Multithreading and locking?

[Ether]

Originally Posted by Skinkworks

our team does't use any lock/semaphore-type structures, and we've never had a problem

Zera's Law: Once you realize that something bad can happen, it will.

[bob.wolff68]

One example worth looking at is the PIDController. It spawns a task which updates every 50ms from the PIDInput and writes its results to PIDWrite. That will serve as a good example. But if there's a lack of clarity as to what you're really trying to do, here's "it" in a nutshell. Since you have two tasks running at the same time, one must be careful to not wind up modifying something while it is being read by the other task. The lock basically says that the other task cannot get their lock until you unlock on the other one. One must also be careful to program in a manner where you always give up a lock that you've taken - or else the other thread will be forever waiting to gain the lock which you never give up.... and similarly, if you take a lock, you have to be careful to make sure you don't accidentally call a function which tries to take the lock a 2nd time which would result in the same deadlock situation.

bob

[rbmj]

Originally Posted by Ether

Zera's Law: Once you realize that something bad can happen, it will.

I can attest to that. As soon as I took a second look at our code I realized that we'd had static initialization order issues, and sure enough, a few days later it segfaulted...

The AxisCamera code also has some locking that you can look at. We also wrapped it a little in our code: https://github.com/rbmj/612-code/blo...ion_thread.cpp

[jacob9706]

Originally Posted by rbmj

I can attest to that. As soon as I took a second look at our code I realized that we'd had static initialization order issues, and sure enough, a few days later it segfaulted...

The AxisCamera code also has some locking that you can look at. We also wrapped it a little in our code: https://github.com/rbmj/612-code/blo...ion_thread.cpp

I was looking through your code and do you realize you can use namespaces?

so for example right after your includes you would put something like this...

using namespace cv;
using namespace std;


Now that you have that instead of doing something like

std::cout << cv:oint(10,10) << std::endl;

You can now do this

cout << Point(10,10) << endl;

Just something I thought I would share with everyone.

[knuckleduster]

Originally Posted by jacob9706

I was looking through your code and do you realize you can use namespaces?

so for example right after your includes you would put something like this...

using namespace cv;
using namespace std;

Just something I thought I would share with everyone.

Actually, it isn't really considered good practice to use namespaces, when you start using multiple libraries with similarly named functions, it can get hectic, and its just better to get into the habit of not using them if possible.