What is double check locking in Singleton?

What is double check locking 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.

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 you need double-checked locking of Singleton class?

then both synchronize. and then, they check again, and still see it null. and create two different objects. OOOPS.

What is a double lock and why it is used?

In software engineering, double-checked locking (also known as “double-checked locking optimization”) is a software design pattern used to reduce the overhead of acquiring a lock by testing the locking criterion (the “lock hint”) before acquiring the lock.

Is double checked?

To double-check means to review something twice, to be sure that no mistakes have been made. When accuracy is extremely important, one may be asked to triple-check data. However, triple-check is not currently a word recognized by the Oxford English Dictionary.

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 locking padlock?

Click to enlarge] Most padlocks will open if you cut the shackle. However, if it is double locked then even if you cut it, then both sides of the shackle remain in place. On top of that, if it is locked down using a ball bearing, it means that even if cut, the shackle can’t rotate (See image on the right).

Why volatile is used in Singleton?

The volatile prevents memory writes from being re-ordered, making it impossible for other threads to read uninitialized fields of your singleton through the singleton’s pointer.

Can you double confirm?

If you’re using the word “confirm” to verify something, just use the word “confirm”. To add “double” before “confirm” is unnecessary because “confirm” already implies something is definite.

Is Double check or double check?

Double-check is a hyphenated compound word, which is a term composed of two words joined together by a hyphen. Related words are double-checks, double-checked, double-checking. Note that double-check is correctly rendered with a hyphen, though the term is also seen as two separate words, as in double check.

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.

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