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Thread Safety

In EEROS, blocks are basically accessed by multiple threads. EEROS blocks feature thread safety by providing exclusive access to critical memory locations by a mutex.

Concurrency can not be tested by Google Test framework. Therefore, test executables are needed which can be executed manually or via bash scripts.

To provide an example, a test program testing the Gain block is described below. The full source code is available on GitHub at:

The problem

The following code snipped and image show the issue simulated in the test program. The main thread calls on the gain object. This method is doing a long calculation. Thread t2 is unfortunately changing the gain by calling g1.setGain(gM2) during the main threads calculation. This will finally lead to an unexpected result.

Matrix<M,N> gM1;
Matrix<M,N> gM2;

Gain<Matrix<M,N>, Matrix<M,N>,true> g1{gM1};
Constant<Matrix<M,N>> c1{m2};

std::thread t2{[&] {

Matrix<M,N> res = g1.getOut().getSignal().getValue();

// Note: The above code is simplified for a better understanding. 

The solution

The Gain block is now implemented thread safe by using the class lock_guard and a mutex. The code snipped below shows the setGain() method as an example.

virtual void setGain(Tgain c) {
  std::lock_guard<std::mutex> lock(mtx);
  gain = c;

The test program will not show an unexpected result anymore. To see the unexpected result, the locking mechanism must be removed (comment std::lock_guard<std::mutex> lock(mtx);).

for_developers/thread_safety.txt · Last modified: 2019/11/01 10:11 by kunz