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Both synchronized and ReentrantLock are used for mutual exclusion in Java (i.e., only one thread can execute a critical section at a time), but they have key differences in capabilities, flexibility, and usage style.

🧹🧵 When Should You Call threadLocal.remove()?

✅ 1. When you’re done with the thread-local value

If your thread is long-lived (like in a thread pool), you must clean up the thread-local variable after you’re done using it.

🧵🔐 What is a ThreadLocal Variable?

A ThreadLocal is a special Java class that provides thread-local storage.

📌 Each thread that accesses a ThreadLocal variable gets its own independent copy of the variable.

So even though many threads use the same ThreadLocal instance, each thread interacts only with its own isolated value.

🧵🛠️ How to Dump Threads in Java

✅ 1. Using Command-Line Tools

🔸 A) jstack — Most Common

jstack <PID>

Dumps all thread stack traces of a running JVM.

🔍 In the Java Virtual Machine (JVM), you can control the size of each thread’s stack using the following startup parameter:

✅ Ways to Share Data Between Threads in Java

Let’s go step by step from simple to advanced.

🧠 Stack vs Heap in Multithreading

🔍 Stack (Per Thread)

Each thread has its own stack where it stores:

• Method call frames
• Local variables (primitives and references)
• Return addresses

No two threads share the same stack, so: ✔️ No synchronization needed ✔️ Very fast access

Java has a modern async feature very similar to Promises in TypeScript, and it’s called CompletableFuture — it lets you run tasks asynchronously without blocking the main thread and chain actions just like promises.

🔁 Callable vs Runnable

Let’s compare submit() and execute() clearly — both are used to hand over tasks to a thread pool, but they behave differently in a few key areas.

✅ 1. Return Type

• submit() gives you a Future object — you can use it to:
  • Check if the task is done
  • Cancel the task
  • Get the result (or exception, if any)