What is double locking in thread?
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.
What is double locking mechanism?
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.
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 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.
What is volatile variable in Java?
Volatile keyword is used to modify the value of a variable by different threads. The volatile keyword does not cache the value of the variable and always read the variable from the main memory. The volatile keyword cannot be used with classes or methods.
How do I stop cloned singleton breaking?
Prevent Singleton Pattern From Cloning To overcome the above issue, we need to implement/override the clone() method and throw an exception CloneNotSupportedException from the clone method. If anyone tries to create a clone object of Singleton , it will throw an exception, as shown in the below code.
Is double-checked locking broken?
The “Double-Checked Locking is Broken” Declaration. Double-Checked Locking is widely cited and used as an efficient method for implementing lazy initialization in a multithreaded environment. Unfortunately, it will not work reliably in a platform independent way when implemented in Java, without additional synchronization.
Does double-checked locking work in Java without synchronization?
Double-Checked Locking is widely cited and used as an efficient method for implementing lazy initialization in a multithreaded environment. Unfortunately, it will not work reliably in a platform independent way when implemented in Java, without additional synchronization.
Does double-checked locking work with Symantec JIT?
Paul Jakubik found an example of a use of double-checked locking that did not work correctly. A slightly cleaned up version of that code is available here . When run on a system using the Symantec JIT, it doesn’t work. In particular, the Symantec JIT compiles
Is it possible to lock a helper without using volatile fields?
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.