I've been reading the answer to a similar question, but I'm still a little confused... Abel had a great answer, but this is the part that I'm unsure about: ...declaring a variable volatile makes it volatile for every single access. It is impossible to force this behavior any other way, hence volatile cannot be replaced with Int...
Consider the following code: int main() { int i; volatile int* p = &i; ...
From what I've read from Herb Sutter and others you would think that volatile and concurrent programming were completely orthogonal concepts, at least as far as C/C++ are concerned. However, in GCC c++0x extension all of std::atomic's member functions have the volatile qualifier. The same is true in Anthony Williams's implementation of...
As demonstrated in this answer I recently posted, I seem to be confused about the utility (or lack thereof) of volatile in multi-threaded programming contexts. My understanding is this: any time a variable may be changed outside the flow of control of a piece of code accessing it, that variable should be declared to be volatile. Signal...
I know, it has been made quite clear in a couple of questions/answers before, that volatile is related to the visible state of the c++ memory model and not to multithreading. On the other hand, this article by Alexandrescu uses the volatile keyword not as a runtime feature but rather as a compile time check to force the compiler into fa...
If you try to cout a pointer to a volatile type, even a volatile char pointer where you would normally expect cout to print the string, you will instead simply get '1' (assuming the pointer is not null I think). I assume output stream operator<< is template specialized for volatile pointers, but my question is, why? What use case motivat...
This question is mostly academic. I ask out of curiosity, not because this poses an actual problem for me. Consider the following incorrect C program. #include <signal.h> #include <stdio.h> static int running = 1; void handler(int u) { running = 0; } int main() { signal(SIGTERM, handler); while (running) ; pr...
A compiler cannot eliminate or reorder reads/writes to a volatile-qualified variables. But what about the cases where other variables are present, which may or may not be volatile-qualified? Scenario 1 volatile int a; volatile int b; a = 1; b = 2; a = 3; b = 4; Can the compiler reorder first and the second, or third and the fourth ...
Previously I've written some very simple multithreaded code, and I've always been aware that at any time there could be a context switch right in the middle of what I'm doing, so I've always guarded access the shared variables through a CCriticalSection class that enters the critical section on construction and leaves it on destruction. ...
Hi all, Consider the following Java code: volatile boolean v1 = false; volatile boolean v2 = false; //Thread A v1 = true; if (v2) System.out.println("v2 was true"); //Thread B v2 = true; if (v1) System.out.println("v1 was true"); If there was a globally visible total order for volatile accesses then at least one println wou...
int* Register = 0x00FF0000; // Address of micro-seconds timer while(*Register != 0); Should I declare *Register as volatile while using armcc compiler and -O0 optimization ? In other words: Does -O0 optimization requires qualifying that sort of variables as volatile ? (which is probably required in -O2 optimization) ...
As i understand, if we declare a variable as volatile, then it will not be stored in the local cache. Whenever thread are updating the values, it is updated to the main memory. So, other threads can access the updated value. But in the following program both volatile and non-volatile variables are displaying same value. The volatile ...
Assume that we have the following code: class Program { static volatile bool flag1; static volatile bool flag2; static volatile int val; static void Main(string[] args) { for (int i = 0; i < 10000 * 10000; i++) { if (i % 500000 == 0) { Console.WriteLine("{0:#,0}",i); } ...
I'm making a game in java and in used BufferedImages to render content to the screen. I had performance issues on low end machines where the game is supposed to run, so I switched to VolatileImage which are normally faster. Except they actually slow the whole thing down. The images are created with GraphicsConfiguration.createCompatible...
I'm not quite sure if it's safe to spin on a volatile variable in user-mode threads, to implement a light-weight spin_lock, I looked at the tbb source code, tbb_machine.h:170, //! Spin WHILE the value of the variable is equal to a given value /** T and U should be comparable types. */ template<typename T, typename U> void spin_wait_whi...
Marking a variable as volatile in Java ensures that every thread sees the value that was last written to it instead of some stale value. I was wondering how this is actually achieved. Does the JVM emit special instructions that flush the CPU cashes or something? ...
import java.util.concurrent.CountDownLatch; import java.util.concurrent.atomic.AtomicInteger; public class Main implements Runnable { private final CountDownLatch cdl1 = new CountDownLatch(NUM_THREADS); private volatile int bar = 0; private AtomicInteger count = new AtomicInteger(0); private static final int NUM_THREADS = ...
So far I have the below which is taken from http://www.danielmoth.com/Blog/volatile-registrykey.aspx public static class RegistryHelper { public static RegistryKey CreateVolatileSubKey(RegistryKey rk, string subkey, RegistryKeyPermissionCheck permissionCheck) { var rk2 = rk.GetType(); const BindingFlags bfStati...
There's a bit of code which writes data to a MemoryStream object directly into it's data buffer by calling GetBuffer(). It also uses and updates the Position and SetLength() properties appropriately. This code works properly 99.9999% of the time. Literally. Only every so many 100,000's of iterations it will barf. The specific problem i...
Does the out variable in the MyThread class need to be declared volatile in this code or will the "volatility" of the stdout variable in the ThreadTest class carry over? import java.io.PrintStream; class MyThread implements Runnable { int id; PrintStream out; // should this be declared volatile? MyThread(int id, PrintStrea...