Check usage of Semaphores

[MichaelRoeder]

Description

Using Semaphores becomes an issue if "permits" are lost, e.g., if an exception is thrown between acquiring and releasing a permit.

semaphore.acquire();
// do something that causes an exception
semaphore.release();

To this end, it should look like the following:

semaphore.acquire();
try {
    // do something that causes an exception
} finally {
    semaphore.release();
}

It should be noted that the try block does not need a catch block, i.e., it is not necessary to handle the exception at this place. The important point is that releasing the permit is done within the finally block and will be executed whenever the program leaves the try block.

Task

We should go through all usages of Semaphores in GERBIL to ensure that all of them are used like described above. This is necessary to avoid issues like #348.