race-condition

One of the answers to the question of what race conditions are mentioned low-level algorithms deliberately using race condition. How can race conditions be beneficial? EDIT: Concurrency and queues are a good example of deliberately not caring about ordering of things, as long as nothing is lost. Any ideas on how "really hairy low-level algorithms do this on purpose" ? Not all races are equally bad. The worst kind of race that you can get is reading of partial results. This is what Herb Sutter referred to as 'seeing pink elephants': your program is able to observe an intermediate state that

Suppose our code has 2 threads (A and B) have a reference to the same instance of this class somewhere: public class MyValueHolder { private int value = 1; // ... getter and setter } When Thread A does myValueHolder.setValue(7) , there is no guarantee that Thread B will ever read that value: myValueHolder.getValue() could - in theory - keep returning 1 forever. In practice however, the hardware will clear the second level cache sooner or later, so Thread B will read 7 sooner or later (usually sooner). Is there any way to make the JVM emulate that worst case scenario for which it keeps

I am writing a hotel booking software using PHP and MySQL. I am pretty much done with it but I ran into a race condition problem. For example there is only one standard room left and when 2 guests both select it it shows available to both of them. I tried fixing it by checking the room again when the guest clicks confirm before payment but that still has issues. I also tried making the room status to pending when whoever clicks the confirm first but I can't figure out how to change it back to available if the guest decides not to pay or just closes the browser. I searched SO for answers but I

This manpage for the dup2 system call says: EBUSY (Linux only) This may be returned by dup2() or dup3() during a race condition with open(2) and dup(). What race condition does it talk about and what should I do if dup2 gives EBUSY error? Should I retry like in the case of EINTR ? There is an explanation in fs/file.c , do_dup2() : /* * We need to detect attempts to do dup2() over allocated but still * not finished descriptor. NB: OpenBSD avoids that at the price of * extra work in their equivalent of fget() - they insert struct * file immediately after grabbing descriptor, mark it larval if *

The hello world demo for Flask is: from flask import Flask app = Flask(__name__) @app.route("/") def hello(): return "Hello World!" if __name__ == "__main__": app.run() What if I modified this like so: from flask import Flask app = Flask(__name__) a = 1 b = 2 c = 3 @app.route("/") def hello(): a += 1 b += a c += b return "Hello World!" if __name__ == "__main__": app.run() I understand WSGI application might have multiple threads. The hello function could be running on multiple threads at the same time, and then we'd have a race condition. Is this correct? If the above code is not thread safe,

I've been reading other questions on how to implement if-exists-insert-else-update semantics in EF, but either I'm not understanding how the answers work, or they are in fact not addressing the issue. A common solution offered is to wrap the work in a transaction scope (eg: Implementing if-not-exists-insert using Entity Framework without race conditions ): using (var scope = new TransactionScope()) // default isolation level is serializable using(var context = new MyEntities()) { var user = context.Users.SingleOrDefault(u => u.Id == userId); // * if (user != null) { // update the user user

Here's the scenario: My users are presented a grid, basically, a stripped down version of a spreadsheet. There are textboxes in each row in the grid. When they change a value in a textbox, I'm performing validation on their input, updating the collection that's driving the grid, and redrawing the subtotals on the page. This is all handled by the OnChange event of each textbox. When they click the "Save" button, I'm using the button's OnClick event to perform some final validation on the amounts, and then send their entire input to a web service, saving it. At least, that's what happens if they

I know that compound operations such as i++ are not thread safe as they involve multiple operations. But is checking the reference with itself a thread safe operation? a != a //is this thread-safe I tried to program this and use multiple threads but it didn't fail. I guess I could not simulate race on my machine. EDIT: public class TestThreadSafety { private Object a = new Object(); public static void main(String[] args) { final TestThreadSafety instance = new TestThreadSafety(); Thread testingReferenceThread = new Thread(new Runnable() { @Override public void run() { long countOfIterations =