1. nested threads in C++
Situation
I was writing a unit test for my GlobalThreadManager Singleton Class:
TEST_F(ThreadManagerTest, ThreadIdGeneration) {
std::vector<std::thread> jobs;
std::atomic<int> completion_counter{ 0 };
// Given: 10 threads are generated asynchronously by 10 different threads using GlobalThreadManager, total 100 threads
for (int i = 0; i < 10; i++) {
jobs.push_back(std::thread([this, &completion_counter]() {
for (int j = 0; j < 10; j++) {
GlobalThreadManager->Launch([this, &completion_counter]() {
std::lock_guard<std::mutex> lock(thread_id_mutex);
thread_ids.insert(CurrentThreadId);
completion_counter++;
});
}
}));
}
for (auto& job : jobs) {
if (job.joinable()) {
job.join();
}
}
// job is registered by join, but not guaranteed to complete.
// need to wait until all jobs are done.
while (completion_counter < 100) {
std::this_thread::sleep_for(std::chrono::milliseconds(10));
}
// Then: Number of threads in the GlobalThreadManager thread pool should be 100, and they must all have unique ids.
ASSERT_EQ(GlobalThreadManager->GetThreadPool().size(), 100);
ASSERT_EQ(thread_ids.size(), 100);
}
After running the test, I figured out that all the assert stations pass, but the test itself terminates with error code 3.
Reason For Bug
- By waiting until completion_counter = 100, we guarantee that the 100 threads “Launch"ed by GlobalThreadManager has incremented their completion counter.
- However, this does not guarantee that All the threads “terminated” - it just means that all 100 threads executed its final statement and is ready to terminate.
- The join() statement guarantees that the 10 subthreads in the “jobs” vector terminated, but it doesn’t guarantee the termination of its 10 subthreads.
Fix
Add GlobalThreadManager.Join() at the end of the test to guarantee all threads are terminated before Destructor is called.
TEST_F(ThreadManagerTest, ThreadIdGeneration) {
std::vector<std::thread> jobs;
std::atomic<int> completion_counter{ 0 };
// Given: 10 threads are generated asynchronously by 10 different threads using GlobalThreadManager, total 100 threads
for (int i = 0; i < 10; i++) {
jobs.push_back(std::thread([this, &completion_counter]() {
for (int j = 0; j < 10; j++) {
GlobalThreadManager->Launch([this, &completion_counter]() {
std::lock_guard<std::mutex> lock(thread_id_mutex);
thread_ids.insert(CurrentThreadId);
completion_counter++;
});
}
}));
}
for (auto& job : jobs) {
if (job.joinable()) {
job.join();
}
}
// job is registered by join, but not guaranteed to complete.
// need to wait until all jobs are done.
while (completion_counter < 100) {
std::this_thread::sleep_for(std::chrono::milliseconds(10));
}
// Then: Number of threads in the GlobalThreadManager thread pool should be 100, and they must all have unique ids.
ASSERT_EQ(GlobalThreadManager->GetThreadPool().size(), 100);
ASSERT_EQ(thread_ids.size(), 100);
// add join!!!
GlobalThreadManager->Join();
}
2. Unreal Engine Build Error
Error 1
The "GenerateMSBuildEditorConfig" task failed unexpectedly.
System.UnauthorizedAccessException: Access to the path 'E:\UE_5.5\Engine\Source\Programs\AutomationTool\Mutable\RunMutableCommandlet\obj\Development\RunMutableCommandlet.Automation.GeneratedMSBuildEditorConfig.editorconfig' is denied.
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
at System.IO.StreamWriter.CreateFile(String path, Boolean append, Boolean checkHost)
at System.IO.StreamWriter..ctor(String path, Boolean append, Encoding encoding, Int32 bufferSize, Boolean checkHost)
at System.IO.File.InternalWriteAllText(String path, String contents, Encoding encoding, Boolean checkHost)
at Microsoft.CodeAnalysis.BuildTasks.GenerateMSBuildEditorConfig.WriteMSBuildEditorConfig()
at Microsoft.Build.BackEnd.TaskExecutionHost.Execute()
at Microsoft.Build.BackEnd.TaskBuilder.<ExecuteInstantiatedTask>d__26.MoveNext()
Error 2
Solution for Error 1
- Had to add write permission for user to
E:\UE_5.5
- Had to disable
read-onlyoption for the same directory as well
