feat: enhance race condition tests to verify producer resilience after consumer crash

Reviewed-on: #8

CMakeLists.txt

@@ -25,6 +25,15 @@ add_library(core
 target_include_directories(core PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include)
 target_link_libraries(core PUBLIC Qt5::Core)
 
+# Main Application
+add_executable(app
+    src/app/main.cxx
+    src/app/MainWindow.cxx
+    include/MainWindow.hpp
+)
+target_include_directories(app PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include)
+target_link_libraries(app PRIVATE core Qt5::Widgets)
+
 #tests
 enable_testing()
 add_subdirectory(tests)

docs/self-assessment.md

@@ -0,0 +1,25 @@
+# Self-Assessment
+
+## Two Real Difficulties
+
+**1. Maintaining TDD discipline under time pressure**
+
+Sticking to a strict test-first workflow throughout the session was genuinely hard. Between the deadline and the accumulated fatigue of a full day of work beforehand, there were moments where the temptation to just write the implementation and then fill the tests was real. I did not always resist it. Some tests were written after the fact rather than before, which is something I am aware of and want to be honest about.
+
+**2. Designing testable seams at the IPC and sysfs boundaries**
+
+The components that most needed testing were also the ones most coupled to external resources: a live socket and a real sysfs path. The difficulty was finding the right abstraction level, too thin and the tests require actual kernel resources; too thick and you end up testing your mocks, not your logic. The solution was to inject the transport as a plain `std::function` callback into the producer, and to point the sysfs reader at a controlled fake file on disk. Both approaches keep the core logic testable with no sockets, no threads, and no Qt, but arriving at that boundary (deciding what to abstract and what to leave concrete) required more iteration than I anticipated.
+
+---
+
+## Alternative IPC Mechanism Considered
+
+I evaluated POSIX shared memory with semaphores as an alternative to UNIX domain sockets. The theoretical appeal is clear: no serialization, no kernel-mediated data copy, potentially lower latency. However, I am considerably less practiced with `shm_open`/`mmap`/`sem_post` than I am with socket-based communication, and more importantly, shared memory is significantly harder to unit-test in isolation. Sockets expose a clean, file-descriptor-based interface that maps naturally to mock-able abstractions. Shared memory regions and semaphore lifecycles would have added complexity to the test harness for uncertain gain at this data rate. Domain sockets were the pragmatic choice.
+
+---
+
+## Design Decision Changed Mid-Development
+
+Initially I had planned a looser boundary between the core logic and Qt, with the producer potentially depending on Qt primitives for threading or signalling. Early on, I decided to keep Qt strictly confined to the GUI layer and the consumer thread, nothing more. The producer, the sysfs reader, and the IPC bridge are plain C++ with no Qt dependency whatsoever.
+
+The reason is simple: that code could be portable. If tomorrow the producer needs to run on a microcontroller, a bare-metal embedded target, or any environment where Qt is not available or not desirable, the only thing that needs replacing is the transport callback. The core logic moves untouched. It also makes unit-testing the producer significantly cleaner and easier, no Qt test infrastructure needed, just standard C++.

include/MainWindow.hpp

@@ -0,0 +1,32 @@
+#pragma once
+// MainWindow.hpp
+// SPDX-License-Identifier: GPL-3.0-only
+// Author: Unai Blazquez <unaibg2000@gmail.com>
+
+#include <QLabel>
+#include <QString>
+#include <QVBoxLayout>
+#include <QWidget>
+
+/// @brief Minimal GUI window that displays the last integer received
+///        from the ConsumerThread. Never blocks — values arrive via
+///        Qt's queued signal/slot mechanism.
+class MainWindow : public QWidget
+{
+  Q_OBJECT
+
+ public:
+  explicit MainWindow(QWidget* parent = nullptr);
+
+  /// @brief Returns the current text shown in the value label (for testing).
+  QString lastDisplayedText() const;
+
+ public slots:
+  /// @brief Slot connected to ConsumerThread::valueReceived.
+  ///        Updates the label with the new value.
+  void onValueReceived(int value);
+
+ private:
+  QLabel* m_title_label;
+  QLabel* m_value_label;
+};

src/app/MainWindow.cxx

@@ -0,0 +1,33 @@
+// MainWindow.cxx
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Author: Unai Blazquez <unaibg2000@gmail.com>
+
+#include "MainWindow.hpp"
+
+MainWindow::MainWindow(QWidget* parent) : QWidget(parent)
+{
+  setWindowTitle("Azkoyen IPC Monitor");
+  setMinimumSize(320, 120);
+
+  auto* layout = new QVBoxLayout(this);
+
+  m_title_label = new QLabel("Last received value:", this);
+  m_value_label = new QLabel("(waiting...)", this);
+
+  // Make the value label stand out a bit
+  QFont font = m_value_label->font();
+  font.setPointSize(24);
+  font.setBold(true);
+  m_value_label->setFont(font);
+  m_value_label->setAlignment(Qt::AlignCenter);
+
+  layout->addWidget(m_title_label);
+  layout->addWidget(m_value_label);
+}
+
+QString MainWindow::lastDisplayedText() const { return m_value_label->text(); }
+
+void MainWindow::onValueReceived(int value)
+{
+  m_value_label->setText(QString::number(value));
+}

src/app/main.cxx

@@ -0,0 +1,58 @@
+// main.cxx
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Author: Unai Blazquez <unaibg2000@gmail.com>
+
+#include <QApplication>
+#include <cstdlib>
+#include <fstream>
+#include <iostream>
+
+#include "Consumer.hpp"
+#include "MainWindow.hpp"
+#include "Producer.hpp"
+#include "UnixIpcBridge.hpp"
+
+int main(int argc, char* argv[])
+{
+  QApplication app(argc, argv);
+
+  const std::string socket_path = "/tmp/azkoyen.sock";
+  const std::string sysfs_path = "./fake_sysfs_input";
+
+  // 1. Consumer — listens on the socket, emits Qt signal on receive
+  ConsumerThread consumer(socket_path);
+
+  // 2. GUI — minimal window that displays received values
+  MainWindow window;
+  window.show();
+
+  // Connect consumer signal → window slot (auto-queued across threads,
+  // so the GUI never blocks even if the producer is stuck in cool-down)
+  QObject::connect(&consumer, &ConsumerThread::valueReceived, &window,
+                   &MainWindow::onValueReceived);
+
+  consumer.start();
+
+  // 3. Bridge — sends ints over the UNIX domain socket
+  UnixIpcBridge bridge(socket_path);
+
+  // 4. Producer — reads sysfs, generates random int, sends via bridge.
+  //    Logs to a file instead of console (console is for the consumer).
+  std::ofstream log_file("producer.log", std::ios::app);
+
+  Producer producer(
+      sysfs_path, [&bridge](int value) { bridge.send(value); },
+      []() { return std::rand() % 1000; },
+      [&log_file](const std::string& msg) { log_file << msg << std::endl; });
+
+  producer.start();
+
+  // 5. Run the Qt event loop (GUI stays responsive, signals are delivered)
+  int result = app.exec();
+
+  // 6. Graceful shutdown
+  producer.stop();
+  consumer.stop();
+
+  return result;
+}

tests/CMakeLists.txt

@@ -53,3 +53,38 @@ target_link_libraries(test_consumer
 )
 
 add_test(NAME test_consumer COMMAND test_consumer)
+
+add_executable(test_main_window
+    test_main_window.cxx
+    ${CMAKE_SOURCE_DIR}/src/app/MainWindow.cxx
+    ${CMAKE_SOURCE_DIR}/include/MainWindow.hpp
+)
+
+target_include_directories(test_main_window PRIVATE ${CMAKE_SOURCE_DIR}/include)
+
+target_link_libraries(test_main_window
+    PRIVATE
+        core
+        gtest
+        gtest_main
+        Qt5::Core
+        Qt5::Widgets
+        Qt5::Test
+)
+
+add_test(NAME test_main_window COMMAND test_main_window)
+
+add_executable(test_race_conditions
+    test_race_conditions.cxx
+)
+
+target_link_libraries(test_race_conditions
+    PRIVATE
+        core
+        gtest
+        gtest_main
+        Qt5::Core
+        Qt5::Test
+)
+
+add_test(NAME test_race_conditions COMMAND test_race_conditions)

tests/test_consumer.cxx

@@ -1,7 +1,11 @@
 #include <gtest/gtest.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
 
 #include <QCoreApplication>
 #include <QSignalSpy>
+#include <cstring>
 
 #include "Consumer.hpp"
 #include "UnixIpcBridge.hpp"
@@ -118,3 +122,94 @@ TEST(ConsumerThreadTest, StopsCleanlyWhenNeverStarted)
   // stop() on a consumer that was never started must not crash
   consumer.stop();
 }
+
+// ---------------------------------------------------------------------------
+// Requirement 2: Consumer receiving corrupted data (non-numeric)
+// ---------------------------------------------------------------------------
+
+/// Helper: raw-connect to a UNIX socket and send arbitrary bytes.
+static void send_raw_bytes(const std::string& path, const void* data,
+                           size_t len)
+{
+  int fd = socket(AF_UNIX, SOCK_STREAM, 0);
+  ASSERT_GE(fd, 0);
+
+  struct sockaddr_un addr = {};
+  addr.sun_family = AF_UNIX;
+  std::strncpy(addr.sun_path, path.c_str(), sizeof(addr.sun_path) - 1);
+
+  ASSERT_EQ(
+      connect(fd, reinterpret_cast<sockaddr*>(&addr), sizeof(addr)), 0);
+
+  if (len > 0)
+  {
+    ::send(fd, data, len, 0);
+  }
+  close(fd);
+}
+
+TEST(ConsumerThreadTest, DropsCorruptedShortMessage)
+{
+  const std::string sock = "/tmp/test_ct_corrupt_short.sock";
+
+  ConsumerThread consumer(sock);
+  QSignalSpy spy(&consumer, &ConsumerThread::valueReceived);
+  consumer.start();
+
+  // Send only 2 bytes instead of sizeof(int)==4 — corrupted / partial message
+  uint16_t garbage = 0xBEEF;
+  send_raw_bytes(sock, &garbage, sizeof(garbage));
+
+  // Give the consumer time to process (or not)
+  spy.wait(500);
+  consumer.stop();
+
+  // No signal should have been emitted
+  EXPECT_EQ(spy.count(), 0);
+}
+
+TEST(ConsumerThreadTest, DropsEmptyConnection)
+{
+  const std::string sock = "/tmp/test_ct_corrupt_empty.sock";
+
+  ConsumerThread consumer(sock);
+  QSignalSpy spy(&consumer, &ConsumerThread::valueReceived);
+  consumer.start();
+
+  // Connect and immediately close — zero bytes sent
+  send_raw_bytes(sock, nullptr, 0);
+
+  spy.wait(500);
+  consumer.stop();
+
+  EXPECT_EQ(spy.count(), 0);
+}
+
+TEST(ConsumerThreadTest, SurvivesCorruptedThenReceivesValid)
+{
+  const std::string sock = "/tmp/test_ct_corrupt_then_valid.sock";
+
+  ConsumerThread consumer(sock);
+  QSignalSpy spy(&consumer, &ConsumerThread::valueReceived);
+  consumer.start();
+
+  // First: send corrupted (1 byte)
+  uint8_t one_byte = 0xFF;
+  send_raw_bytes(sock, &one_byte, sizeof(one_byte));
+  std::this_thread::sleep_for(std::chrono::milliseconds(50));
+
+  // Then: send a valid int via the normal bridge
+  UnixIpcBridge bridge(sock);
+  bridge.send(777);
+
+  // Wait for the valid signal
+  for (int attempt = 0; spy.count() < 1 && attempt < 20; ++attempt)
+  {
+    spy.wait(100);
+  }
+  consumer.stop();
+
+  // The corrupted message must have been dropped, valid one received
+  ASSERT_EQ(spy.count(), 1);
+  EXPECT_EQ(spy.at(0).at(0).toInt(), 777);
+}

tests/test_main_window.cxx

@@ -0,0 +1,47 @@
+#include <gtest/gtest.h>
+
+#include <QApplication>
+#include <QLabel>
+#include <QSignalSpy>
+#include <cstdlib>
+
+#include "MainWindow.hpp"
+
+// QWidget-based tests need a full QApplication (not QCoreApplication).
+// Use offscreen platform so tests run headless in containers.
+static int argc_ = 0;
+static char* argv_[] = {nullptr};
+static struct SetupOffscreen
+{
+  SetupOffscreen() { qputenv("QT_QPA_PLATFORM", "offscreen"); }
+} setup_offscreen_;
+static QApplication app_(argc_, argv_);
+
+TEST(MainWindowTest, LabelUpdatesOnValueReceived)
+{
+  MainWindow window;
+  // Simulate receiving a value from ConsumerThread
+  window.onValueReceived(42);
+
+  // The label should display the received value
+  EXPECT_NE(window.lastDisplayedText().toStdString().find("42"),
+            std::string::npos);
+}
+
+TEST(MainWindowTest, LabelUpdatesMultipleTimes)
+{
+  MainWindow window;
+  window.onValueReceived(10);
+  window.onValueReceived(20);
+  window.onValueReceived(30);
+
+  // Label should show the most recent value
+  EXPECT_NE(window.lastDisplayedText().toStdString().find("30"),
+            std::string::npos);
+}
+
+TEST(MainWindowTest, WindowTitleIsSet)
+{
+  MainWindow window;
+  EXPECT_FALSE(window.windowTitle().isEmpty());
+}

tests/test_race_conditions.cxx

@@ -0,0 +1,177 @@
+// test_race_conditions.cxx
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Author: Unai Blazquez <unaibg2000@gmail.com>
+
+#include <gtest/gtest.h>
+
+#include <QCoreApplication>
+#include <QSignalSpy>
+#include <atomic>
+#include <chrono>
+#include <fstream>
+#include <iostream>
+#include <stdexcept>
+#include <thread>
+#include <vector>
+
+#include "Consumer.hpp"
+#include "Producer.hpp"
+#include "UnixIpcBridge.hpp"
+
+static int argc_ = 0;
+static QCoreApplication app_(argc_, nullptr);
+
+
+TEST(RaceConditionTest, RepeatedStartStopWhileProducerSends)
+{
+  const std::string sock = "/tmp/test_race.sock";
+  constexpr int kCycles = 20;
+
+  // Watchdog: if the test takes longer than 15s, declare deadlock.
+  std::atomic<bool> test_done{false};
+  std::thread watchdog([&test_done]() {
+    for (int i = 0; i < 150 && !test_done.load(); ++i)
+    {
+      std::this_thread::sleep_for(std::chrono::milliseconds(100));
+    }
+    if (!test_done.load())
+    {
+      std::cerr
+          << "DEADLOCK DETECTED: RepeatedStartStopWhileProducerSends timed out"
+          << std::endl;
+      std::abort();
+    }
+  });
+
+  std::atomic<bool> producer_running{true};
+  std::thread producer([&]() {
+    while (producer_running.load())
+    {
+      try
+      {
+        UnixIpcBridge bridge(sock);
+        bridge.send(42);
+      }
+      catch (const std::runtime_error&)
+      {
+        // Expected: consumer socket not ready or just torn down.
+      }
+      std::this_thread::sleep_for(std::chrono::milliseconds(5));
+    }
+  });
+
+  for (int i = 0; i < kCycles; ++i)
+  {
+    ConsumerThread consumer(sock);
+    consumer.start();
+
+    // Let it run briefly so the producer can connect during some cycles.
+    std::this_thread::sleep_for(std::chrono::milliseconds(10 + (i % 5) * 5));
+
+    // stop() must return without deadlock every single time.
+    consumer.stop();
+  }
+
+  producer_running.store(false);
+  producer.join();
+
+  test_done.store(true);
+  watchdog.join();
+
+  // If we reach here, no deadlock across kCycles start/stop cycles.
+  SUCCEED();
+}
+
+TEST(RaceConditionTest, ProducerSurvivesConsumerCrash)
+{
+  const std::string sock = "/tmp/test_crash.sock";
+  const std::string sysfs = "./fake_sysfs_race";
+
+  // Prepare sysfs file so the producer is in Enabled state.
+  { std::ofstream(sysfs) << "1\n"; }
+
+  // Track what the producer sends.
+  std::vector<int> sent_values;
+  std::mutex sent_mutex;
+  std::vector<std::string> logs;
+  std::mutex log_mutex;
+
+  auto make_safe_send = [&](const std::string& path) {
+    return [&, path](int value) {
+      try
+      {
+        UnixIpcBridge bridge(path);
+        bridge.send(value);
+        std::lock_guard<std::mutex> lk(sent_mutex);
+        sent_values.push_back(value);
+      }
+      catch (const std::runtime_error&)
+      {
+        // Consumer is down — expected during the "crash" window.
+      }
+    };
+  };
+
+  Producer producer(
+      sysfs, make_safe_send(sock), []() { return 123; },
+      [&](const std::string& msg) {
+        std::lock_guard<std::mutex> lk(log_mutex);
+        logs.push_back(msg);
+      },
+      [](std::chrono::milliseconds) {
+        // Use a short sleep so the test runs fast.
+        std::this_thread::sleep_for(std::chrono::milliseconds(20));
+      });
+
+  // Phase 1: start consumer, start producer, let a few values flow.
+  {
+    ConsumerThread consumer(sock);
+    QSignalSpy spy(&consumer, &ConsumerThread::valueReceived);
+    consumer.start();
+    producer.start();
+
+    // Wait for at least 2 values to arrive.
+    for (int attempt = 0; spy.count() < 2 && attempt < 50; ++attempt)
+    {
+      spy.wait(100);
+    }
+    ASSERT_GE(spy.count(), 2) << "Phase 1: producer should have delivered values";
+
+    // "Crash" the consumer: stop + destroy.
+    consumer.stop();
+  }
+
+  // Phase 2: producer is still running with no consumer (sends will fail).
+  std::this_thread::sleep_for(std::chrono::milliseconds(200));
+
+  // Phase 3: bring up a fresh consumer. Producer should resume delivering.
+  {
+    ConsumerThread consumer2(sock);
+    QSignalSpy spy2(&consumer2, &ConsumerThread::valueReceived);
+    consumer2.start();
+
+    for (int attempt = 0; spy2.count() < 2 && attempt < 50; ++attempt)
+    {
+      spy2.wait(100);
+    }
+
+    consumer2.stop();
+
+    ASSERT_GE(spy2.count(), 2)
+        << "Phase 3: producer must deliver to a new consumer after crash";
+
+    // Values received by the second consumer should all be 123.
+    for (int i = 0; i < spy2.count(); ++i)
+    {
+      EXPECT_EQ(spy2.at(i).at(0).toInt(), 123);
+    }
+  }
+
+  producer.stop();
+
+  // Producer logged throughout all three phases.
+  {
+    std::lock_guard<std::mutex> lk(log_mutex);
+    EXPECT_GE(logs.size(), 3u) << "Producer should have kept logging";
+  }
+}