concurrentmodification

问题 I found this question in a textbook I am reading. The solution is given below it as well. I'm having trouble understanding how the minimum could be 2. Why couldn't a thread read 0, all other threads execute and it writes 1? And whether it is 1 or 2, the thread writing last must still complete its own loop? int n = 0; int main(int argc, char **argv) { for (i = 0; i < 5; i++) { int tmp = n; tmp = tmp + 1; n = tmp; } return 0; } If a single thread ran this application, you would expect the final

问题 This question already has answers here : Why is a ConcurrentModificationException thrown and how to debug it (7 answers) Closed 9 months ago . I was reading this "Freuqent Java concurrency problems" question and got confused by an answer talking about java.util.ConcurrentModificationException. My understanding of the answer is that this can occur in a single-threaded program. How or what conditions cause the following code to throw the exception? List<String> list = new ArrayList<String>

问题 I'd like to run tests that simulate users modifying certain data at the same time for a grails application. Are there any plug-ins / tools / mechanisms I can use to do this efficiently? They don't have to be grails specific. It should be possible to fire multiple actions in parallel. I'd prefer to run the tests on functional level (so far I'm using Selenium for other tests) to see the results from the user perspective. Of course this can be done in addition to integration testing if you'd

问题 This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center. Closed 7 years ago . I'm creating a multithread chat in java. When user u1 sends a message to user u2 but user u2 is not connected, user u1 sends the message to the server

问题 I have the following code running, but I sometimes get some sort of concurrency exception when running it. ArrayList<Mob> carriers = new ArrayList<Mob>(); ArrayList<Mob> mobs = new ArrayList<Mob>(); ... for (Mob carrier : carriers){ for (Mob mob : mobs){ checkInfections (carrier, mob); } } I refactored it to solve the concurrency problem, but it did lead me to a question. Would there be a difference in performance if I change the for construct to an Iterator pattern? What's the access level

问题 I have the following code running, but I sometimes get some sort of concurrency exception when running it. ArrayList<Mob> carriers = new ArrayList<Mob>(); ArrayList<Mob> mobs = new ArrayList<Mob>(); ... for (Mob carrier : carriers){ for (Mob mob : mobs){ checkInfections (carrier, mob); } } I refactored it to solve the concurrency problem, but it did lead me to a question. Would there be a difference in performance if I change the for construct to an Iterator pattern? What's the access level

问题 With the snippet below I am, attempting to process a spreadsheet, with the twist of needing to exclude ad hoc columns. I know the crude way I am doing it, put the exceptions in an ArrayList and process the list on each and ever increment over the current row columns is perverse, but you know just get it done. However I am getting the titled error, which I believe should never happen. I am just looping through the ArrayList and comparing, not modifying anything. Where is the error? Is there a

问题 final Multimap<Term, BooleanClause> terms = getTerms(bq); for (Term t : terms.keySet()) { Collection<BooleanClause> C = new HashSet(terms.get(t)); if (!C.isEmpty()) { for (Iterator<BooleanClause> it = C.iterator(); it.hasNext();) { BooleanClause c = it.next(); if(c.isSomething()) C.remove(c); } } } Not a SSCCE, but can you pick up the smell? 回答1: The Iterator for the HashSet class is a fail-fast iterator. From the documentation of the HashSet class: The iterators returned by this class's

问题 I have a Server class and a Timer inside it which is supposed to clear dead clients (clients who crashed). I followed the example below by locking the collection when the Timer iterates over the users but I still get this exception (after I crash a connected client). http://www.javaperformancetuning.com/articles/fastfail2.shtml List<User> users; List<User> connectedUsers; ConcurrentMap<User, IClient> clients; ... users = Collections.synchronizedList(new ArrayList<User>()); connectedUsers =

问题 Exception in thread "main" java.util.ConcurrentModificationException Squash the PC dirties the room Violet. The room's state is now dirty Lily the animal growls The Animal Lily left the room and goes to Green through the west door. at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793) at java.util.HashMap$KeyIterator.next(HashMap.java:828) at homework5.Room.critReactRoomStateChange(Room.java:76) at homework5.PC.play(PC.java:121) at homework5.Main.main(Main.java:41) Java Result: 1 That