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Today, we're diving into the lifecycle of a process in an operating system. Can anyone tell me what a process is?
A process is when a program is running, right?
Exactly! A process is indeed an active instance of a program. It goes through several states during its lifecycle. Can anyone name those states?
I think there's a New state, a Ready state, and a Running state.
Correct! Those are three states we will discuss today. Remember, we can use the acronym 'N-R-W-W-T' to help us remember: New, Ready, Waiting, and Terminated.
What does each state mean?
Great question! Let's go through each state one by one. Starting with the New state, where a process is created and set up by the operating system.
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In the New state, the operating system allocates resources to the process, assigns it a unique Process ID, and prepares it for execution. Once ready, it transitions to the Ready state. What do you think happens in the Ready state?
The process is now waiting for the CPU to become available!
Exactly! In the Ready state, the process is prepared for execution and is placed in a ready queue. Who can remind us what the short-term scheduler does here?
It picks the next process from the ready queue to run on the CPU.
Correct! Let's summarize: In the New state, processes are created, and in the Ready state, they await CPU execution.
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Now let's shift our focus to the Running state. When a process is in the Running state, what do you suppose is happening?
The CPU is executing its instructions!
Right! The process runs until either it completes, hits a waiting condition, or is preempted. What sort of events might cause a transition to the Waiting state?
Like waiting for I/O operations, like reading from a disk?
Exactly! Waiting often occurs due to I/O operations, resource unavailability, or inter-process communication. After the event, it goes back to the Ready state.
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Finally, letβs discuss the Terminated state. What happens when a process reaches this state?
It means the process has finished executing, right?
Yes, correct! The OS performs cleanup activities like deallocating resources. Why do you think this is important for the OS?
To free memory and resources for new processes!
Exactly! Efficient resource management is vital for effective process handling. Great job today, everyone!
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The section details the different states of a processβincluding New, Ready, Running, Waiting, and Terminatedβhighlighting their significance in process management and the overall functioning of an operating system.
In operating systems, a process is an active instance of a program that transitions through distinct states, which signify its current status. The lifecycle of a process encompasses several states:
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β New (Creation):
β This is the initial state of a process. When a user requests to run a program, or a system call initiates a new process, the operating system begins the process creation routine.
β In this state, the OS performs essential tasks:
β Allocating a unique Process ID (PID).
β Allocating a Process Control Block (PCB) for the process.
β Loading the program code and static data into main memory.
β Setting up the initial stack and heap.
β Initializing process-specific resources and data structures.
β Once these initial setup steps are complete, the process transitions to the Ready state.
The New state is where a process begins its life cycle. When the user wants to run a program, the operating system (OS) creates a new instance of it, known as a process. Several critical tasks are performed during this stage: The OS assigns a unique Process ID (PID), which serves as the process's identity in the system. It also creates a Process Control Block (PCB), which is a data structure that contains important information about the process, such as its state and resource allocations. The program's code and static data are loaded into the system's memory, and the initial requirements for the process's stack (for function calls) and heap (for dynamic memory) are set up. After these steps, the process is ready to be executed and transitions into the Ready state, where it awaits CPU time.
Think of the New state as the moment you order a meal at a restaurant. You are placing your order, and the staff (the operating system) is busy setting everything upβgetting your table ready, assigning your order a unique number (PID), and preparing the ingredients (loading the program into memory). Once everything is prepared, they serve you (transition to the Ready state) and wait for a table to open up (waiting for CPU time).
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β Ready (Waiting for CPU):
β A process in the Ready state has all the necessary resources loaded into main memory and is prepared to execute its instructions.
β It is merely waiting for the CPU to become available and for the short-term scheduler to select it for execution.
β Ready processes are typically maintained in a 'ready queue,' from which the CPU scheduler picks the next process.
In the Ready state, the process has been successfully created and is fully loaded into memory, with all necessary resources in place for it to execute. However, it is not yet running; it simply awaits its turn to use the CPU. The CPU scheduler, which is a part of the operating system, maintains a list of all processes that are ready to execute, known as the ready queue. When the CPU is free to execute a process, the scheduler selects one from this queue and allocates CPU time to it.
Imagine a waiting room in a doctor's office. All the patients (processes) are checked in and ready to see the doctor (CPU). Each patient has all their information prepared, but they need to wait until their name is called (the scheduler picks them) before entering the consultation room (the CPU).
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β Running (Executing on CPU):
β In the Running state, the process's instructions are actively being executed by the CPU.
β On a single-core processor, only one process can be in the Running state at any given instant. Multi-core processors allow multiple processes (or threads) to be in the Running state simultaneously, each on a different core.
β A process remains in this state until:
β Its allocated time slice (quantum) expires (preemption).
β It encounters an event that requires waiting (e.g., I/O request).
β It completes its execution.
β It is forcibly terminated by the operating system or another process.
When a process is in the Running state, it means that its code is currently being executed by the CPUβthis is the active phase of the process's life cycle. On systems with a single CPU core, only one process can be running at any time. However, if there are multiple CPU cores, several processes can run concurrently. A process can stay in this state until one of several conditions occurs: its allocated time slice (time quantum) runs out, it requires input/output operations that make it wait, it finishes its task, or it gets terminated by the OS or another process.
Consider this like a runner participating in a race. While the runner (process) is running, they are actively making progress towards the finish line (executing instructions). However, they might have to stop if they run out of breath (time quantum expires), need a drink (waiting for I/O), finish the race (process completion), or decide to quit (be terminated).
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β Waiting (Blocked - Waiting for Event):
β A process enters the Waiting state when it needs to perform an operation that will take a significant amount of time, during which the CPU cannot be used productively for that process.
β Common reasons for entering the Waiting state include:
β I/O operations: Waiting for data from a hard disk, network, or keyboard input.
β Resource unavailability: Waiting for a lock, a mutex, or another shared resource to become available.
β Inter-process communication: Waiting for a message from another process.
β System calls: Certain system calls (e.g., sleep()) can put a process into a waiting state.
β Processes in this state are typically placed in specific 'wait queues' or 'device queues' associated with the event they are waiting for. Once the event occurs, the operating system moves the process from the Waiting state back to the Ready state.
The Waiting state occurs when a process requires some operation that is not immediately available, meaning it can't continue executing. This might happen for various reasonsβperhaps the process is waiting for data to be read from a disk, for a resource that is currently in use by another process, or for communication from another process. Processes in this state are moved to a wait queue until the event they are waiting for occurs, at which point they will transition back into the Ready state to await CPU time again.
This state can be compared to a car waiting at a traffic light. The car (process) wants to move but canβt until the light turns green (event occurs). While the car is waiting, it cannot continue its journey (hence, it's blocked). Once the light changes, it can proceed again.
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β Terminated (Completion/Abnormal End):
β This is the final state of a process. A process enters the Terminated state when:
β It has completed its execution normally (e.g., a program finishes its tasks and exits).
β It has encountered an error and terminated abnormally (e.g., division by zero, invalid memory access, unhandled exception).
β It has been explicitly killed by another process or the operating system (e.g., user ends a task).
β Upon termination, the operating system performs cleanup activities:
β Deallocating all resources held by the process (memory, open files, I/O devices).
β Removing the PCB.
β Potentially returning an exit status code to the parent process.
The Terminated state signifies the end of a process's life cycle. A process can terminate when it finishes executing its tasks, but it can also end prematurely due to errors or user intervention. Once in this state, the operating system cleans up by deallocating all the resources that were allocated to the process, such as memory and open file descriptors. Additionally, the process's PCB (Process Control Block) is removed, and any exit status code that indicates how the process terminated (successfully or due to an error) can be sent back to the parent process.
Think of this as finishing a project at work. Once you submit it (process completion), you might receive feedback from your manager (exit status code). If something goes wrong, like a mistake in the project, you might just have to stop working on it entirely (abnormal termination). Once the project's done, you clear your desk and archive all materials (cleanup activities).
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Key Concepts
Process States: The various stages a process goes through during its lifecycle.
Process Control Block (PCB): The data structure that keeps track of process information.
Transition Between States: Processes move between different states based on their execution and resource needs.
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When you start Microsoft Word, it transitions from New to Ready, and then to Running as you begin typing.
A game might pause and transition from Running to Waiting while it waits for user input or a server response.
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From New to Ready, then Running we go, Wait for an event, then itβs time to let go.
Once upon a time in the land of Processes, a program named 'App' started its journey as 'New'. App faced challenges but learned to become Ready, executed as Running, paused for I/O in Waiting, and finally fulfilled its purpose in the Terminated stage.
Remember N - R - W - T for New, Ready, Waiting, and Terminated.
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Review the Definitions for terms.
Term: Process
Definition:
An active instance of a program that has its own state, resources, and execution context.
Term: Process Control Block (PCB)
Definition:
A data structure that contains important information about a process, like its state, PID, and memory management details.
Term: New State
Definition:
The initial state of a process during which it is being created and set up.
Term: Ready State
Definition:
A state where the process is loaded in memory and waiting for CPU time.
Term: Running State
Definition:
The state in which the CPU is currently executing the instructions of a process.
Term: Waiting State
Definition:
The state where a process is blocked, waiting for some external event to occur before it can resume execution.
Term: Terminated State
Definition:
The final state of a process after it has completed execution or been killed.