Process Synchronization In Operating System
When many processes run at the same time (for example on a multi-core CPU), they may need to share the same resources or data. This can lead to wrong or inconsistent results if they interfere with each other. Process synchronization ensures that all processes work correctly and safely by coordinating their access using specific techniques.
On the basis of synchronization, processes in an operating system are commonly divided into two main categories:
Independent Process:
The execution of one process does not affect the execution of other processes. They do not share data, resources, or state with any other process. And In this case no need of synchronization because they don’t use common resources.
Cooperating (Dependent) Processes:
The execution of one process can affect the execution of other processes. They share data, files, or other resources and therefore require process synchronization to avoid problems such as race conditions and data inconsistency.
Why It’s Needed?
When several processes (or threads) run at the same time and share data or devices, synchronization is needed. If synchronization is poor or missing, serious problems can occur.
Here are the main problems, explained simply and in detail:
Race Condition:
Two or more processes access and change the same data at the same time, and the final result depends on the unpredictable order of execution. For example, if two processes simultaneously write to the same variable, the final value may be unpredictable or incorrect. It is occur because no proper mutual exclusion in the critical section.
Deadlocks:
A situation where two or more processes wait forever because each is holding a resource and waiting for another that is locked by someone else. Deadlocks occur when processes are unable to proceed because each process is waiting for a resource held by another process, creating a circular dependency. Example: Process A holds a printer and waits for a disk; Process B holds the disk and waits for the printer. Neither can continue.
Starvation:
A process waits for a very long time (maybe forever) because higher-priority processes keep getting the CPU or resources.
Data Inconsistencies:
Inconsistent or incorrect data may occur when processes manipulate shared data concurrently. For example, if multiple processes simultaneously update a database record, the final state of the record may be inconsistent or corrupted.
All the classic synchronization problems—such as race conditions, data inconsistency, deadlock, starvation, priority inversion, and busy waiting—arise inside or because of a critical section when it is not properly protected or synchronized.
- The critical section is the part of a program where shared resources (variables, files, database records, devices) are read or updated. So It is the place where problems like race conditions, deadlock, and starvation can happen.
- And Process synchronization provides the methods and tools to control access to the critical section and avoid those problems.
Goal of Process Synchronization
The main goal is to ensure that multiple processes (or threads) can share resources safely and efficiently. Specifically, process synchronization aims to:
- Preventing Race Conditions: Ensures processes don’t access shared data at the same time, avoiding inconsistent results.
- Provide mutual exclusion: Make sure only one process at a time can enter a critical section.
- Fairness: Prevents starvation by giving all processes fair access to resources.
- Improve system performance: Coordinate CPU and I/O so that processes don’t block each other unnecessarily.
- Deadlock Prevention: Avoids circular waits and indefinite blocking by using proper resource handling.
- Safe Communication: Ensures data/messages between processes are sent, received and processed in order.
Solutions to Process Synchronization Problems
In a multiprogramming environment, multiple processes often compete for shared resources such as memory, CPU, or files. If not managed properly, this can lead to problems like race conditions, deadlocks, and data inconsistency. To avoid such issues, process synchronization provides techniques to control access and keep data consistent.
Over the years, different solutions have been proposed—each improving on earlier approaches—and these are generally grouped into three major levels: software (algorithmic), hardware (low-level), and operating system/high-level.
1. Software Level:
The software (algorithmic) level of process synchronization provides pure programming techniques, such as Peterson’s algorithm and the Bakery algorithm, to protect critical sections. They are theoretical foundations for mutual exclusion and fairness—still important for learning, though modern systems typically rely on faster hardware or OS-level solutions.
- Peterson’s Algorithm – works for two processes using flag and turn.
- Bakery Algorithm – works for multiple processes using numbered tickets.
2. Hardware (low-level) Level
At this level, the CPU itself provides special machine instructions that can perform certain read-modify-write operations in one unbreakable (atomic) step. These instructions let the operating system (or a program) lock and unlock a critical section safely without relying on slow software-only tricks.
- Test-and-Set (TSL)
- Compare-and-Swap (CAS)
- Interrupt Disabling
3. Operating System (high-level) Level
At this level, the operating system and programming languages provide built-in synchronization primitives. These are ready-to-use mechanisms that hide low-level hardware details and make it easier and safer to coordinate multiple processes or threads.
- Semaphores
- Mutex Locks (Mutual Exclusion Locks)
- Monitors / Condition Variables