In concurrent programming and operating systems, what is process synchronization?

Introduction / Context:
When multiple processes or threads run concurrently and share data or resources, their operations can interleave in many different ways. Without proper control, these interleavings can lead to race conditions, inconsistent data and subtle bugs. Process synchronization is the set of techniques used to coordinate concurrent activities to maintain correctness.

Given Data / Assumptions:

There are multiple processes or threads executing at the same time.
They share some data structures, files or hardware resources.
The order in which operations occur can affect the final outcome.
The goal is to preserve data consistency and system correctness.

Concept / Approach:
Process synchronization involves using mechanisms such as locks, semaphores, monitors, condition variables and barriers to control the order and timing of access to shared resources. It ensures that critical sections of code, where shared data is modified, are executed under mutual exclusion and sometimes under ordering constraints. Correct synchronization eliminates harmful race conditions while allowing as much parallelism as possible for performance.

Step-by-Step Solution:
Step 1: Identify critical sections in the code where shared data structures are read or updated by multiple processes. Step 2: Recognize that if two processes enter a critical section at the same time, the resulting interleaving of operations can corrupt the shared state. Step 3: Use synchronization primitives, such as mutexes or semaphores, to ensure that only one process at a time executes the critical section or that operations occur in a well defined order. Step 4: Apply higher level constructs, such as monitors and condition variables, to handle complex coordination patterns like producer consumer, readers writers and barrier synchronization. Step 5: Evaluate the design to ensure that it avoids deadlocks and excessive blocking while still guaranteeing correctness.

Verification / Alternative check:
Operating system and concurrency literature defines process synchronization as coordination of concurrent processes to maintain data consistency and correctness when sharing resources. Compression, backup or permanent mode changes are not mentioned under this term and relate to different aspects of system behaviour.

Why Other Options Are Wrong:
Compressing processes is not a standard term and has nothing to do with controlling execution order.
Backing up processes is related to checkpointing or fault tolerance, not to controlling shared resource access in real time.
Converting a process to kernel mode permanently goes against the protection model and is not the goal of synchronization.

Common Pitfalls:
A frequent mistake is to over synchronize, using locks in a way that severely limits parallelism or introduces deadlocks. Another pitfall is to rely on timing assumptions, such as expecting that one thread will always run faster than another, instead of using proper synchronization primitives.

Final Answer:
Process synchronization is the coordination of processes or threads so that they access shared resources in a controlled order, preventing race conditions and ensuring that the system produces correct and consistent results.