[OS] Chapter 3 - Process Management

Process

is the execution of a program that performs the actions specified in that program.

Text section

comprises the compiled program code, read in from non-volatile storage when the program is launched.

Data section

stores global and static variables, allocated and initialized prior to executing main.

Heap

is used for dynamic memory allocation, and is managed via calls to new, delete, malloc, free, etc.

Stack

is used for local variables.

Stack overflow

If stack and heap ever meet, then either a __________ error will occur, or else a call to new or malloc will fail due to insufficient memory available.

Process Management

involves various tasks like creation, scheduling, termination of processes, and a dead lock.

Process states

a condition of the process at a specific instant of time. It also defines the current position of the process.

New

process is created when a specific program calls from secondary memory/hard disk to primary memory / RAM.

Ready

the process should be loaded into the primary memory which is ready for execution.

Running

the process is in execution.

Waiting

the process cannot run at the moment, because it is waiting for some resources to become available or for some event to occur.

Terminated or Halted

process has completed.

Context switching

• is the process of saving the context of one process and loading the context of another process.

• In simple terms, it is like loading and unloading the process from running state to ready state.

Context switching

• happens when:

  • When a high-priority process comes to ready state (i.e. with higher priority than the running process)

  • An interrupt occurs

  • User and kernel mode switch (though, this is not necessary)

  • Preemptive CPU scheduling is used.

Context switching

process of saving and restoring the state of a CPU so that multiple processes can share a single CPU resource.

Context switching

are triggered by the OS scheduler, which decides which process should run next based on scheduling policies.

Mode switch, or privilege level switch

refers to the transition of the CPU from one privilege level to another.

Mode switch, or privilege level switch

occurs when CPU privilege level is changed, for example when a system call is made, or a fault occurs.

fork()

duplicates the current process to create a new one in Unix-like operating system.

spawn()

creates a new process or thread, often at a higher level of abstraction, in various programming languages and environments.

Initialization

Operating system prepares for process creation.

Allocation of Process ID (PID)

Unique identifier assigned to the new process.

Memory Allocation

Space allocated for code, data, heap, and stack.

Creation of Process Control Block (PCB)

Data structure initialized to manage the process.

Scheduling

Process scheduled for execution based on OS scheduling policy.

Execution

Process begins executing its instructions.

fork()

to create a child process

exit()

to terminate a child process

wait()

parent process waits for a child process

exec()

process overwrites itself with another executable program

Process termination

occurs when the exit system is called.

Deallocated

When a process exits, resources, memory, and I/O devices are all _________.

Multiple threads

are contained within a process. 

Thread

is the segment of a process which means a process can have multiple threads.

Multithreading

The ability of a program to execute multiple threads concurrently within a single process, allowing for parallel execution of tasks and efficient utilization of resources is called ___________.

Long-term scheduler

(a.k.a. job scheduler) – selects process from the queue and puts them in the memory for it to be executed.

Short-term scheduler

(a.k.a. CPU scheduler) – manages process that are ready to execute and allocates CPU to one of them.

Medium-term scheduler

(a.k.a. swapper) – manages the swapping of processes in the main memory and secondary memory.

Process scheduling

is the process manager’s ability to remove running process from the CPU and selecting another process through a particular strategy.

Main goal of Process Scheduling

• keep the CPU occupied all the time; and 

• provide the least amount of response time for every program.

Two (2) scheduling categories

• Non-preemptive scheduling

• Preemptive scheduling

Arrival Time (AT)

time at which the process arrives in the ready queue.

Completion Time

time at which processes completes its execution.

Burst Time (BT)

time require by a process for CPU execution.

Turn Around Time (TT or TaT)

time difference between completion time and arrival time.

Waiting Time (WT)

time difference between turn around time and burst time.

Non-Preemptive Algorithms

• First Come First Serve (FCFS)

• Shortest Job First (SJF)

• Non-Preemptive Priority (NPP)

Preemptive Algorithms

• Round Robin (RR)

• Shortest Remaining Time First (SRTF)

• Preemptive Priority (PP)