Hi all, I have a query about multithreading. What I would like to do is, at the start of my main update() function, start a couple of threads in parallel, once they are all complete carry on with my main update function.
I am having trouble getting this working the way I want. I don't want my threads to loop continuously independent of my main update loop, I want them all to start at the beginning of my update loop, and then once they are all finished, feed the data around, then render, then repeat.
I tried creating a thread every update loop which runs only once (no while() in the function) - it works and behaves fine for a few minutes, then the threads just stop being created - no crash or hang, just no updates from threads. I also tried using an infinte while() but with a flag that determined whether the code ran that frame or not, and only set that flag at the beginning of the main update loop (code for this below) - that one is very stable, but behaviour was weird, I think the thread updates weren't being called when I wanted them to.
I've read a lot of documentation on multithreading in general and all the pthread commands. I understand the fundamentals of protecting data and all that.. but I'm just lacking a lot of experience and strategy .. so any suggestions welcome!
This is my thread class I'm using which has the infinite loop in the threaded function, but only runs the update function if the flag is set. I initialize the flag at the beginning of each main update with thread1->runOnce(); thread2->runOnce(); etc.... but it doesn't run smoothly.
controlling the behavior ( which we are interested ) with a variable which is certainly not in context for the segments of the program, in such a case there is no need for the threads to branch out ( obey ) execution based on the value of the boolean variables
another thing that I could smell is, the possibility of mutual lock ( am guessing it ) where it just runs fine for a instant ' t ' units of time after that gets into the mutual lock condition.
Is the behavior of working fine for few minutes and receiving no updates a constant behavior ? I mean is it happening at 'nth' instant of time each time? If so, my assumption might be wrong - else there is a possibility
One more question, ( sorry if its silly ) do you check/validate the creation of threads ? Since its running in an infinite loop, conditions might go wrong and outbursting with the maximum number of threads that can be created.
One more question, ( sorry if its silly ) do you check/validate the creation of threads ? Since its running in an infinite loop, conditions might go wrong and outbursting with the maximum number of threads that can be created.
I think something like that was happening when I went down the 'create a new thread every loop' approach, which is why I scrapped that idea and went for the 'infinite loop in the thread, but only run the update function when the variable is set' approach.
I think I've actually identified the problem. I think it was the sleep() function in my thread loop. I understand why I need that if the loop is continuously running and doing heavy stuff, but do I need it in my case?
When I comment out the sleep line (As below), the behaviour looks a lot smoother and correct, maybe because as soon as I set the bHasRunThisFrame flag in the thread instance to false, the update function is called almost immediately (which is what I want), whereas with the sleep() function, maybe there was a delay of upto interval before the update kicked in?.... or something :P Is it bad to not have a sleep function in there?
I've been out of the game for a while with C++ but as I read your post, I was reminded of some classes I wrote to manage multiple threads. Also, Bartosz Milewski of Reliable Software - Creators of the distributed version control system, Code Co-op wrote a really cool critical section class wrapper that totally protects against accidentally leaving a lock in place. His discussion of how resource management is the key to reliable message driven software was well done and he had numerous ways to protect against leaving resources open or laying around that would cause memory leaks or hangs. Here it is:
I take this question of the The Linux Programming Interface: A Linux and Unix System Programming page 652 exercise 30.1
I want someone to explain the under line statement because it sounds complex to me couldn't understand anything
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