initialization to an outside
+    // call...
+    int saved_errno = errno;
+    char buf[kErrorBufferSize];
+    LOG(FATAL) << "Error " << saved_errno
+               << " in pipe(): " << strerror_r(saved_errno, buf, sizeof(buf));
+  }
+  read_fd_ = pipe_fds[0];
+  write_fd_ = pipe_fds[1];
+  RegisterFD(read_fd_, wake_cb_.get(), EPOLLIN);
+}
+
+void EpollServer::CleanupFDToCBMap() {
+  FDToCBMap::iterator cb_iter = cb_map_.begin();
+  while (cb_iter != cb_map_.end()) {
+    int fd = cb_iter->fd;
+    CB* cb = cb_iter->cb;
+
+    cb_iter->in_use = true;
+    if (cb) {
+      cb->OnShutdown(this, fd);
+    }
+
+    cb_map_.erase(cb_iter);
+    cb_iter = cb_map_.begin();
+  }
+}
+
+void EpollServer::CleanupTimeToAlarmCBMap() {
+  TimeToAlarmCBMap::iterator erase_it;
+
+  // Call OnShutdown() on alarms. Note that the structure of the loop
+  // is similar to the structure of loop in the function HandleAlarms()
+  for (TimeToAlarmCBMap::iterator i = alarm_map_.begin();
+       i != alarm_map_.end();
+      ) {
+    // Note that OnShutdown() can call UnregisterAlarm() on
+    // other iterators. OnShutdown() should not call UnregisterAlarm()
+    // on self because by definition the iterator is not valid any more.
+    i->second->OnShutdown(this);
+    erase_it = i;
+    ++i;
+    alarm_map_.erase(erase_it);
+  }
+}
+
+EpollServer::~EpollServer() {
+  DCHECK_EQ(in_shutdown_, false);
+  in_shutdown_ = true;
+#ifdef EPOLL_SERVER_EVENT_TRACING
+  LOG(INFO) << "\n" << event_recorder_;
+#endif
+  VLOG(2) << "Shutting down epoll server ";
+  CleanupFDToCBMap();
+
+  LIST_INIT(&ready_list_);
+  LIST_INIT(&tmp_list_);
+
+  CleanupTimeToAlarmCBMap();
+
+  close(read_fd_);
+  close(write_fd_);
+  close(epoll_fd_);
+}
+
+// Whether a CBAandEventMask is on the ready list is determined by a non-NULL
+// le_prev pointer (le_next being NULL indicates end of list).
+inline void EpollServer::AddToReadyList(CBAndEventMask* cb_and_mask) {
+  if (cb_and_mask->entry.le_prev == NULL) {
+    LIST_INSERT_HEAD(&ready_list_, cb_and_mask, entry);
+    ++ready_list_size_;
+  }
+}
+
+inline void EpollServer::RemoveFromReadyList(
+    const CBAndEventMask& cb_and_mask) {
+  if (cb_and_mask.entry.le_prev != NULL) {
+    LIST_REMOVE(&cb_and_mask, entry);
+    // Clean up all the ready list states. Don't bother with the other fields
+    // as they are initialized when the CBAandEventMask is added to the ready
+    // list. This saves a few cycles in the inner loop.
+    cb_and_mask.entry.le_prev = NULL;
+    --ready_list_size_;
+    if (ready_list_size_ == 0) {
+      DCHECK(ready_list_.lh_first == NULL);
+      DCHECK(tmp_list_.lh_first == NULL);
+    }
+  }
+}
+
+void EpollServer::RegisterFD(int fd, CB* cb, int event_mask) {
+  CHECK(cb);
+  VLOG(3) << "RegisterFD fd=" << fd << " event_mask=" << event_mask;
+  FDToCBMap::iterator fd_i = cb_map_.find(CBAndEventMask(NULL, 0, fd));
+  if (cb_map_.end() != fd_i) {
+    // do we just abort, or do we just unregister the other guy?
+    // for now, lets just unregister the other guy.
+
+    // unregister any callback that may already be registered for this FD.
+    CB* other_cb = fd_i->cb;
+    if (other_cb) {
+      // Must remove from the ready list before erasing.
+      RemoveFromReadyList(*fd_i);
+      other_cb->OnUnregistration(fd, true);
+      ModFD(fd, event_mask);
+    } else {
+      // already unregistered, so just recycle the node.
+      AddFD(fd, event_mask);
+    }
+    fd_i->cb = cb;
+    fd_i->event_mask = event_mask;
+    fd_i->events_to_fake = 0;
+  } else {
+    AddFD(fd, event_mask);
+    cb_map_.insert(CBAndEventMask(cb, event_mask, fd));
+  }
+
+
+  // set the FD to be non-blocking.
+  SetNonblocking(fd);
+
+  cb->OnRegistration(this, fd, event_mask);
+}
+
+void EpollServer::SetNonblocking(int fd) {
+  int flags = GetFlags(fd);
+  if (flags == -1) {
+    int saved_errno = errno;
+    char buf[kErrorBufferSize];
+    LOG(FATAL) << "Error " << saved_errno
+               << " doing fcntl(" << fd << ", F_GETFL, 0): "
+               << strerror_r(saved_errno, buf, sizeof(buf));
+  }
+  if (!(flags & O_NONBLOCK)) {
+    int saved_flags = flags;
+    flags = SetFlags(fd, flags | O_NONBLOCK);
+    if (flags == -1) {
+      // bad.
+      int saved_errno = errno;
+      char buf[kErrorBufferSize];
+      LOG(FATAL) << "Error " << saved_errno
+        << " doing fcntl(" << fd << ", F_SETFL, " << saved_flags << "): "
+        << strerror_r(saved_errno, buf, sizeof(buf));
+    }
+  }
+}
+
+void EpollServer::RegisterFDForWrite(int fd, CB* cb) {
+  RegisterFD(fd, cb, EPOLLOUT);
+}
+
+void EpollServer::RegisterFDForReadWrite(int fd, CB* cb) {
+  RegisterFD(fd, cb, EPOLLIN | EPOLLOUT);
+}
+
+void EpollServer::RegisterFDForRead(int fd, CB* cb) {
+  RegisterFD(fd, cb, EPOLLIN);
+}
+
+void EpollServer::UnregisterFD(int fd) {
+  FDToCBMap::iterator fd_i = cb_map_.find(CBAndEventMask(NULL, 0, fd));
+  if (cb_map_.end() == fd_i || fd_i->cb == NULL) {
+    // Doesn't exist in server, or has gone through UnregisterFD once and still
+    // inside the callchain of OnEvent.
+    return;
+  }
+#ifdef EPOLL_SERVER_EVENT_TRACING
+  event_recorder_.RecordUnregistration(fd);
+#endif
+  CB* cb = fd_i->cb;
+  // Since the links are embedded within the struct, we must remove it from the
+  // list before erasing it from the hash_set.
+  RemoveFromReadyList(*fd_i);
+  DelFD(fd);
+  cb->OnUnregistration(fd, false);
+  // fd_i->cb is NULL if that fd is unregistered inside the callchain of
+  // OnEvent. Since the EpollServer needs a valid CBAndEventMask after OnEvent
+  // returns in order to add it to the ready list, we cannot have UnregisterFD
+  // erase the entry if it is in use. Thus, a NULL fd_i->cb is used as a
+  // condition that tells the EpollServer that this entry is unused at a later
+  // point.
+  if (!fd_i->in_use) {
+    cb_map_.erase(fd_i);
+  } else {
+    // Remove all trace of the registration, and just keep the node alive long
+    // enough so the code that calls OnEvent doesn't have to worry about
+    // figuring out whether the CBAndEventMask is valid or not.
+    fd_i->cb = NULL;
+    fd_i->event_mask = 0;
+    fd_i->events_to_fake = 0;
+  }
+}
+
+void EpollServer::ModifyCallback(int fd, int event_mask) {
+  ModifyFD(fd, ~0, event_mask);
+}
+
+void EpollServer::StopRead(int fd) {
+  ModifyFD(fd, EPOLLIN, 0);
+}
+
+void EpollServer::StartRead(int fd) {
+  ModifyFD(fd, 0, EPOLLIN);
+}
+
+void EpollServer::StopWrite(int fd) {
+  ModifyFD(fd, EPOLLOUT, 0);
+}
+
+void EpollServer::StartWrite(int fd) {
+  ModifyFD(fd, 0, EPOLLOUT);
+}
+
+void EpollServer::HandleEvent(int fd, int event_mask) {
+#ifdef EPOLL_SERVER_EVENT_TRACING
+  event_recorder_.RecordEpollEvent(fd, event_mask);
+#endif
+  FDToCBMap::iterator fd_i = cb_map_.find(CBAndEventMask(NULL, 0, fd));
+  if (fd_i == cb_map_.end() || fd_i->cb == NULL) {
+    // Ignore the event.
+    // This could occur if epoll() returns a set of events, and
+    // while processing event A (earlier) we removed the callback
+    // for event B (and are now processing event B).
+    return;
+  }
+  fd_i->events_asserted = event_mask;
+  CBAndEventMask* cb_and_mask = const_cast<CBAndEventMask*>(&*fd_i);
+  AddToReadyList(cb_and_mask);
+}
+
+class TrueFalseGuard {
+ public:
+  explicit TrueFalseGuard(bool* guarded_bool) : guarded_bool_(guarded_bool) {
+    DCHECK(guarded_bool_ != NULL);
+    DCHECK(*guarded_bool_ == false);
+    *guarded_bool_ = true;
+  }
+  ~TrueFalseGuard() {
+    *guarded_bool_ = false;
+  }
+ private:
+  bool* guarded_bool_;
+};
+
+void EpollServer::WaitForEventsAndExecuteCallbacks() {
+  if (in_wait_for_events_and_execute_callbacks_) {
+    LOG(DFATAL) <<
+      "Attempting to call WaitForEventsAndExecuteCallbacks"
+      " when an ancestor to the current function is already"
+      " WaitForEventsAndExecuteCallbacks!";
+    // The line below is actually tested, but in coverage mode,
+    // we never see it.
+    return;  // COV_NF_LINE
+  }
+  TrueFalseGuard recursion_guard(&in_wait_for_events_and_execute_callbacks_);
+  if (alarm_map_.empty()) {
+    // no alarms, this is business as usual.
+    WaitForEventsAndCallHandleEvents(timeout_in_us_,
+                                     events_,
+                                     events_size_);
+    recorded_now_in_us_ = 0;
+    return;
+  }
+
+  // store the 'now'. If we recomputed 'now' every iteration
+  // down below, then we might never exit that loop-- any
+  // long-running alarms might install other long-running
+  // alarms, etc. By storing it here now, we ensure that
+  // a more reasonable amount of work is done here.
+  int64 now_in_us  = NowInUsec();
+
+  // Get the first timeout from the alarm_map where it is
+  // stored in absolute time.
+  int64 next_alarm_time_in_us =  alarm_map_.begin()->first;
+  VLOG(4) << "next_alarm_time = " << next_alarm_time_in_us
+          << " now             = " << now_in_us
+          << " timeout_in_us = " << timeout_in_us_;
+
+  int64 wait_time_in_us;
+  int64 alarm_timeout_in_us = next_alarm_time_in_us - now_in_us;
+
+  // If the next alarm is sooner than the default timeout, or if there is no
+  // timeout (timeout_in_us_ == -1), wake up when the alarm should fire.
+  // Otherwise use the default timeout.
+  if (alarm_timeout_in_us < timeout_in_us_ || timeout_in_us_ < 0) {
+    wait_time_in_us = std::max(alarm_timeout_in_us, static_cast<int64>(0));
+  } else {
+    wait_time_in_us = timeout_in_us_;
+  }
+
+  VLOG(4) << "wait_time_in_us = " << wait_time_in_us;
+
+  // wait for events.
+
+  WaitForEventsAndCallHandleEvents(wait_time_in_us,
+                                   events_,
+                                   events_size_);
+  CallAndReregisterAlarmEvents();
+  recorded_now_in_us_ = 0;
+}
+
+void EpollServer::SetFDReady(int fd, int events_to_fake) {
+  FDToCBMap::iterator fd_i = cb_map_.find(CBAndEventMask(NULL, 0, fd));
+  if (cb_map_.end() != fd_i && fd_i->cb != NULL) {
+    // This const_cast is necessary for LIST_HEAD_INSERT to work. Declaring
+    // entry mutable is insufficient because LIST_HEAD_INSERT assigns the
+    // forward pointer of the list head to the current cb_and_mask, and the
+    // compiler complains that it can't assign a const T* to a T*.
+    CBAndEventMask* cb_and_mask = const_cast<CBAndEventMask*>(&*fd_i);
+    // Note that there is no clearly correct behavior here when
+    // cb_and_mask->events_to_fake != 0 and this function is called.
+    // Of the two operations:
+    //      cb_and_mask->events_to_fake = events_to_fake
+    //      cb_and_mask->events_to_fake |= events_to_fake
+    // the first was picked because it discourages users from calling
+    // SetFDReady repeatedly to build up the correct event set as it is more
+    // efficient to call SetFDReady once with the correct, final mask.
+    cb_and_mask->events_to_fake = events_to_fake;
+    AddToReadyList(cb_and_mask);
+  }
+}
+
+void EpollServer::SetFDNotReady(int fd) {
+  FDToCBMap::iterator fd_i = cb_map_.find(CBAndEventMask(NULL, 0, fd));
+  if (cb_map_.end() != fd_i) {
+    RemoveFromReadyList(*fd_i);
+  }
+}
+
+bool EpollServer::IsFDReady(int fd) const {
+  FDToCBMap::const_iterator fd_i = cb_map_.find(CBAndEventMask(NULL, 0, fd));
+  return (cb_map_.end() != fd_i &&
+          fd_i->cb != NULL &&
+          fd_i->entry.le_prev != NULL);
+}
+
+void EpollServer::VerifyReadyList() const {
+  int count = 0;
+  CBAndEventMask* cur = ready_list_.lh_first;
+  for (; cur; cur = cur->entry.le_next) {
+    ++count;
+  }
+  for (cur = tmp_list_.lh_first; cur; cur = cur->entry.le_next) {
+    ++count;
+  }
+  CHECK_EQ(ready_list_size_, count) << "Ready list size does not match count";
+}
+
+void EpollServer::RegisterAlarm(int64 timeout_time_in_us, AlarmCB* ac) {
+  CHECK(ac);
+  if (ContainsAlarm(ac)) {
+    LOG(FATAL) << "Alarm already exists " << ac;
+  }
+  VLOG(4) << "RegisteringAlarm at : " << timeout_time_in_us;
+
+  TimeToAlarmCBMap::iterator alarm_iter =
+      alarm_map_.insert(std::make_pair(timeout_time_in_us, ac));
+
+  all_alarms_.insert(ac);
+  // Pass the iterator to the EpollAlarmCallbackInterface.
+  ac->OnRegistration(alarm_iter, this);
+}
+
+// Unregister a specific alarm callback: iterator_token must be a
+//  valid iterator. The caller must ensure the validity of the iterator.
+void EpollServer::UnregisterAlarm(const AlarmRegToken& iterator_token) {
+  AlarmCB* cb = iterator_token->second;
+  alarm_map_.erase(iterator_token);
+  all_alarms_.erase(cb);
+  cb->OnUnregistration();
+}
+
+int EpollServer::NumFDsRegistered() const {
+  DCHECK(cb_map_.size() >= 1);
+  // Omit the internal FD (read_fd_)
+  return cb_map_.size() - 1;
+}
+
+void EpollServer::Wake() {
+  char data = 'd';  // 'd' is for data.  It's good enough for me.
+  write(write_fd_, &data, 1);
+}
+
+int64 EpollServer::NowInUsec() const {
+  return base::Time::Now().ToInternalValue();
+}
+
+std::string EpollServer::EventMaskToString(int event_mask) {
+  std::string s;
+  if (event_mask & EPOLLIN) s += "EPOLLIN ";
+  if (event_mask & EPOLLPRI) s += "EPOLLPRI ";
+  if (event_mask & EPOLLOUT) s += "EPOLLOUT ";
+  if (event_mask & EPOLLRDNORM) s += "EPOLLRDNORM ";
+  if (event_mask & EPOLLRDBAND) s += "EPOLLRDBAND ";
+  if (event_mask & EPOLLWRNORM) s += "EPOLLWRNORM ";
+  if (event_mask & EPOLLWRBAND) s += "EPOLLWRBAND ";
+  if (event_mask & EPOLLMSG) s += "EPOLLMSG ";
+  if (event_mask & EPOLLERR) s += "EPOLLERR ";
+  if (event_mask & EPOLLHUP) s += "EPOLLHUP ";
+  if (event_mask & EPOLLONESHOT) s += "EPOLLONESHOT ";
+  if (event_mask & EPOLLET) s += "EPOLLET ";
+  return s;
+}
+
+void EpollServer::LogStateOnCrash() {
+  LOG(ERROR) << "----------------------Epoll Server---------------------------";
+  LOG(ERROR) << "Epoll server " << this << " polling on fd " << epoll_fd_;
+  LOG(ERROR) << "timeout_in_us_: " << timeout_in_us_;
+
+  // Log sessions with alarms.
+  LOG(ERROR) << alarm_map_.size() << " alarms registered.";
+  for (TimeToAlarmCBMap::iterator it = alarm_map_.begin();
+       it != alarm_map_.end();
+       ++it) {
+    const bool skipped =
+        alarms_reregistered_and_should_be_skipped_.find(it->second)
+        != alarms_reregistered_and_should_be_skipped_.end();
+    LOG(ERROR) << "Alarm " << it->second << " registered at time " << it->first
+               << " and should be skipped = " << skipped;
+  }
+
+  LOG(ERROR) << cb_map_.size() << " fd callbacks registered.";
+  for (FDToCBMap::iterator it = cb_map_.begin();
+       it != cb_map_.end();
+       ++it) {
+    LOG(ERROR) << "fd: " << it->fd << " with mask " << it->event_mask
+               << " registered with cb: " << it->cb;
+  }
+  LOG(ERROR) << "----------------------/Epoll Server--------------------------";
+}
+
+
+
+////////////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////////////
+
+void EpollServer::DelFD(int fd) const {
+  struct epoll_event ee;
+  memset(&ee, 0, sizeof(ee));
+#ifdef EPOLL_SERVER_EVENT_TRACING
+  event_recorder_.RecordFDMaskEvent(fd, 0, "DelFD");
+#endif
+  if (epoll_ctl(epoll_fd_, EPOLL_CTL_DEL, fd, &ee)) {
+    int saved_errno = errno;
+    char buf[kErrorBufferSize];
+    LOG(FATAL) << "Epoll set removal error for fd " << fd << ": "
+               << strerror_r(saved_errno, buf, sizeof(buf));
+  }
+}
+
+////////////////////////////////////////
+
+void EpollServer::AddFD(int fd, int event_mask) const {
+  struct epoll_event ee;
+  memset(&ee, 0, sizeof(ee));
+  ee.events = event_mask | EPOLLERR | EPOLLHUP;
+  ee.data.fd = fd;
+#ifdef EPOLL_SERVER_EVENT_TRACING
+  event_recorder_.RecordFDMaskEvent(fd, ee.events, "AddFD");
+#endif
+  if (epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, fd, &ee)) {
+    int saved_errno = errno;
+    char buf[kErrorBufferSize];
+    LOG(FATAL) << "Epoll set insertion error for fd " << fd << ": "
+               << strerror_r(saved_errno, buf, sizeof(buf));
+  }
+}
+
+////////////////////////////////////////
+
+void EpollServer::ModFD(int fd, int event_mask) const {
+  struct epoll_event ee;
+  memset(&ee, 0, sizeof(ee));
+  ee.events = event_mask | EPOLLERR | EPOLLHUP;
+  ee.data.fd = fd;
+#ifdef EPOLL_SERVER_EVENT_TRACING
+  event_recorder_.RecordFDMaskEvent(fd, ee.events, "ModFD");
+#endif
+  VLOG(3) <<  "modifying fd= " << fd << " "
+          << EventMaskToString(ee.events);
+  if (epoll_ctl(epoll_fd_, EPOLL_CTL_MOD, fd, &ee)) {
+    int saved_errno = errno;
+    char buf[kErrorBufferSize];
+    LOG(FATAL) << "Epoll set modification error for fd " << fd << ": "
+               << strerror_r(saved_errno, buf, sizeof(buf));
+  }
+}
+
+////////////////////////////////////////
+
+void EpollServer::ModifyFD(int fd, int remove_event, int add_event) {
+  FDToCBMap::iterator fd_i = cb_map_.find(CBAndEventMask(NULL, 0, fd));
+  if (cb_map_.end() == fd_i) {
+    VLOG(2) << "Didn't find the fd " << fd << "in internal structures";
+    return;
+  }
+
+  if (fd_i->cb != NULL) {
+    int & event_mask = fd_i->event_mask;
+    VLOG(3) << "fd= " << fd
+            << " event_mask before: " << EventMaskToString(event_mask);
+    event_mask &= ~remove_event;
+    event_mask |= add_event;
+
+    VLOG(3) << " event_mask after: " << EventMaskToString(event_mask);
+
+    ModFD(fd, event_mask);
+
+    fd_i->cb->OnModification(fd, event_mask);
+  }
+}
+
+void EpollServer::WaitForEventsAndCallHandleEvents(int64 timeout_in_us,
+                                                   struct epoll_event events[],
+                                                   int events_size) {
+  if (timeout_in_us == 0 || ready_list_.lh_first != NULL) {
+    // If ready list is not empty, then don't sleep at all.
+    timeout_in_us = 0;
+  } else if (timeout_in_us < 0) {
+    LOG(INFO) << "Negative epoll timeout: " << timeout_in_us
+              << "us; epoll will wait forever for events.";
+    // If timeout_in_us is < 0 we are supposed to Wait forever.  This means we
+    // should set timeout_in_us to -1000 so we will
+    // Wait(-1000/1000) == Wait(-1) == Wait forever.
+    timeout_in_us = -1000;
+  } else {
+    // If timeout is specified, and the ready list is empty.
+    if (timeout_in_us < 1000) {
+      timeout_in_us = 1000;
+    }
+  }
+  const int timeout_in_ms = timeout_in_us / 1000;
+  int nfds = epoll_wait_impl(epoll_fd_,
+                             events,
+                             events_size,
+                             timeout_in_ms);
+  VLOG(3) << "nfds=" << nfds;
+
+#ifdef EPOLL_SERVER_EVENT_TRACING
+  event_recorder_.RecordEpollWaitEvent(timeout_in_ms, nfds);
+#endif
+
+  // If you're wondering why the NowInUsec() is recorded here, the answer is
+  // simple: If we did it before the epoll_wait_impl, then the max error for
+  // the ApproximateNowInUs() call would be as large as the maximum length of
+  // epoll_wait, which can be arbitrarily long. Since this would make
+  // ApproximateNowInUs() worthless, we instead record the time -after- we've
+  // done epoll_wait, which guarantees that the maximum error is the amount of
+  // time it takes to process all the events generated by epoll_wait.
+  recorded_now_in_us_ = NowInUsec();
+  if (nfds > 0) {
+    for (int i = 0; i < nfds; ++i) {
+      int event_mask = events[i].events;
+      int fd = events[i].data.fd;
+      HandleEvent(fd, event_mask);
+    }
+  } else if (nfds < 0) {
+    // Catch interrupted syscall and just ignore it and move on.
+    if (errno != EINTR && errno != 0) {
+      int saved_errno = errno;
+      char buf[kErrorBufferSize];
+      LOG(FATAL) << "Error " << saved_errno << " in epoll_wait: "
+                 << strerror_r(saved_errno, buf, sizeof(buf));
+    }
+  }
+
+  // Now run through the ready list.
+  if (ready_list_.lh_first) {
+    CallReadyListCallbacks();
+  }
+}
+
+void EpollServer::CallReadyListCallbacks() {
+  // Check pre-conditions.
+  DCHECK(tmp_list_.lh_first == NULL);
+  // Swap out the ready_list_ into the tmp_list_ before traversing the list to
+  // enable SetFDReady() to just push new items into the ready_list_.
+  std::swap(ready_list_.lh_first, tmp_list_.lh_first);
+  if (tmp_list_.lh_first) {
+    tmp_list_.lh_first->entry.le_prev = &tmp_list_.lh_first;
+    EpollEvent event(0, false);
+    while (tmp_list_.lh_first != NULL) {
+      DCHECK_GT(ready_list_size_, 0);
+      CBAndEventMask* cb_and_mask = tmp_list_.lh_first;
+      RemoveFromReadyList(*cb_and_mask);
+
+      event.out_ready_mask = 0;
+      event.in_events =
+        cb_and_mask->events_asserted | cb_and_mask->events_to_fake;
+      // TODO(fenix): get rid of the two separate fields in cb_and_mask.
+      cb_and_mask->events_asserted = 0;
+      cb_and_mask->events_to_fake = 0;
+      {
+        // OnEvent() may call UnRegister, so we set in_use, here. Any
+        // UnRegister call will now simply set the cb to NULL instead of
+        // invalidating the cb_and_mask object (by deleting the object in the
+        // map to which cb_and_mask refers)
+        TrueFalseGuard in_use_guard(&(cb_and_mask->in_use));
+        cb_and_mask->cb->OnEvent(cb_and_mask->fd, &event);
+      }
+
+      // Since OnEvent may have called UnregisterFD, we must check here that
+      // the callback is still valid. If it isn't, then UnregisterFD *was*
+      // called, and we should now get rid of the object.
+      if (cb_and_mask->cb == NULL) {
+        cb_map_.erase(*cb_and_mask);
+      } else if (event.out_ready_mask != 0) {
+        cb_and_mask->events_to_fake = event.out_ready_mask;
+        AddToReadyList(cb_and_mask);
+      }
+    }
+  }
+  DCHECK(tmp_list_.lh_first == NULL);
+}
+
+const int EpollServer::kMinimumEffectiveAlarmQuantum = 1000;
+
+// Alarms may be up to kMinimumEffectiveAlarmQuantum -1 us late.
+inline int64 EpollServer::DoRoundingOnNow(int64 now_in_us) const {
+  now_in_us /= kMinimumEffectiveAlarmQuantum;
+  now_in_us *= kMinimumEffectiveAlarmQuantum;
+  now_in_us += (2 * kMinimumEffectiveAlarmQuantum - 1);
+  return now_in_us;
+}
+
+void EpollServer::CallAndReregisterAlarmEvents() {
+  int64 now_in_us = recorded_now_in_us_;
+  DCHECK_NE(0, recorded_now_in_us_);
+  now_in_us = DoRoundingOnNow(now_in_us);
+
+  TimeToAlarmCBMap::iterator erase_it;
+
+  // execute alarms.
+  for (TimeToAlarmCBMap::iterator i = alarm_map_.begin();
+       i != alarm_map_.end();
+      ) {
+    if (i->first > now_in_us) {
+      break;
+    }
+    AlarmCB* cb = i->second;
+    // Execute the OnAlarm() only if we did not register
+    // it in this loop itself.
+    const bool added_in_this_round =
+        alarms_reregistered_and_should_be_skipped_.find(cb)
+        != alarms_reregistered_and_should_be_skipped_.end();
+    if (added_in_this_round) {
+      ++i;
+      continue;
+    }
+    all_alarms_.erase(cb);
+    const int64 new_timeout_time_in_us = cb->OnAlarm();
+
+    erase_it = i;
+    ++i;
+    alarm_map_.erase(erase_it);
+
+    if (new_timeout_time_in_us > 0) {
+      // We add to hash_set only if the new timeout is <= now_in_us.
+      // if timeout is > now_in_us then we have no fear that this alarm
+      // can be reexecuted in this loop, and hence we do not need to
+      // worry about a recursive loop.
+      DVLOG(3) << "Reregistering alarm "
+               << " " << cb
+               << " " << new_timeout_time_in_us
+               << " " << now_in_us;
+      if (new_timeout_time_in_us <= now_in_us) {
+        alarms_reregistered_and_should_be_skipped_.insert(cb);
+      }
+      RegisterAlarm(new_timeout_time_in_us, cb);
+    }
+  }
+  alarms_reregistered_and_should_be_skipped_.clear();
+}
+
+EpollAlarm::EpollAlarm() : eps_(NULL), registered_(false) {
+}
+
+EpollAlarm::~EpollAlarm() {
+  UnregisterIfRegistered();
+}
+
+int64 EpollAlarm::OnAlarm() {
+  registered_ = false;
+  return 0;
+}
+
+void EpollAlarm::OnRegistration(const EpollServer::AlarmRegToken& token,
+                                EpollServer* eps) {
+  DCHECK_EQ(false, registered_);
+
+  token_ = token;
+  eps_ = eps;
+  registered_ = true;
+}
+
+void EpollAlarm::OnUnregistration() {
+  registered_ = false;
+}
+
+void EpollAlarm::OnShutdown(EpollServer* eps) {
+  registered_ = false;
+  eps_ = NULL;
+}
+
+// If the alarm was registered, unregister it.
+void EpollAlarm::UnregisterIfRegistered() {
+  if (!registered_) {
+    return;
+  }
+  eps_->UnregisterAlarm(token_);
+}
+
+}  // namespace net
+