That’s pretty easy: class Sample { private String message = null; private final Object lock = new Object(); public void newMessage(String x) { synchronized (lock) { message = x; } } public String getMessage() { synchronized (lock) { String temp = message; message = null; return temp; } } } Note that I didn’t either … Read more
semaphores have a synchronized counter and mutex’s are just binary (true / false). A semaphore is often used as a definitive mechanism for answering how many elements of a resource are in use — e.g., an object that represents n worker threads might use a semaphore to count how many worker threads are available. Truth … Read more
One thing to note is that the instant you receive such information, it’s stale. In other words, you could be told that no-one has the lock, but then when you try to acquire it, you block because another thread took out the lock between the check and you trying to acquire it. Brian is right … Read more
Since this question was first posted, an Android app has been added to the market that can checkout Git repos, called Agit. It can’t commit or push yet, but the clone/fetch/pull functionality is useful. The other issue is that a patched version of ConnectBot needs to be installed before Agit if you want to use … Read more
Collections.synchronizedMap() guarantees that each atomic operation you want to run on the map will be synchronized. Running two (or more) operations on the map however, must be synchronized in a block. So yes – you are synchronizing correctly.
Boy, what a question. The answer to which is: Yes, no, hmmm, well, it depends It all comes down to the architecture of the system. On an IA32 a correctly aligned address will be an atomic operation. Unaligned writes might be atomic, it depends on the caching system in use. If the memory lies within … Read more
The JVM is allowed to assume that other threads do not change the pizzaArrived variable during the loop. In other words, it can hoist the pizzaArrived == false test outside the loop, optimizing this: while (pizzaArrived == false) {} into this: if (pizzaArrived == false) while (true) {} which is an infinite loop. To ensure … Read more
The accepted answer is no good. The question describes an issue with synced folders, not shared folders. The proposed solution would have no effect on an rsynced (not shared) folder. And even if the OP was using a shared folder, the accepted answer’s suggestion is something that had already been integrated into vagrant as of … Read more
Using deferreds like Futures. var sequence = Futures.sequence(); sequence .then(function(next) { http.get({}, next); }) .then(function(next, res) { res.on(“data”, next); }) .then(function(next, d) { http.get({}, next); }) .then(function(next, res) { … }) If you need to pass scope along then just do something like this .then(function(next, d) { http.get({}, function(res) { next(res, d); }); }) .then(function(next, … Read more
It’s not a matter of better, just different. When you synchronize a method, you are effectively synchronizing to the object itself. In the case of a static method, you’re synchronizing to the class of the object. So the following two pieces of code execute the same way: public synchronized int getCount() { // … } … Read more