![]() ![]() Interval-Based Memory Reclamation, Haosen Wen et al., Proceedings of the 23rd ACM SIGPLAN Symposium on Principles and Practice of Parallel Programming (PPoPP), 2018. McKenney et al., Ottawa Linux Symposium, 2002. ![]() Hart et al., Journal of Parallel and Distributed Computing, 2007. Performance of Memory Reclamation for Lockless Synchronization, Thomas E. Michael, IEEE Transactions on Parallel and Distributed Systems, 2004. Hazard Pointers: Safe Memory Reclamation for Lock-Free Objects, Maged M. This is a general problem in non-blocking data structures and we generally don't consider it as the bug of the data structure itself-after all it only occurs in languages using manual memory management like C/C++ but not in those like Java (BTW, Michael & Scott Queue has been adopted in Java Concurrency for years). The paper of Interval-Based Memory Reclamation has much background discussed. You can take a look at these papers referred below for more details. As far as I know, epoch-based reclamations are widely adopted to handle this problem. They avoid use-after-free by reserving epochs and are faster than Hazard Pointers. There're also many epoch-based reclamation variants such as RCU, and most recently, interval-based reclamation (IBR). However, this mechanism incurs nontrivial performance overhead. before getting the data from the Queue, the subscribe function first executes lock.acquire(), then gets the data with data. Hazard Pointers allow the thread to reserve blocks so that other threads won't really reclaim them before it finishes. The first publisher Process publishes data to the Queue, the second subscriber Process reads the data from the Queue and logs. This is actually the non-blocking memory reclamation problem that’s being explored years since Maged Michael, one of the authors of MS queue, introduced Hazard Pointers. Thread 1 continues and advanced to D4, trying to read head.ptr->next, but as head.ptr is already freed by Thread 1, crash happens.Īnd my C++ code really always crashes at D4 for Thread 1.Ĭan anyone please point out my mistake and give some explanation ?.Thread 2 luckily advanced all the way to D20, at D19 it freed head.ptr.Thread 2 advanced to D3, read the same head as Thread 1.Otherwise, another dequeue might free the next nodeĭ19: free(head.ptr) // It is safe now to free the old nodeĭ20: return TRUE // Queue was not empty, dequeue succeeded Simple, Fast, and Practical Non-Blocking and BlockingĪnd the original Dequeue pseudo-code is as following: dequeue(Q: pointer to queue_t, pvalue: pointer to data type): booleanĭ1: loop // Keep trying until Dequeue is doneĭ4: next = head.ptr->next // Read Head.ptr->nextĭ5: if head = Q->Head // Are head, tail, and next consistent?ĭ6: if head.ptr = tail.ptr // Is queue empty or Tail falling behind?ĭ7: if next.ptr = NULL // Is queue empty?ĭ8: return FALSE // Queue is empty, couldn't dequeue To reverse it, type in the code again.I am studying Michael & Scott's lock-free queue algorithm and trying to implemented it in C++.īut I produced a race in my code and think there may be a race in the algorithm. ![]() But, if you collect any other health, it will be back to the normal 100 health. When in this prompt, type "give health 999" and you will get 999 health. Go to the console where you type all of the other cheats. "map levelname" in the console (that little thing when u press Level Skip To jump to any level you want, just type Go backwards 5 or 6 paces and run all the way to the waterfall and then jump when you are about to jump of the ledge and land inside the waterfall. In the Receiving center go to the area where you see a waterfall. Then look by the photos and step on all theīuttons and a hole will appear at the end of gallary. At the end of the short passage it says "Welcome to the id gallery". Shoot the crack in the wall and and follow the little passage way. Look straight at the button, turn around and you will see a few ammo packs and a little crack in the wall. There are two of them which are on either side of the play area. After you kill The final boss in the last level, seach around the play area were you fought the boss until you see a button on the ground. It will say "You have found a secret level"Ģ. It correctly you will see two bodies and a elevator. It will tell you "you have found a secret", and if you did Enter it and follow until you are in a sort of room of water, hold space bar until you see a little room. Next search around the bottom of the poolĪrea until you see a small tunnel. Now go inside the pool area and when you see the large crack on the bottom of the pool area go in to it by ducking because you are too tall to enter it if you are not ducking. Next grab the Rebreather and press B to activate it. Kill the two Light guards, then kill the Enforcer. In the first unit go to level 3, and walk forward until you see an Enforcer, a Rebreather and a large pool area. ![]()
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