Does ConcurrentHashMap uses object level lock?

ConcurrentHashMap was introduced in JDK 5. There is no locking at the object level,The locking is at a much finer granularity.

Which lock is used in ConcurrentHashMap?

In ConcurrentHashMap, at a time any number of threads can perform retrieval operation but for updated in the object, the thread must lock the particular segment in which the thread wants to operate. This type of locking mechanism is known as Segment locking or bucket locking.

Is ConcurrentHashMap uses object level lock for synchronizing access by multiple thread?

There is no locking at the object level. The locking is at a much finer granularity at a hashmap bucket level. ConcurrentHashMap doesn't throw a ConcurrentModificationException if one thread tries to modify it while another is iterating over it. ConcurrentHashMap uses multitude of locks.

Does ConcurrentHashMap only use one lock?

Yes, ConcurrentHashMap uses a multitude of locks (by default, 16 of them), each lock controls one segment of the hash.

Does ConcurrentHashMap use Read Write lock?

So unlike hashtable, we perform any sort of operation ( update ,delete ,read ,create) without locking on entire map in ConcurrentHashMap. Retrieval operations (including get) generally do not block. It uses the concept of volatile in this case., so may overlap with update operations (including put and remove).

ConcurrentHashMap How It Works Internally. Asked by tech companies in phone screen interview rounds.

How does ConcurrentHashMap locking implemented work?

ConcurrentHashMap: It allows concurrent access to the map. Part of the map called Segment (internal data structure) is only getting locked while adding or updating the map. So ConcurrentHashMap allows concurrent threads to read the value without locking at all. This data structure was introduced to improve performance.

What is difference between synchronizedMap and ConcurrentHashMap?

synchronizedMap() requires each thread to acquire a lock on the entire object for both read/write operations. By comparison, the ConcurrentHashMap allows threads to acquire locks on separate segments of the collection, and make modifications at the same time.

What is difference between ConcurrentHashMap and HashMap?

HashMap is non-Synchronized in nature i.e. HashMap is not Thread-safe whereas ConcurrentHashMap is Thread-safe in nature. HashMap performance is relatively high because it is non-synchronized in nature and any number of threads can perform simultaneously.

How does ConcurrentHashMap achieve scalability?

Unlike Hashtable which achieves its thread-safety by compromising the scalability, ConcurrentHashMap uses advanced techniques e.g. dividing the map into segments to remain thread-safe and scalable at the same time.

What is difference between Hashtable and ConcurrentHashMap in Java?

Hashtable is belongs to the Collection framework; ConcurrentHashMap belongs to the Executor framework. Hashtable uses single lock for whole data. ConcurrentHashMap uses multiple locks on segment level (16 by default) instead of object level i.e. whole Map . ConcurrentHashMap locking is applied only for updates.

How is ConcurrentHashMap thread-safe?

ConcurrentHashMap class achieves thread-safety by dividing the map into segments, the lock is required not for the entire object but for one segment, i.e one thread requires a lock of one segment. In ConcurrenHashap the read operation doesn't require any lock.

What is class level lock and object lock?

Class level lock is achieved by keyword "Static Synchronized,where as object level is achieved only by synchronized keyword. Object level lock is achieved to restrict same object to operate through different thread,where as class level lock is achieved to restrict any object to operate.

Can ConcurrentHashMap throws ConcurrentModificationException?

ConcurrentHashMap does not throw ConcurrentModificationException if the underlying collection is modified during an iteration is in progress. Iterators may not reflect the exact state of the collection if it is being modified concurrently. It may reflect the state when it was created and at some moment later.

Does ConcurrentHashMap allow null values?

The main reason that nulls aren't allowed in ConcurrentMaps (ConcurrentHashMaps, ConcurrentSkipListMaps) is that ambiguities that may be just barely tolerable in non-concurrent maps can't be accommodated. The main one is that if map.

What is concurrency level?

So,concurrency level is the equal to to the writer threads. And map will also segmented equals to the value of concurrency level. Follow this answer to receive notifications.

How will you ensure that your read/write solution is scalable and thread safe?

So, the only way to achieve scalability and thread safety is to find independent parts in your data. And then, update them in parallel from multiple threads.

What are concurrent collections in Java?

The concurrent collection APIs, apart from the Java Collection API, are a set of collections APIs that are designed and optimized specifically for synchronized multithreaded access. They are grouped under the java. util. concurrent package.

Which is known as the thread safe implementation of the Hashmap provides the full concurrency to retrieve and high expected concurrency of updates?

A hash table supporting full concurrency of retrievals and high expected concurrency for updates. This class obeys the same functional specification as Hashtable and includes versions of methods corresponding to each method of Hashtable.

Why ConcurrentHashMap is fail safe?

This is because, they operate on the clone of the collection, not on the original collection and that's why they are called fail-safe iterators. Iterator on CopyOnWriteArrayList, ConcurrentHashMap classes are examples of fail-safe Iterator.

Is HashMap faster than ConcurrentHashMap?

The summary

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.

Can we replace Hashtable with ConcurrentHashMap?

Is it safe to replace the Hashtable instances with ConcurrentHashmap instances for performance gain? In most cases it should be safe and yield better performance. The effort on changing depends on whether you used the Map interface or Hashtable directly.

Is ConcurrentHashMap sorted?

you can't sort a ConcurrentHashMap at all. you would have to use an alternate data structure if you want to sort (by key or by value).

What is the best benefit of using a ConcurrentHashMap instead of a HashMap?

Advantages of ConcurrentHashMap over HashMap

The advantages of using ConcurrentHashMap are as follows: It provides very high concurrency in a multi-threaded environment. The read operation can be very fast when the write operation is done with a lock. It provides No object-level Locking.

Is LinkedHashMap synchronized?

Just like HashMap, LinkedHashMap implementation is not synchronized. So if you are going to access it from multiple threads and at least one of these threads is likely to change it structurally, then it must be externally synchronized.