chore: use condition variable to shutdown websocket pools (#5721)

CHANGELOG.md

@@ -131,6 +131,7 @@
 - Dev: Unified parsing of historic and live IRC messages. (#5678)
 - Dev: 7TV's `entitlement.reset` is now explicitly ignored. (#5685)
 - Dev: Qt 6.8 and later now default to the GDI fontengine. (#5710)
+- Dev: Moved to condition variables when shutting down worker threads. (#5721)
 
 ## 2.5.1
 

src/CMakeLists.txt

@@ -514,6 +514,8 @@ set(SOURCE_FILES
         util/LayoutHelper.hpp
         util/LoadPixmap.cpp
         util/LoadPixmap.hpp
+        util/OnceFlag.cpp
+        util/OnceFlag.hpp
         util/RapidjsonHelpers.cpp
         util/RapidjsonHelpers.hpp
         util/RatelimitBucket.cpp

src/providers/liveupdates/BasicPubSubManager.hpp

@@ -8,10 +8,12 @@
 #include "providers/twitch/PubSubHelpers.hpp"
 #include "util/DebugCount.hpp"
 #include "util/ExponentialBackoff.hpp"
+#include "util/OnceFlag.hpp"
 #include "util/RenameThread.hpp"
 
 #include <pajlada/signals/signal.hpp>
 #include <QJsonObject>
+#include <QScopeGuard>
 #include <QString>
 #include <QStringBuilder>
 #include <websocketpp/client.hpp>
@@ -120,6 +122,11 @@ public:
         this->work_ = std::make_shared<boost::asio::io_service::work>(
             this->websocketClient_.get_io_service());
         this->mainThread_.reset(new std::thread([this] {
+            // make sure we set in any case, even exceptions
+            auto guard = qScopeGuard([&] {
+                this->stoppedFlag_.set();
+            });
+
             runThread();
         }));
 
@@ -142,22 +149,34 @@ public:
 
         this->work_.reset();
 
-        if (this->mainThread_->joinable())
+        if (!this->mainThread_->joinable())
         {
-            // NOTE: We spawn a new thread to join the websocket thread.
+            return;
+        }
+
+        // NOTE:
         // There is a case where a new client was initiated but not added to the clients list.
         // We just don't join the thread & let the operating system nuke the thread if joining fails
         // within 1s.
-            auto joiner = std::async(std::launch::async, &std::thread::join,
+        if (this->stoppedFlag_.waitFor(std::chrono::seconds{1}))
-                                     this->mainThread_.get());
-            if (joiner.wait_for(std::chrono::seconds(1)) ==
-                std::future_status::timeout)
         {
+            this->mainThread_->join();
+            return;
+        }
+
         qCWarning(chatterinoLiveupdates)
-                    << "Thread didn't join within 1 second, rip it out";
+            << "Thread didn't finish within 1 second, force-stop the client";
         this->websocketClient_.stop();
+        if (this->stoppedFlag_.waitFor(std::chrono::milliseconds{100}))
+        {
+            this->mainThread_->join();
+            return;
         }
-        }
+
+        qCWarning(chatterinoLiveupdates)
+            << "Thread didn't finish after stopping, discard it";
+        // detach the thread so the destructor doesn't attempt any joining
+        this->mainThread_->detach();
     }
 
 protected:
@@ -394,6 +413,7 @@ private:
 
     liveupdates::WebsocketClient websocketClient_;
     std::unique_ptr<std::thread> mainThread_;
+    OnceFlag stoppedFlag_;
 
     const QString host_;
 

src/providers/twitch/PubSubManager.cpp

@@ -15,10 +15,10 @@
 #include "util/RenameThread.hpp"
 
 #include <QJsonArray>
+#include <QScopeGuard>
 
 #include <algorithm>
 #include <exception>
-#include <future>
 #include <iostream>
 #include <memory>
 #include <thread>
@@ -560,6 +560,11 @@ void PubSub::start()
     this->work = std::make_shared<boost::asio::io_service::work>(
         this->websocketClient.get_io_service());
     this->thread = std::make_unique<std::thread>([this] {
+        // make sure we set in any case, even exceptions
+        auto guard = qScopeGuard([&] {
+            this->stoppedFlag_.set();
+        });
+
         runThread();
     });
     renameThread(*this->thread, "PubSub");
@@ -578,23 +583,36 @@ void PubSub::stop()
 
     this->work.reset();
 
-    if (this->thread->joinable())
+    if (!this->thread->joinable())
     {
-        // NOTE: We spawn a new thread to join the websocket thread.
+        return;
+    }
+
+    // NOTE:
     // There is a case where a new client was initiated but not added to the clients list.
     // We just don't join the thread & let the operating system nuke the thread if joining fails
     // within 1s.
     // We could fix the underlying bug, but this is easier & we realistically won't use this exact code
     // for super much longer.
-        auto joiner = std::async(std::launch::async, &std::thread::join,
+    if (this->stoppedFlag_.waitFor(std::chrono::seconds{1}))
-                                 this->thread.get());
-        if (joiner.wait_for(1s) == std::future_status::timeout)
     {
-            qCWarning(chatterinoPubSub)
+        this->thread->join();
-                << "Thread didn't join within 1 second, rip it out";
+        return;
+    }
+
+    qCWarning(chatterinoLiveupdates)
+        << "Thread didn't finish within 1 second, force-stop the client";
     this->websocketClient.stop();
+    if (this->stoppedFlag_.waitFor(std::chrono::milliseconds{100}))
+    {
+        this->thread->join();
+        return;
     }
-    }
+
+    qCWarning(chatterinoLiveupdates)
+        << "Thread didn't finish after stopping, discard it";
+    // detach the thread so the destructor doesn't attempt any joining
+    this->thread->detach();
 }
 
 bool PubSub::listenToWhispers()

src/providers/twitch/PubSubManager.hpp

@@ -3,6 +3,7 @@
 #include "providers/twitch/PubSubClientOptions.hpp"
 #include "providers/twitch/PubSubWebsocket.hpp"
 #include "util/ExponentialBackoff.hpp"
+#include "util/OnceFlag.hpp"
 
 #include <boost/asio/io_service.hpp>
 #include <boost/asio/ssl/context.hpp>
@@ -267,6 +268,8 @@ private:
     const QString host_;
     const PubSubClientOptions clientOptions_;
 
+    OnceFlag stoppedFlag_;
+
     bool stopping_{false};
 
 #ifdef FRIEND_TEST

src/util/OnceFlag.cpp

@@ -0,0 +1,33 @@
+#include "util/OnceFlag.hpp"
+
+namespace chatterino {
+
+OnceFlag::OnceFlag() = default;
+OnceFlag::~OnceFlag() = default;
+
+void OnceFlag::set()
+{
+    {
+        std::unique_lock guard(this->mutex);
+        this->flag = true;
+    }
+    this->condvar.notify_all();
+}
+
+bool OnceFlag::waitFor(std::chrono::milliseconds ms)
+{
+    std::unique_lock lock(this->mutex);
+    return this->condvar.wait_for(lock, ms, [this] {
+        return this->flag;
+    });
+}
+
+void OnceFlag::wait()
+{
+    std::unique_lock lock(this->mutex);
+    this->condvar.wait(lock, [this] {
+        return this->flag;
+    });
+}
+
+}  // namespace chatterino

src/util/OnceFlag.hpp

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <chrono>
+#include <condition_variable>
+#include <mutex>
+
+namespace chatterino {
+
+/// @brief A flag that can only be set once which notifies waiters.
+///
+/// This can be used to synchronize with other threads. Note that waiting
+/// threads will be suspended.
+class OnceFlag
+{
+public:
+    OnceFlag();
+    ~OnceFlag();
+
+    /// Set this flag and notify waiters
+    void set();
+
+    /// @brief Wait for at most `ms` until this flag is set.
+    ///
+    /// The calling thread will be suspended during the wait.
+    ///
+    /// @param ms The maximum time to wait for this flag
+    /// @returns `true` if this flag was set during the wait or before
+    bool waitFor(std::chrono::milliseconds ms);
+
+    /// @brief Wait until this flag is set by another thread
+    ///
+    /// The calling thread will be suspended during the wait.
+    void wait();
+
+private:
+    std::mutex mutex;
+    std::condition_variable condvar;
+    bool flag = false;
+};
+
+}  // namespace chatterino

tests/CMakeLists.txt

@@ -51,6 +51,7 @@ set(test_SOURCES
     ${CMAKE_CURRENT_LIST_DIR}/src/Plugins.cpp
     ${CMAKE_CURRENT_LIST_DIR}/src/TwitchIrc.cpp
     ${CMAKE_CURRENT_LIST_DIR}/src/IgnoreController.cpp
+    ${CMAKE_CURRENT_LIST_DIR}/src/OnceFlag.cpp
     ${CMAKE_CURRENT_LIST_DIR}/src/lib/Snapshot.cpp
     ${CMAKE_CURRENT_LIST_DIR}/src/lib/Snapshot.hpp
     # Add your new file above this line!

tests/src/OnceFlag.cpp

@@ -0,0 +1,88 @@
+#include "util/OnceFlag.hpp"
+
+#include "Test.hpp"
+
+#include <thread>
+
+using namespace chatterino;
+
+// this test shouldn't time out (no assert necessary)
+TEST(OnceFlag, basic)
+{
+    OnceFlag startedFlag;
+    OnceFlag startedAckFlag;
+    OnceFlag stoppedFlag;
+
+    std::thread t([&] {
+        startedFlag.set();
+        startedAckFlag.wait();
+        std::this_thread::sleep_for(std::chrono::milliseconds{50});
+        stoppedFlag.set();
+    });
+
+    startedFlag.wait();
+    startedAckFlag.set();
+    stoppedFlag.wait();
+
+    t.join();
+}
+
+TEST(OnceFlag, waitFor)
+{
+    OnceFlag startedFlag;
+    OnceFlag startedAckFlag;
+    OnceFlag stoppedFlag;
+
+    std::thread t([&] {
+        startedFlag.set();
+        startedAckFlag.wait();
+
+        std::this_thread::sleep_for(std::chrono::milliseconds{100});
+        stoppedFlag.set();
+    });
+
+    startedFlag.wait();
+    startedAckFlag.set();
+
+    auto start = std::chrono::system_clock::now();
+    ASSERT_TRUE(stoppedFlag.waitFor(std::chrono::milliseconds{200}));
+    auto stop = std::chrono::system_clock::now();
+
+    ASSERT_LT(stop - start, std::chrono::milliseconds{150});
+
+    start = std::chrono::system_clock::now();
+    ASSERT_TRUE(stoppedFlag.waitFor(std::chrono::milliseconds{1000}));
+    stop = std::chrono::system_clock::now();
+
+    ASSERT_LT(stop - start, std::chrono::milliseconds{10});
+
+    start = std::chrono::system_clock::now();
+    stoppedFlag.wait();
+    stop = std::chrono::system_clock::now();
+
+    ASSERT_LT(stop - start, std::chrono::milliseconds{10});
+
+    t.join();
+}
+
+TEST(OnceFlag, waitForTimeout)
+{
+    OnceFlag startedFlag;
+    OnceFlag startedAckFlag;
+    OnceFlag stoppedFlag;
+
+    std::thread t([&] {
+        startedFlag.set();
+        startedAckFlag.wait();
+        std::this_thread::sleep_for(std::chrono::milliseconds{100});
+        stoppedFlag.set();
+    });
+
+    startedFlag.wait();
+    startedAckFlag.set();
+
+    ASSERT_FALSE(stoppedFlag.waitFor(std::chrono::milliseconds{25}));
+    stoppedFlag.wait();
+
+    t.join();
+}