atomicity

What do you mean by Atomic instructions? How does the following become Atomic? TestAndSet int TestAndSet(int *x){ register int temp = *x; *x = 1; return temp; } From a software perspective, if one does not want to use non-blocking synchronization primitives, how can one ensure Atomicity of instruction? is it possible only at Hardware or some assembly level directive optimization can be used? Some machine instructions are intrinsically atomic - for example, reading and writing properly aligned values of the native processor word size is atomic on many architectures . This means that hardware

I've actually heard claims both ways. I suspect they are not, but I wanted to get the topic settled. C++03 does not know about the existance of threads, therefore the concept of atomicity doesn't make much sense for C++03, meaning that it doesn't say anything about that. C++11 does know about threads, but once again doesn't say anything about the atomicity of assigning pointers. However C++11 does contain std::atomic<T*> , which is guaranteed to be atomic. Note that even if writing to a raw pointer is atomic on your platform the compiler is still free to move that assingment around, so that

I'm running on a 32-bit machine and I'm able to confirm that long values can tear using the following code snippet which hits very quickly. static void TestTearingLong() { System.Threading.Thread A = new System.Threading.Thread(ThreadA); A.Start(); System.Threading.Thread B = new System.Threading.Thread(ThreadB); B.Start(); } static ulong s_x; static void ThreadA() { int i = 0; while (true) { s_x = (i & 1) == 0 ? 0x0L : 0xaaaabbbbccccddddL; i++; } } static void ThreadB() { while (true) { ulong x = s_x; Debug.Assert(x == 0x0L || x == 0xaaaabbbbccccddddL); } } But when I try something similar

I'm building a real-time poll in Firebase. Each vote is stored in a list field. To prevent having to pull every vote down to the client in order to count them, I cache the tallies for each choice in counter fields. poll1 counts choice1: 5 choice2: 2 choice3: 10 choice4: 252 voters uid1 : choice1 uid6 : choice3 uid25: choice2 uid31: choice1 I'm currently updating the counter with the following transaction: var fireCountPush = new Firebase(self.fireCountUrl+node+id); fireCountPush.transaction(function(current_value) { return current_value + 1; }, function(error, committed, snapshot) { if

Recently I was reading a tutorial, in that I came across a statement that says.. "The Java language specification guarantees that reading or writing a variable is an atomic operation(unless the variable is of type long or double ). Operations variables of type long or double are only atomic if they declared with the volatile keyword." AtomicInteger or AtomicLong that provides methods like getAndDecrement() , getAndIncrement() and getAndSet() which are atomic. I got confused a bit with the above statement.. could you please clarify when to use AtomicInteger or AtomicLong classes. JB Nizet Doing

In most of the discussions I've read, it indicates that making a property atomic does not guarantee it to be thread-safe, it just guarantees that the value returned won't be garbage as a result of one object writing to it and another trying to read it at the same time. I understand this isn't thread-safe as a third object could be writing it and while the object accessing it wouldn't get garbage back, it's not entirely certain which value it will get back as multiple objects are writing to it at the same time, and it may get any of their values. So when we say it won't return garbage, would

I am trying to create a view where I save an object but I'd like to undo that save if some exception is raised. This is what I tried: class MyView(View): @transation.atomic def post(self, request, *args, **kwargs): try: some_object = SomeModel(...) some_object.save() if something: raise exception.NotAcceptable() # When the workflow comes into this condition, I think the previous save should be undome # Whant am I missing? except exception.NotAcceptable, e: # do something What am I doing wrong? even when the exception is raised some_object is still in DataBase. Atomicity Documentation To