Concurrency & Parallelism in Software Engineering

A process is an independent, isolated execution environment with its own memory space allocated by the OS. A thread is the smallest unit of execution within a process that shares memory and resources with other threads in the same process.

Concurrency is about dealing with multiple tasks at once by interleaving execution on a single core or multiple cores. Parallelism is about doing multiple tasks simultaneously on physical multi-core hardware.

A flaw that occurs when a system's output depends on the non-deterministic sequence or timing of uncontrollable execution events (such as thread scheduling), leading to unpredictable behavior.

A code segment that accesses shared resources (like global variables or files) and must not be executed by more than one thread concurrently to prevent race conditions.

A synchronization mechanism that grants exclusive access to a shared resource to a single thread at a time. Threads must lock the mutex before entering a critical section and unlock it upon exit.

A Binary Semaphore has a state of 0 or 1 and works similarly to a mutex. A Counting Semaphore maintains an integer counter to control access to a finite pool of shared resources.

A situation where a set of threads are blocked permanently because each thread holds a resource that another thread requires, forming a circular dependency.

1. Mutual Exclusion: Resources cannot be shared.
2. Hold and Wait: Threads hold resources while waiting for others.
3. No Preemption: Resources cannot be forcibly taken from threads.
4. Circular Wait: A closed chain of threads exists where each waits for a resource held by the next.