Key Insights
# Mass Wakeup
notifyAll() yells “Everybody up!” waking all threads waiting on an object’s monitor—cue the JVM thunderdome.
# No Fairness Guarantee
The JVM scheduler decides who goes next. There’s no VIP line or orderly queue.
# Condition Re-Check
Always re-verify your wait condition in a loop. Skip this, and you’ll debug phantom bugs.
## Common Misunderstandings
# Not a Silver Bullet
Blast every waiting thread, and you get the thundering herd: wasted CPU, longer waits, and frustrated developers.
# Conditions Are King
Mixing multiple predicates under one monitor? A blanket notifyAll() can wake irrelevant threads. Targeted signaling is leaner.
## Modern Trends
# From wait/notify to java.util.concurrent
High-level locks, semaphores, and thread pools in java.util.concurrent abstract away manual signaling.
# Embracing Immutability
Immutable data structures reduce shared-state coordination, slashing the need for mass wakeups.
## Real-World Examples
# Publisher-Subscriber Blast
A publisher pushing updates to all subscribers uses notifyAll()—just make sure everyone actually has work.
# Producer-Consumer Pitfalls
If you only add one item to a queue, notify() is faster. Waking all consumers to fight over nothing is overkill.
Is notifyAll() your secret Java concurrency weapon, or the reason you guzzle coffee during production incidents? Let us know your war stories.
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References:
- https://www.geeksforgeeks.org/java/difference-between-notify-and-notifyall-in-java/
- https://www.digitalocean.com/community/tutorials/java-thread-wait-notify-and-notifyall-in-java
- https://wiki.sei.cmu.edu/confluence/display/java/THI02-J.+Notify+all+waiting+threads+rather+than+a+single+thread
- https://codeinjava.hashnode.dev/understanding-wait-notify-and-notifyall-in-java/
