concurrency

问题 what is the default concurrency control for SQL Server 2005? Is it optimistic concurrency control or pessimistic concurrency control? Can this be set? Thanks in anticipation 回答1: "Pessimistic" seems to be the default in 2005, although snapshot isolation can be activated if desired: In the default pessimistic model, the first writer will block all subsequent writers, but using SI, subsequent writers could actually receive error messages and the application would need to resubmit the original

问题 I am look into the book "Java Concurrency in Practice" and found really hard to believe below quoted statement (But unfortunately it make sense). http://www.informit.com/store/java-concurrency-in-practice-9780321349606 Just wanted to get clear about this 100% public class Holder { private int n; public Holder(int n) { this.n = n; } public void assertSanity() { if (n != n) throw new AssertionError("This statement is false."); } } While it may seem that field values set in a constructor are the

问题 While experimenting with HashMap , I noticed something weird. Ran 4 threads with each trying to put (key,value) with keys from 0 to 9999, value a constant string. After all threads were done, map.size() returned a value greater than 10,000. How did this happen? Does this mean that the map contains duplicate keys? I iterated on the map.entrySet() and found that the count for some keys were indeed more than 1. What value would be returned if I do a get() on the map for one such key. Here is the

问题 I would like to define a do_in_parallel function in python that will take in functions with arguments, make a thread for each and perform them in parallel. The function should work as so: do_in_parallel(_sleep(3), _sleep(8), _sleep(3)) I am however having a hard time defining the do_in_parallel function to take multiple functions with multiple arguments each, here's my attempt: from time import sleep import threading def do_in_parallel(*kwargs): tasks = [] for func in kwargs.keys(): t =

问题 I want to implement an Anytime k-NN classifier but I cannot find a way to call the "classify(...)" method for a specific amount of time, suspend it, get the available results before the method was suspended, resume the method for a specific amount of time, suspend it, get the available results before the method was suspended, and so on... I use a data structure for getting approximate results. While the algorithm traverses the data structure, it will encounter the actual training data vector,

问题 I have an interesting issue which I am not sure what the root cause is. I have a server and two virtual hosts A and B with ports running on 80 and 81 respectively. I have written a simple PHP code on A which looks like this: <?php echo "from A server\n"; And another simple PHP code on B: <?php echo "B server:\n"; // create curl resource $ch = curl_init(); // set url curl_setopt($ch, CURLOPT_URL, "localhost:81/a.php"); //return the transfer as a string curl_setopt($ch, CURLOPT_RETURNTRANSFER,

问题 I have multiple processes running on different machines which are required to read/write to a shared XML file, for this I am using DOM with Java and FileLocks (While I know that a database would be a more effective approach, this is not viable due to project constraints) . To make changes to the XML file, the relevant process first creates an exclusively locked channel which is used to read the file, it then attempts to reuse the same channel to write the new version before closing the

问题 This question already has answers here : Strange code in java.util.concurrent.LinkedBlockingQueue (4 answers) Closed last year . I'm a little confused by the structure of the Node class in OpenJDK's implementation of LinkedBlockingQueue (in java.util.concurrent). I've reproduced the description of the node class below: static class Node<E> { E item; /** * One of: * - the real successor Node * - this Node, meaning the successor is head.next * - null, meaning there is no successor (this is the

问题 I was wondering what the best way to do concurrent HTTP requests in PHP? I have a lot of data to get and i'd rather do multiple requests at once to retrieve it all. Does anybody know how I can do this? Preferably in an anonymous/callback function mannor... Thanks, Tom. 回答1: You can use curl_multi, which internally fires off multiple separate requests under a single curl handle. But otherwise PHP itself not in any way/shape/form "multithreaded" and will not allow things to run in parallel,

问题 I am currently working on a Java application (Benchmark) that has for purpose to mesure some processes relative to a database. My application is supposed to run has following : I have several Usecases (simple insert, simple update, etc., in a database) that I would like to run multiple times. The only difference between the runs, would be the number of threads running at the same time. I need to bench these usecases using 1, 2, 4, 8, 16, etc.. threads in order to include concurrency in my