Common questions

Is double-checked locking thread safe?

Is double-checked locking thread safe?

In multi-threaded environments, initialization is usually not thread safe, so locking is required to protect the critical section. Since only the first access requires locking, double-checked locking is used to avoid locking overhead of subsequent accesses.

What is double check in singleton?

In double-checked locking, code checks for an existing instance of Singleton class twice with and without locking to make sure that only one instance of singleton gets created.

Why you need double-checked locking of Singleton class?

The double checked pattern is used to avoid obtaining the lock every time the code is executed. If the call are not happening together then the first condition will fail and the code execution will not execute the locking thus saving resources.

Is double locking must to create thread safe Singleton class?

By the way, this is not the best way to create thread-safe Singleton, you can use Enum as Singleton, which provides inbuilt thread-safety during instance creation. Another way is to use a static holder pattern. That’s all about double checked locking of Singleton class in Java.

Why is double-checked locking bad?

Note that there is actually no classic “double-check” pattern, since without the above fixes the pattern cannot work. This is why the double-check pattern is considered evil, since you simply can’t implement it correctly without atomics and fences. Instead you’re left using just a mutex locked section like below.

Why double-checked locking is broken?

If Helper is an immutable object, such that all of the fields of Helper are final, then double-checked locking will work without having to use volatile fields.

How can singleton be broken?

Serialization is used to convert an object of byte stream and save in a file or send over a network. Suppose you serialize an object of a singleton class. Then if you de-serialize that object it will create a new instance and hence break the singleton pattern.

Why double checked locking is broken?

Is a singleton thread safe?

Is singleton thread safe? A singleton class itself is not thread safe. Multiple threads can access the singleton same time and create multiple objects, violating the singleton concept. The singleton may also return a reference to a partially initialized object.

Do or make a double check?

transitive verb. Definition of DOUBLE CHECK. : a careful checking to determine accuracy, condition, or progress especially of something already checked.

What is double lock in Java?

Double-checked locking is the practice of checking a lazy-initialized object’s state both before and after a synchronized block is entered to determine whether or not to initialize the object.

Can a singleton design pattern break with double checked locking?

Here is the case in which singleton design pattern will break with this approach : This will bring us to double checked locking pattern, where we will also add one more null check inside synchronized block as shown below.

How to make a singleton thread safe in C + +?

You can use the function std::call_once to register a callable which will be executed exactly once. The flag std::call_once in the following implementation guarantees that the singleton will be thread-safe initialized. Here are the numbers. Of course, the most obvious way is it protects the singleton with a lock.

When do you need to double check a singleton in Java?

This double check lock is only necessary if you are worried about many threads calling the singleton simultaneously, or the cost of obtaining a lock in general. Its purpose is to prevent unnecessary synchronization, thereby keeping your code fast in a multi-threaded environment.

Is the Meyers Singleton safe in C + + 11?

The beauty of the Meyers Singleton in C++11 is that it’s automatically thread-safe. That is guaranteed by the standard: Static variables with block scope. The Meyers Singleton is a static variable with block scope, so we are done. It’s still left to rewrite the program for four threads.

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