Question: Which Data Structure Is Thread Safe?

What does it mean thread safe?

In the simplest of terms threadsafe means that it is safe to be accessed from multiple threads.

When you are using multiple threads in a program and they are each attempting to access a common data structure or location in memory several bad things can happen.

So, you add some extra code to prevent those bad things..

Which is better HashMap or Hashtable?

Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones. Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.

What do you mean by ArrayList is not synchronized?

1) Synchronization: ArrayList is non-synchronized which means multiple threads can work on ArrayList at the same time. For e.g. if one thread is performing an add operation on ArrayList, there can be an another thread performing remove operation on ArrayList at the same time in a multithreaded environment.

Which of the following options is thread safe?

2) Read-only or final variables in Java are also thread-safe in Java. 3) Locking is one way of achieving thread-safety in Java. 4) Static variables if not synchronized properly become a major cause of thread-safety issues. 5) Example of thread-safe class in Java: Vector, Hashtable, ConcurrentHashMap, String etc.

What makes a function thread safe?

A piece of code is thread-safe if it functions correctly during simultaneous execution by multiple threads. In particular, it must satisfy the need for multiple threads to access the same shared data, and the need for a shared piece of data to be accessed by only one thread at any given time.

Which is faster HashMap or ConcurrentHashMap?

If you choose a single thread access use HashMap , it is simply faster. For add method it is even as much as 3x more efficient. Only get is faster on ConcurrentHashMap , but not much. When operating on ConcurrentHashMap with many threads it is similarly effective to operating on separate HashMaps for each thread.

Which is better linked list or ArrayList?

LinkedList is implemented as a double linked list. Its performance on add and remove is better than Arraylist, but worse on get and set methods. Vector is similar with ArrayList, but it is synchronized. ArrayList is a better choice if your program is thread-safe.

How do you make an ArrayList thread safe?

Method 1: Using Collections.synchronizedList() method It is imperative that user manually synchronize on the returned list when iterating over it. A thread-safe variant of ArrayList in which all mutative operations (e.g. add, set, remove..) are implemented by creating a separate copy of underlying array.

What is thread safe and non thread safe?

Thread Safe (TS) and Non-Thread Safe (TS) are the two different PHP builds available. Thread-safety ensures that when the shared data structure is manipulated by different threads, it is free from race conditions. … Non-thread-safe version on the other hand is used where PHP is installed as a CGI binary.

Is write thread safe?

So the conclusion and answer to the question is that write() is completely thread safe and multiple calls to it are executed after each other.

Is HashMap thread safe?

HashMap is non synchronized. It is not-thread safe and can’t be shared between many threads without proper synchronization code whereas Hashtable is synchronized. It is thread-safe and can be shared with many threads.

Are singletons thread safe?

Thread Safe Singleton: A thread safe singleton in created so that singleton property is maintained even in multithreaded environment. To make a singleton class thread-safe, getInstance() method is made synchronized so that multiple threads can’t access it simultaneously.

How do you prove a HashMap is not thread safe?

You are very likely to get the exception that will mean the HashMap is not thread safe….If you are going to attempt to write a unit test that demonstrates incorrect behavior, I recommend the following:Create a bunch of keys that all have the same hashcode (say 30 or 40)Add values to the map for each key.More items…

Is ArrayList thread safe?

ArrayList , on the other hand, is unsynchronized, making them, therefore, not thread safe. With that difference in mind, using synchronization will incur a performance hit. So if you don’t need a thread-safe collection, use the ArrayList .

What is not thread safe?

Conditionally safe: Different threads can access different objects simultaneously, and access to shared data is protected from race conditions. Not thread safe: Data structures should not be accessed simultaneously by different threads.