Issue 3595 - Get rid of detached threads for setTimeout

src/DefaultTimer.cpp

+/*
+* This file is part of Adblock Plus <https://adblockplus.org/>,
+* Copyright (C) 2006-2017 eyeo GmbH
+*
+* Adblock Plus is free software: you can redistribute it and/or modify
+* it under the terms of the GNU General Public License version 3 as
+* published by the Free Software Foundation.
+*
+* Adblock Plus is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "DefaultTimer.h"
+
+using AdblockPlus::DefaultTimer;
+
+DefaultTimer::DefaultTimer()
+  : shouldThreadStop(false)
+{
+  m_thread = std::thread([this]
+  {
+    ThreadFunc();
+  });
+}
+
+DefaultTimer::~DefaultTimer()
+{
+  shouldThreadStop = true;
+  conditionVariable.notify_one();
+  if (m_thread.joinable())
+    m_thread.join();
+}
+
+void DefaultTimer::SetTimer(const std::chrono::milliseconds& timeout, const TimerCallback& timerCallback)
+{
+  if (!timerCallback)
+    return;
+  std::lock_guard<std::mutex> lock(mutex);

[Oleksandr, 2017/03/28 10:39:55]

If there's already a timer for let's say 1 minute the SetTimer call would just
hang for 1 minute here, right? I don't think that's acceptable.

[sergei, 2017/03/28 11:06:59]

No, `conditionVariable.wait(lock,...` and `conditionVariable.wait_until(lock,`
in `DefaultTimer::ThreadFunc` "unlock" the mutex, so one can add timers.

[Oleksandr, 2017/03/28 11:11:00]

Fair enough.

+  TimerUnit timer = { std::chrono::steady_clock::now() + timeout, timerCallback };
+  timers.push(timer);
+  conditionVariable.notify_one();
+}
+
+void DefaultTimer::ThreadFunc()
+{
+  while (!shouldThreadStop)
+  {
+    std::unique_lock<std::mutex> lock(mutex);
+    if (timers.empty())
+    {
+      conditionVariable.wait(lock, [this]()->bool
+      {
+        return shouldThreadStop || !timers.empty();
+      });
+    }
+    else
+    {
+      conditionVariable.wait_until(lock, timers.top().fireAt);
+    }
+    // execute all expired timers and remove them
+    while (!shouldThreadStop && !timers.empty() && timers.top().fireAt <= std::chrono::steady_clock::now())
+    {
+      auto callback = timers.top().callback;
+      timers.pop();
+      // allow to put new timers while this timer is being processed
+      lock.unlock();
+      try
+      {
+        callback();
+      }
+      catch (...)
+      {
+        // do nothing, but the thread will be alive.
+      }
+      lock.lock();
+    }
+  }
+}