Data Sharing Between Threads

1. The “Why” In multithreading, a Critical Section is any segment of code that accesses a shared resource (like a variable, a file, or a database connection) where at least one thread is performing a write operation. The problem is that most high-level operations (like count++) are not atomic. To the CPU, count++ is actually three distinct steps: Load: Move the value from the Main Memory (Heap) into a CPU Register. Increment: Add 1 to the value inside the Register. Store: Move the new value from the Register back to Main Memory. If Thread A is “paused” (context-switched) after Step 2, and Thread B performs all three steps, Thread A will eventually wake up and overwrite Thread B’s work with an outdated value. This is a Race Condition. ...

1. The “Why” In a multithreaded application, we need to know where data lives to understand its visibility. If data is on the Stack, it is private and safe. If data is on the Heap, it is shared and potentially dangerous. This distinction determines whether we need synchronization (locks/mutexes) or if the code is “thread-safe” by design. 2. Visual Logic Every thread gets its own private Stack, but all threads share a single, massive Heap. ...