Could HippoMocks be used within concurrent testcases just like this:
synchronized startup phase
create mock
register expectations etc.
parallel testing phase
call methods on the mock
synchronized teardown phase
verify the mock
I did not find an explicit statement regarding this issue. Here and there it is mentioned, that mocking non-virtual methods would destroy the possibility for thread-safety (HippoMocks: is it possible to mock non-virtual methods?) or that thread-safety could be added quite easily (unfortunately without actually revealing how). GoogleMock answers this question very clearly (https://github.com/google/googletest/blob/master/googlemock/docs/CookBook.md#using-google-mock-and-threads), such an information would be helpful here, too.
No, HippoMocks is not designed to be thread safe.
However, if you follow some simple rules you should be able to use mocks in a multithreaded environment:
Do the setup sequentially in one thread and use one single MockRepository.
Using different mocks in different threads should be safe.
Using one mock in different threads is safe, when you use only OnCall() setups. Combine it with OnCall().Do() and you should be able do a lot of testing this way.
Don't use ExpectCall - it is not safe.
UPDATE: Okay, I did it. I wrote a small test for multithreading
class IMulti
{
public:
virtual void A() =0;
virtual int B(int a) = 0;
};
const int THREAD_ITERATIONS = 1000;
static DWORD WINAPI run_thread(LPVOID args)
{
IMulti* im = static_cast<IMulti*>(args);
for (int i=0; i<THREAD_ITERATIONS; i++)
{
im->A();
int result = im->B(22);
std::cout << "task says: " << i <<" result:" << result <<"\n";
}
std:: cout << "finished";
return 0;
}
TEST(check_HippoMocksCanMultiThreadedConcurrentReadingViaOnCall)
{
MockRepository mocks;
IMulti* im = mocks.Mock<IMulti>();
mocks.OnCall(im, IMulti::A);
mocks.OnCall(im, IMulti::B).Return(4711);
HANDLE handles[2];
handles[0] = CreateThread(NULL, 0, &run_thread, im, 0, NULL);
handles[1] = CreateThread(NULL, 0, &run_thread, im, 0, NULL);
WaitForMultipleObjects(2, handles, TRUE, INFINITE);
}
The result is, that it works fine.
Now I made it a little bit harder and replaced the second OnCall by the following:
for (int i = 0; i< THREAD_ITERATIONS*2; i++)
{
mocks.ExpectCall(im, IMulti::B).Return(i);
}
Here you will get crashes randomly (just play around with the THREAD_ITERATIONS counter). The reason is, that the matched expectations are somehow counted in the Mockrepository.
Doing the setup concurently crashes, as expected.
Related
I am attempting to design a system in which I'll have multiple threads. All these threads share a common variable (which is atomic) at a time and when each thread starts it increments that variable and before that thread ends it decrements that variable. I would like a thread to block if the current value of that variable is greater than a specific limit value. A simple psuedocode is this:
std::atomic<int> var;
int limit = 3; //limit value
void doWork() //This method is run as multiple thread simultaneously
{
if(var.load() < limit)
{
//block until this condition is met
}
//increment
var++;
//Do some work
.....
//Decrement before leaving
var--
}
Now two approaches come to my mind. The first approach is to sleep while var.load < limit but this looks sub-optimal. The second approach is to use conditional_variable. I am using that approach below but I believe I have two issues here
The first thread will block on cv.wait(lk, []{return var.load() <
limit});
Multiple threads wont be doing work only one will do work
while others will be blocked.
I would appreciate it if someone can suggest on how I can remove these defects from the code below or if there is a better approach ?
std::condition_variable cv;
std::mutex cv_m;
std::atomic<int> var;
int limit = 3; //limit value
void doWork()
{
std::unique_lock<std::mutex> lk(cv_m);
std::cerr << "Waiting... \n";
cv.wait(lk, []{
return var.load() < limit
});
//Increment var
var++;
//Do some Work
...
//Decrement Work
var--
cv.notify_all();
}
I'll preface this by saying that I'm delving into multithreading for the first time. Despite a lot of reading on concurrency and synchronization, I'm not readily seeing a solution for the requirements I've been given.
Using C++11 and Boost, I'm trying to figure out how to send data from a worker thread to a main thread. The worker thread is spawned at the start of the application and continuously monitors a lock free queue. Objects populate this queue at various intervals. This part is working.
Once the data is available, it needs to be processed by the main thread since another signal will be sent to the rest of the application which cannot be on a worker thread. This is what I'm having trouble with.
If I have to block the main thread through a mutex or a condition variable until the worker thread is done, how will that improve responsiveness? I might as well just stay with a single thread so I have access to the data. I must be missing something here.
I have posted a couple questions, thinking that Boost::Asio was the way to go. There is an example of how signals and data can be sent between threads, but as the responses indicate, things get quickly overly-complicated and it's not working perfectly:
How to connect signal to boost::asio::io_service when posting work on different thread?
Boost::Asio with Main/Workers threads - Can I start event loop before posting work?
After speaking with some colleagues, it was suggested that two queues be used -- one input, one output. This would be in shared space and the output queue would be populated by the worker thread. The worker thread is always going but there would need to be a Timer, probably at the application level, that would force the main thread to examine the output queue to see if there were any pending tasks.
Any ideas on where I should direct my attention? Are there any techniques or strategies that might work for what I'm trying to do? I'll be looking at Timers next.
Thanks.
Edit: This is production code for a plugin system that post-processes simulation results. We are using C++11 first wherever possible, followed by Boost. We are using Boost's lockfree::queue. The application is doing what we want on a single thread but now we are trying to optimize where we see that there are performance issues (in this case, a calculation happening through another library). The main thread has a lot of responsibilities, including database access, which is why I want to limit what the worker thread actually does.
Update: I have already been successful in using std::thread to launch a worker thread that examines a Boost lock::free queue and processes tasks placed it in. It's step 5 in #Pressacco's response that I'm having trouble with. Any examples returning a value to the main thread when a worker thread is finished and informing the main thread, rather than simply waiting for the worker to finish?
If your objective is develop the solution from scratch (using native threads, queues, etc.):
create a thread save queue queue (Mutex/CriticalSection around add/remove)
create a counting semaphore that is associated with the queue
have one or more worker threads wait on the counting semaphore (i.e. the thread will block)
the semaphore is more efficient than having the thread constantly poll the queue
as messages/jobs are added to the queue, increment the semaphore
a thread will wake up
the thread should remove one message
if a result needs to be returned...
setup another: Queue+Semaphore+WorkerThreads
ADDITIONAL NOTES
If you decide to implement a thread safe queue from scratch, take a look at:
Synchronization between threads using Critical Section
With that said, I would take another look at BOOST. I haven't used the library, but from what I hear it will most likely contain some relevant data structures (e.g. a thread safe queue).
My favorite quote from the MSDN:
"When you use multithreading of any sort, you potentially expose
yourself to very serious and complex bugs"
SIDEBAR
Since you are looking at concurrent programming for the first time, you may wish to consider:
Is your objective to build production worthy code , or is this simply a learning exercise?
production? consider us existing proven libraries
learning? consider writing the code from scratch
Consider using a thread pool with an asynchronous callback instead of native threads.
more threads != better
Are threads really needed?
Follow the KISS principle.
The feedback above led me in the right direction for what I needed. The solution was definitely simpler than having to use signals/slots or Boost::Asio as I had previously attempted. I have two lock-free queues, one for input (on a worker thread) and one for output (on the main thread, populated by the worker thread). I use a timer to schedule when the output queue is processed. The code is below; perhaps it is of use to somebody:
//Task.h
#include <iostream>
#include <thread>
class Task
{
public:
Task(bool shutdown = false) : _shutdown(shutdown) {};
virtual ~Task() {};
bool IsShutdownRequest() { return _shutdown; }
virtual int Execute() = 0;
private:
bool _shutdown;
};
class ShutdownTask : public Task
{
public:
ShutdownTask() : Task(true) {}
virtual int Execute() { return -1; }
};
class TimeSeriesTask : public Task
{
public:
TimeSeriesTask(int value) : _value(value) {};
virtual int Execute()
{
std::cout << "Calculating on thread " << std::this_thread::get_id() << std::endl;
return _value * 2;
}
private:
int _value;
};
// Main.cpp : Defines the entry point for the console application.
#include "stdafx.h"
#include "afxwin.h"
#include <boost/lockfree/spsc_queue.hpp>
#include "Task.h"
static UINT_PTR ProcessDataCheckTimerID = 0;
static const int ProcessDataCheckPeriodInMilliseconds = 100;
class Manager
{
public:
Manager()
{
//Worker Thread with application lifetime that processes a lock free queue
_workerThread = std::thread(&Manager::ProcessInputData, this);
};
virtual ~Manager()
{
_workerThread.join();
};
void QueueData(int x)
{
if (x > 0)
{
_inputQueue.push(std::make_shared<TimeSeriesTask>(x));
}
else
{
_inputQueue.push(std::make_shared<ShutdownTask>());
}
}
void ProcessOutputData()
{
//process output data on the Main Thread
_outputQueue.consume_one([&](int value)
{
if (value < 0)
{
PostQuitMessage(WM_QUIT);
}
else
{
int result = value - 1;
std::cout << "Final result is " << result << " on thread " << std::this_thread::get_id() << std::endl;
}
});
}
private:
void ProcessInputData()
{
bool shutdown = false;
//Worker Thread processes input data indefinitely
do
{
_inputQueue.consume_one([&](std::shared_ptr<Task> task)
{
std::cout << "Getting element from input queue on thread " << std::this_thread::get_id() << std::endl;
if (task->IsShutdownRequest()) { shutdown = true; }
int result = task->Execute();
_outputQueue.push(result);
});
} while (shutdown == false);
}
std::thread _workerThread;
boost::lockfree::spsc_queue<std::shared_ptr<Task>, boost::lockfree::capacity<1024>> _inputQueue;
boost::lockfree::spsc_queue<int, boost::lockfree::capacity<1024>> _outputQueue;
};
std::shared_ptr<Manager> g_pMgr;
//timer to force Main Thread to process Manager's output queue
void CALLBACK TimerCallback(HWND hWnd, UINT nMsg, UINT nIDEvent, DWORD dwTime)
{
if (nIDEvent == ProcessDataCheckTimerID)
{
KillTimer(NULL, ProcessDataCheckPeriodInMilliseconds);
ProcessDataCheckTimerID = 0;
//call function to process data
g_pMgr->ProcessOutputData();
//reset timer
ProcessDataCheckTimerID = SetTimer(NULL, ProcessDataCheckTimerID, ProcessDataCheckPeriodInMilliseconds, (TIMERPROC)&TimerCallback);
}
}
int main()
{
std::cout << "Main thread is " << std::this_thread::get_id() << std::endl;
g_pMgr = std::make_shared<Manager>();
ProcessDataCheckTimerID = SetTimer(NULL, ProcessDataCheckTimerID, ProcessDataCheckPeriodInMilliseconds, (TIMERPROC)&TimerCallback);
//queue up some dummy data
for (int i = 1; i <= 10; i++)
{
g_pMgr->QueueData(i);
}
//queue a shutdown request
g_pMgr->QueueData(-1);
//fake the application's message loop
MSG msg;
bool shutdown = false;
while (shutdown == false)
{
if (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
else
{
shutdown = true;
}
}
return 0;
}
Here is a simplified version of my situation:
void AppendToVector(std::vector<int>* my_vector) {
for (int i = 0; i < 100; i++) {
my_vector->push_back(i);
}
}
void CreateVectors(const int num_threads) {
std::vector<std::vector<int>* > my_vector_of_pointers(10);
ThreadPool pool(num_threads);
for (for int i = 0; i < 10; i++) {
my_vector_of_pointers[i] = new std::vector<int>();
pool.AddTask(AppendToVector,
&my_vector_of_pointers[i]);
}
}
My question is whether I need to put a mutex lock in AppendToVector when running this with multiple threads? My intuition tells me I do not have to because there is no possibility of two threads accessing the same data, but I am not fully confident.
Every thread is appending different std::vector (inside AppendToVector function) so there is no need for locking in your case. In case you change your code in the way more than one thread access same vector then you will need lock. Don't be confused because std::vectors you are passing to AppendToVector are them-selfs elements of main std::list, it matters only that here threads are manipulating with completely different (not shared) memory
I have a thread class with two functions:
using namespace System::Threading;
public ref class SecThr
{
public:
int j;
void wralot()
{
for (int i=0; i<=400000;i++)
{
j=i;
if ((i%10000)==0)
Console::WriteLine(j);
}
}
void setalot()
{
Monitor::Enter(this);
for (int i=0; i<=400000;i++)
{
j=7;
}
Monitor::Exit(this);
}
};
int main(array<System::String ^> ^args)
{
Console::WriteLine("Hello!");
SecThr^ thrcl=gcnew SecThr;
Thread^ o1=gcnew Thread(gcnew ThreadStart(thrcl, &SecThr::wralot));
Thread^ o2=gcnew Thread(gcnew ThreadStart(thrcl, &SecThr::setalot));
o2->Start();
o1->Start();
o1->Join();
o2->Join();
So, for locking "setalot" function i've used MOnitor::Enter-Exit block. But the output is like i'm running only one thread with function "wralot"
0
10000
20000
30000
40000
7 //here's "setalot" func
60000
e t.c.
Why all the output data is not changed to const (7) by "setalot" func
I think you've misunderstood what Monitor::Enter does. It's only a cooperative lock - and as wralot doesn't try to obtain the lock at all, the actions of setalot don't affect it. It's not really clear why you expected to get a constant output of 7 due to setalot - if wralot did try to obtain the lock, it would just mean that one of them would "win" and the other would have to wait. If wralot had to wait, there'd be no output while setalot was running, and then wralot would go do its thing - including setting j to i on every iteration.
So basically, both threads are starting, and setalot very quickly sets j to 7 a lot of times... that's likely to complete in the twinkling of an eye in computer terms, compared with a Console.WriteLine call. I suggest you add a call to Console::WriteLine at the end of setalot so you can see when it's finished. Obviously after that, it's completely irrelevant - which is why you're seeing 60000, 70000 etc.
I'm browsing source codes from two applications sharing one queue using MSMQ. The first application has a thread that writes into the queue while the second application has another thread that reads from the queue. Ordinarily, if you're implementing your own queue, the applications would need a mutex when accessing the queue, right? However, I could not find any mutex/critical section in the source codes of these applications. Did I just miss something? Or does MSMQ not need any mutex since it is handled internally, is there such thing?
The MSMQ documentation states that:
Only the following methods are thread
safe: BeginPeek, BeginReceive,
EndPeek(IAsyncResult),
EndReceive(IAsyncResult),
GetAllMessages, Peek, and Receive.
MSMQ.Send() is not inherently thread-safe.
Send is thread safe, as long as you
always send a Message object and never
use send a .NET object directly. Using
the Message object, BTW, is always a
good idea - since it lets you add
label, timeouts, recoverable option
and all this stuff that make your MSMQ
solution a real enterprise solution.
class Program
{
static MessageQueue outQueue;
static void Main(string[] args)
{
outQueue = new MessageQueue(#".\private$\mtQueue");
for (int i = 0; i < 100; i++)
{
Thread thr = new Thread(new ThreadStart(MyThreadProc));
thr.Start();
}
}
static void MyThreadProc()
{
Message msg = new Message();
for (int i = 0; i < 100; i++)
{
msg.Label = string.Format("{0} : {1}",
Thread.CurrentThread.ManagedThreadId,
i);
outQueue.Send(msg);
}
}
}
From: Is Send() thread safe?