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Implementing Read-Write Locks with Double-Checked Locking


Implementing Read-Write Locks with Double-Checked Locking

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Implementing Read-Write Locks with Double-Checked Locking
Tag : java , By : algoRhythm99
Date : November 28 2020, 01:01 AM


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(invalid way to) avoid double checked locks in C#


Tag : chash , By : simonth
Date : March 29 2020, 07:55 AM
wish helps you No, because thread switch can happen right after two threads pass if (!IsInitialized)
There is a great article where this topic is explained in context of creating singleton: http://csharpindepth.com/Articles/General/Singleton.aspx (by Jon Skeet)

Can I avoid the volatile read in double checked locking once initialized like this?


Tag : java , By : Hitesh Prajapati
Date : March 29 2020, 07:55 AM
hope this fix your issue No, you cannot. If thread A has reached the synchronized block and is executing the
instance = new Singleton();

Memory read visibility ordering vs write order using double-checked locking


Tag : chash , By : user150694
Date : March 29 2020, 07:55 AM
will help you No, because inited is not volatile. volatile gives you the memory release and acquire fences you need in order to establish the correct happens-before relationship.
If there's no release fence before inited is set to true, then the value may not be completely written by the time another thread reads inited and sees it as true, which could result in a half-constructed object being returned. Similarly, if there's a release fence but no corresponding acquire fence before reading inited in the first check, it's possible that the object is fully constructed, but that the CPU core that saw inited as true hasn't yet seen the memory effects of value being written (cache coherency does not necessarily mandate that the effects of consecutive writes are seen in order on other cores). This would again potentially result in a half-constructed object being returned.
private class Memoized<T>
{
    public T value;
    public volatile bool inited;
}

private static Func<T> Memoize<T>(Func<T> func)
{
    var memoized = new Memoized<T>();

    return () => {
        if (memoized.inited)
            return memoized.value;

        lock (memoized) {
            if (!memoized.inited) {
                memoized.value = func();
                memoized.inited = true;
            }
        }

        return memoized.value;
    };
}

Convert double check locking from using synchronized to locks in JAVA


Tag : java , By : shehan
Date : March 29 2020, 07:55 AM
I hope this helps you . Transformation of synchronized blocks to the equivalent block using ReentrantLock is pretty rote.
First you create a lock with the same or similar scope and lifetime as the object you were locking on. Here you are locking on MyClass.class, hence a static lock, so you can map this to a static lock in MyClass, such as MyClass.initLock.
synchronized (object) {
lock.lock();
try {
} finally {
  lock.unlock();
}
private final static ReentrantLock initLock = new ReentrantLock();

private static void redoHeavyInitialisation() {
    if (needToReinitialise()) {
        MyClass.initLock.lock();
        try {
            if (needToReinitialise()) {
                doHeavyInitialisation();
            }
        } finally {
          MyClass.initLock.unlock();
        }
    }
}

What is the right way to write double-checked locking in Rust?


Tag : development , By : lietkynes
Date : March 29 2020, 07:55 AM
I wish did fix the issue.
Does Atomic_.store(true, Ordering::Release) affect other non-atomic write operations?
atomic.set(4, Ordering::Relaxed);
other = 8;
println!("{}", atomic.get(Ordering::Relaxed));
// thread 1
one = 1;
atomic.set(true, Ordering::Release);
two = 2;

// thread 2
while !atomic.get(Ordering::Acquire) {}

println!("{} {}", one, two);
struct Lazy<T> {
    initialized: AtomicBool,
    lock: Mutex<()>,
    value: UnsafeCell<Option<T>>,
}

impl<T> Lazy<T> {
    pub fn get_or_create<'a, F>(&'a self, f: F) -> &'a T
    where
        F: FnOnce() -> T
    {
        if !self.initialized.load(Ordering::Acquire) { // (1)
            let _lock = self.lock.lock().unwrap();

            if !self.initialized.load(Ordering::Relaxed) { // (2)
                let value = unsafe { &mut *self.value.get() };
                *value = Some(f(value));
                self.initialized.store(true, Ordering::Release); // (3)
            }
        }

        unsafe { &*self.value.get() }.as_ref().unwrap()
    }
}
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