Difference between volatile and synchronized in Java
volatile ensures all threads see the latest value of a single variable. It's great for flags and state reporting without compound actions.
Example:
On the flip side, synchronized offers mutual exclusion, allowing only one thread inside a method or block. Perfect for atomic operations or dealing with multiple variables.
Example:
In a nutshell: use volatile for cost-efficient synchronization of single variables and synchronized for complete thread-safety of compound actions.
Synchronization 101
Understanding volatile
A volatile field guarantees that all threads see a coherent value for the variable, avoiding caching issues without any need for locking. It's like a freshly baked pie always ready for serving.
Grasping synchronized
Unlike volatile, synchronized offers atomicity for compound actions by locking access to a resource. Here, the operations inside the synchronized block are like a bicycle - they only work if all the parts are effectively assembled.
Volatile versus synchronized
While volatile allows multi-threaded reading without locking, synchronized uses intrinsic locks ensuring exclusive access, much like a restroom where only one person can enter at a time!
When to use volatile or synchronized
Single variable use-case
For instant updates to a sensor value or status flag by one thread and read by others - volatile is your go-to keyword!
Multiple variable or compound operation use-case
Got a complicated task like updating account balances? Or changing states of multiple variables? synchronized is the bouncer who ensures atomic execution of your code, keeping your data party crasher-free.
Performance chess game
Understanding your requirements is crucial. volatile is your rook, moving straight efficiently in low latency, but restricted when a complex move (compound action) is needed, that's when your queen, synchronized, steps in with stronger consistency.
Going beyond basics
Pre and post-Java 5 scenario
There was a time when volatile was not particularly strong (pre-Java 5). But post-Java 5, volatile hit the gym and now, together with synchronized, you can trust it for robust thread visibility!
The memory fence
Both volatile and synchronized enforce a happens-before consistency, acting as memory barriers. They ensure that your memory actions (reads/writes) don't get reordered like a shuffled playlist.
Advanced gear for synchronization
Explicit locks utilizing concurrency toolkit
java.util.concurrent.locks package upgrades your intrinsic locks by providing ReentrantLock, ReadWriteLock, and others for more refined control. It's like having a Swiss Army Knife instead of just a plain knife.
Atomic variables for single-variable operations
If you're looking to write lock-free thread-safe code, java.util.concurrent.atomic package is your new best friend. It offers atomic operations on single variables like CAS (compare-and-swap).
Real-time scenarios
The volatile fan club: Gaming and live feeds
In gaming or live data feeds, everyone wants to know what's happening right now, volatile gives them just that - a real-time response without complex state management.
The synchronized party: Finance and workflows
Complex operations like financial transactions and multi-step workflows need a gatekeeper - an atomic operations bouncer - enter synchronized!
Masterclass with Lawrence Dol
Lawrence Dol's "read-write-update" model strikes a balance using volatile for read operations, synchronized for write operations, and explicit locks for update operations - graceful as a ballet dancer.
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