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Process management- This ppt contains all required information regarding operating system processes, threads.

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ApurvaLaddha

The document discusses processes and process management. It defines a process as an active program in execution. Processes fall into two categories - system processes started by the OS and user processes started by the user. Each process runs independently and has its own memory space. Process management allows controlling processes by starting, ending, and setting priorities. Processes pass through states like new, ready, running, wait, and termination. The OS performs operations on processes like creation, scheduling, execution, and deletion. Schedulers like long-term, short-term, and medium-term manage processes. A process control block tracks process information.

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UNIT 2 PROCESS MANAGEMENT By Apurva Bijawe
PROCESS • A process is a program in execution. For example, when we write a program in C or C++ and compile it, the compiler creates binary code. The original code and binary code are both programs. • When we actually run the binary code, it becomes a process. • A process is an ‘active’ entity instead of a program, which is considered a ‘passive’ entity. • A single program can create many processes when run multiple times; for example, when we open a .exe or binary file multiple times, multiple instances begin (multiple processes are created). WHAT IS PROCESS? 2
PROCESSES USUALLY FALL INTO TWO CATEGORIES 1. System processes • System processes are started by the operating system, and they usually have something to do with running the OS itself. 2. User processes • User processes, as you might guess, are those that the user starts. The operating system though handles various system processes, but it mainly handles the user code execution. • Each process can run independently of other processes and have its own memory space. This makes process management tricky, as the OS needs to ensure that each process gets its fair share of resources (memory, CPU time, etc.) while ensuring that the system remains stable. 3
WHAT IS PROCESS MANAGEMENT? • It is an important part of the operating system. • It allows you to control the way your computer runs by managing the currently active processes. This includes ending processes that are no longer needed, setting process priorities, and more. 4
PROCESS STATES 5
• The process, from its creation to completion, passes through various states. The minimum number of states is five. • The names of the states are not standardized although the process may be in one of the following states during execution. 1. New • A program which is going to be picked up by the OS into the main memory is called a new process. 2. Ready • Whenever a process is created, it directly enters in the ready state, in which, it waits for the CPU to be assigned. The OS picks the new processes from the secondary memory and put all of them in the main memory. • The processes which are ready for the execution and reside in the main memory are called ready state processes. There can be many processes present in the ready state. 6
3. Running • One of the processes from the ready state will be chosen by the OS depending upon the scheduling algorithm. Hence, if we have only one CPU in our system, the number of running processes for a particular time will always be one. If we have n processors in the system then we can have n processes running simultaneously. 4. Block or wait • From the Running state, a process can make the transition to the block or wait state depending upon the scheduling algorithm or the intrinsic behavior of the process. • When a process waits for a certain resource to be assigned or for the input from the user then the OS move this process to the block or wait state and assigns the CPU to the other processes. 5. Completion or termination • When a process finishes its execution, it comes in the termination state. All the context of the process (Process Control Block) will also be deleted the process will be terminated by the Operating system. 7
6. Suspend ready • A process in the ready state, which is moved to secondary memory from the main memory due to lack of the resources (mainly primary memory) is called in the suspend ready state. • If the main memory is full and a higher priority process comes for the execution then the OS have to make the room for the process in the main memory by throwing the lower priority process out into the secondary memory. The suspend ready processes remain in the secondary memory until the main memory gets available. 7. Suspend wait • Instead of removing the process from the ready queue, it's better to remove the blocked process which is waiting for some resources in the main memory. Since it is already waiting for some resource to get available hence it is better if it waits in the secondary memory and make room for the higher priority process. These processes complete their execution once the main memory gets available and their wait is finished. 8
OPERATIONS ON THE PROCESS 1. Creation • Once the process is created, it will be ready and come into the ready queue (main memory) and will be ready for the execution. 2. Scheduling • Out of the many processes present in the ready queue, the Operating system chooses one process and start executing it. Selecting the process which is to be executed next, is known as scheduling. 9
3. Execution • Once the process is scheduled for the execution, the processor starts executing it. Process may come to the blocked or wait state during the execution then in that case the processor starts executing the other processes. 4. Deletion/killing • Once the purpose of the process gets over then the OS will kill the process. The Context of the process (PCB) will be deleted and the process gets terminated by the Operating system. 10
TYPES OF SCHEDULERS 1.Long-term – performance: • It brings the new process to the ‘Ready State’. It controls the Degree of Multi-programming, i.e., the number of processes present in a ready state at any point in time. • It is important that the long-term scheduler make a careful selection of both I/O and CPU-bound processes. I/O-bound tasks are which use much of their time in input and output operations while CPU-bound processes are which spend their time on the CPU. • The job scheduler increases efficiency by maintaining a balance between the two. They operate at a high level and are typically used in batch-processing systems • A long-term scheduler, also known as a job scheduler, is an operating system component that determines which processes should be admitted to the system and when. • The long-term scheduler is in charge of allocating resources such as processor time and memory to processes based on their needs and priorities. It also determines the order in which processes are executed and manages the execution of processes that may take a long time to complete, such as batch jobs or background tasks 11
FUNCTIONS OF LONG-TERM SCHEDULER • Long-term schedulers are in charge of determining the order in which processes are executed and managing the execution of processes that may take a long time to complete, such as batch jobs or background tasks. • A long-term scheduler’s primary function is to minimize processing time by taking the mixtures of CPU-bound jobs and I/O-bound jobs. • CPU Bound Jobs: CPU-bound jobs are tasks or processes that necessitate a significant amount of CPU processing time and resources (Central Processing Unit). These jobs can put a significant strain on the CPU, affecting system performance and responsiveness. • I/O Bound Jobs: I/O bound jobs are tasks or processes that necessitate a large number of input/output (I/O) operations, such as reading and writing to discs or networks. These jobs are less dependent on the CPU and can put a greater strain on the system’s I/O subsystem. 12
13 2.Short-term – Context switching time: It is responsible for selecting one process from the ready state for scheduling it on the running state. Note: Short-term scheduler only selects the process to schedule it doesn’t load the process on running. Short-term scheduler will decide which process is to be executed next and then it will call the dispatcher. A dispatcher is a software that moves the process from ready to run and vice versa. In other words, it is context switching. It runs frequently. Short-term scheduler is also called CPU scheduler.
• Medium-term – Swapping time: Typically, processes that are blocked or waiting must be managed by the medium-term scheduler. • Suspension decision is taken by the medium-term scheduler. The medium-term scheduler is used for swapping which is moving the process from main memory to secondary and vice versa. The swapping is done to reduce degree of multiprogramming. 14
15 COMPARISON AMONG SCHEDULER LongTerm Scheduler Short term schedular MediumTerm Scheduler • It is a job scheduler It is a CPU scheduler It is a process-swapping scheduler. • Generally, Speed is lesser than short term scheduler Speed is the fastest among all of them. Speed lies in between both short and long- term schedulers. • It controls the degree of multiprogramming It gives less control over how much multiprogramming is done. It reduces the degree of multiprogramming.
16 • It is barely present or nonexistent in the time-sharing system. It is a minimal time- sharing system. It is a component of systems for time sharing. • It can re-enter the process into memory, allowing for the continuation of execution. It selects those processes which are ready to execute It can re-introduce the process into memory and execution can be continued.
WHAT IS PROCESS CONTROL BLOCK (PCB)? • Process Control Block is a data structure that contains information of the process related to it. The process control block is also known as a task control block, entry of the process table, etc. • While creating a process, the operating system performs several operations. To identify the processes, it assigns a process identification number (PID) to each process. • As the operating system supports multi-programming, it needs to keep track of all the processes. For this task, the process control block (PCB) is used to track the process’s execution status. Each block of memory contains information about the process state, program counter, stack pointer, status of opened files, scheduling algorithms, etc. • All this information is required and must be saved when the process is switched from one state to another. When the process makes a transition from one state to another, the operating system must update information in the process’s PCB. A process control block (PCB) contains information about the process, i.e. registers, quantum, priority, etc. 17
STRUCTURE OF THE PROCESS CONTROL BLOCK 18
SOME OF DATA ITEMS: 1.Process State • This specifies the process state i.e. new, ready, running, waiting or terminated. 2.Process Number • This shows the number of the particular process. 3.Program Counter • This contains the address of the next instruction that needs to be executed in the process. 4.Registers • This specifies the registers that are used by the process. They may include accumulators, index registers, stack pointers, general purpose registers etc. 5.List of Open Files • These are the different files that are associated with the process 19
6. CPU Scheduling Information • The process priority, pointers to scheduling queues etc. is the CPU scheduling information that is contained in the PCB. This may also include any other scheduling parameters. 7.Memory Management Information • The memory management information includes the page tables or the segment tables depending on the memory system used. It also contains the value of the base registers, limit registers etc. 8.I/O Status Information • This information includes the list of I/O devices used by the process, the list of files etc. 9.Accounting information • The time limits, account numbers, amount of CPU used, process numbers etc. are all a part of the PCB accounting information. 10.Location of the Process Control Block • The process control block is kept in a memory area that is protected from the normal user access. This is done because it contains important process information. Some of the operating systems place the PCB at the beginning of the kernel stack for the process as it is a safe location. 20
PROCESSES ANDTHREADS • Processes: • A process is a program in execution. It consists of: 1.Program Counter (PC): Indicates the address of the next instruction to be executed. 2.Registers: Contain various data, including the current status of the process. 3.Memory Space: Includes code, data, and a stack. • Key characteristics of processes: • Isolation: Processes are isolated from each other, meaning one process cannot directly access the memory of another. • Independence: Processes operate independently, and the failure of one process does not affect others. • Resource Allocation: Each process has its own system resources, such as memory space, file descriptors, etc. 21
• Threads: • A thread is a basic unit of CPU utilization within a process. A process can have multiple threads, and these threads share the same resources (like memory space) but run independently. Threads within the same process can communicate more easily than separate processes. • Key characteristics of threads: • Shared Resources: Threads within the same process share resources like code, data, and files. • Fast Communication: Inter-thread communication is faster than inter-process communication since threads share the same memory space. • Lightweight: Threads are generally more lightweight than processes, as they share resources. 22
The process can be split down into so many threads. For example, in a browser, many tabs can be viewed as threads. MS Word uses many threads - formatting text from one thread, processing input from another thread, etc.
Multithreading in Operating System • A multithreading operating system is one that allows multiple threads to execute concurrently within a single process. This type of OS takes advantage of CPU cores with multiple threads, dividing process execution efficiently to increase the performance of multi-core processors. Each thread runs a part of a process's workload, making the overall execution faster and more efficient. • In such systems, context switching between threads is typically faster than between processes, as threads share the same memory space and resources, whereas processes do not. This sharing enables threads to communicate with each other more quickly than separate processes. • Multithreading is beneficial for tasks that can be divided into smaller, concurrent operations, and it's essential for modern applications that require real-time performance and high responsiveness. This operating system design is widely used in server and desktop applications, where it maximizes resource utilization and provides improved performance on multi-core CPUs. 24
HOW DOES MULTITHREADING IN OS WORK? • Multithreading in an operating system works by allowing multiple threads to exist within the context of a single process, sharing its resources but operating independently. • Think of it like a team of chefs working in one kitchen; they share the same space and utensils (the process's resources), but each chef prepares a different dish simultaneously (the threads). • The operating system manages these threads, scheduling them to run on the CPU in a way that maximizes efficiency—making sure that while one chef is waiting for the oven, another is chopping vegetables. This multitasking nature of threads can lead to faster execution of complex tasks, better resource utilization. 25
REAL WORLD EXAMPLE OF MULTITHREADING • Imagine you are a chef working in a busy kitchen (representing the operating system), and you have multiple tasks to accomplish (representing processes or threads). Each task involves preparing a different dish, and each dish has several steps. • Without multithreading (single-threaded model): • You, as the chef, start preparing one dish at a time. While waiting for one dish to cook, you are idle and cannot work on another dish. • The kitchen is not efficiently utilized, and the overall cooking time is longer because each dish must be completed before starting the next. 26
27 With multithreading (multithreaded model): •You decide to use multiple cutting boards and cooking stations to work on multiple dishes simultaneously. •While one dish is simmering on the stove, you are chopping vegetables for another dish or preparing ingredients for a third dish. •This allows you to make progress on multiple tasks concurrently, making better use of your time and the kitchen resources. •As one dish is completed, you can move on to the next without waiting for the others to finish.
28 In this analogy: Each dish is analogous to a thread or process. The chef represents the operating system. The kitchen resources (cutting boards, cooking stations) represent the CPU and other system resources. Multithreading in the operating system works similarly. Multiple threads or processes can execute concurrently, allowing for better resource utilization and improved overall system performance. Each thread can perform a specific task independently, and the operating system manages their execution, scheduling them to run on the available CPU cores efficiently.
ADVANTAGES OF MULTITHREADING OPERATING SYSTEM • Resource sharing: Because threads can share any process memory and resources, every program can perform several tasks inside the same address space. • Multiple Processor Architecture: Different threads can execute in parallel on many processors, allowing for high processor usage and efficiency. • Reduced Context Switching Time: As with Thread Context Switching, the threads reduce context switching time while keeping the virtual memory space the same. • Cost-effective: Allocating memory and resources throughout the process generation process has a cost. Context-switch threads are more affordable to construct since they can distribute process resources. 29
DISADVANTAGES OF MULTITHREADING OPERATING SYSTEM 1. Complexity and Synchronization • Multithreading introduces complexity into program design and implementation. Coordinating and synchronizing threads to avoid race conditions, deadlocks, and other concurrency-related issues can be challenging. • Debugging multithreaded programs can be more difficult due to the non-deterministic nature of thread execution. 2. Race Conditions • Race conditions occur when multiple threads access shared data concurrently without proper synchronization, leading to unpredictable and erroneous behavior. • Ensuring data consistency and avoiding race conditions requires careful use of synchronization mechanisms like locks and semaphores. 30
31 3. Deadlocks: •A deadlock is a situation where two or more threads are unable to proceed because each is waiting for the other to release a resource. Deadlocks can lead to a complete system halt. •Designing systems to avoid deadlocks requires a good understanding of resource allocation and proper use of synchronization. 4. Thread Starvation and Priority Inversion: •Thread starvation occurs when a thread is unable to access resources or CPU time, potentially leading to poor performance. •Priority inversion occurs when a low-priority thread holds a resource needed by a high-priority thread, leading to the inversion of execution priorities.

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Process management- This ppt contains all required information regarding operating system processes, threads.

  • 2. PROCESS • A process is a program in execution. For example, when we write a program in C or C++ and compile it, the compiler creates binary code. The original code and binary code are both programs. • When we actually run the binary code, it becomes a process. • A process is an ‘active’ entity instead of a program, which is considered a ‘passive’ entity. • A single program can create many processes when run multiple times; for example, when we open a .exe or binary file multiple times, multiple instances begin (multiple processes are created). WHAT IS PROCESS? 2
  • 3. PROCESSES USUALLY FALL INTO TWO CATEGORIES 1. System processes • System processes are started by the operating system, and they usually have something to do with running the OS itself. 2. User processes • User processes, as you might guess, are those that the user starts. The operating system though handles various system processes, but it mainly handles the user code execution. • Each process can run independently of other processes and have its own memory space. This makes process management tricky, as the OS needs to ensure that each process gets its fair share of resources (memory, CPU time, etc.) while ensuring that the system remains stable. 3
  • 4. WHAT IS PROCESS MANAGEMENT? • It is an important part of the operating system. • It allows you to control the way your computer runs by managing the currently active processes. This includes ending processes that are no longer needed, setting process priorities, and more. 4
  • 6. • The process, from its creation to completion, passes through various states. The minimum number of states is five. • The names of the states are not standardized although the process may be in one of the following states during execution. 1. New • A program which is going to be picked up by the OS into the main memory is called a new process. 2. Ready • Whenever a process is created, it directly enters in the ready state, in which, it waits for the CPU to be assigned. The OS picks the new processes from the secondary memory and put all of them in the main memory. • The processes which are ready for the execution and reside in the main memory are called ready state processes. There can be many processes present in the ready state. 6
  • 7. 3. Running • One of the processes from the ready state will be chosen by the OS depending upon the scheduling algorithm. Hence, if we have only one CPU in our system, the number of running processes for a particular time will always be one. If we have n processors in the system then we can have n processes running simultaneously. 4. Block or wait • From the Running state, a process can make the transition to the block or wait state depending upon the scheduling algorithm or the intrinsic behavior of the process. • When a process waits for a certain resource to be assigned or for the input from the user then the OS move this process to the block or wait state and assigns the CPU to the other processes. 5. Completion or termination • When a process finishes its execution, it comes in the termination state. All the context of the process (Process Control Block) will also be deleted the process will be terminated by the Operating system. 7
  • 8. 6. Suspend ready • A process in the ready state, which is moved to secondary memory from the main memory due to lack of the resources (mainly primary memory) is called in the suspend ready state. • If the main memory is full and a higher priority process comes for the execution then the OS have to make the room for the process in the main memory by throwing the lower priority process out into the secondary memory. The suspend ready processes remain in the secondary memory until the main memory gets available. 7. Suspend wait • Instead of removing the process from the ready queue, it's better to remove the blocked process which is waiting for some resources in the main memory. Since it is already waiting for some resource to get available hence it is better if it waits in the secondary memory and make room for the higher priority process. These processes complete their execution once the main memory gets available and their wait is finished. 8
  • 9. OPERATIONS ON THE PROCESS 1. Creation • Once the process is created, it will be ready and come into the ready queue (main memory) and will be ready for the execution. 2. Scheduling • Out of the many processes present in the ready queue, the Operating system chooses one process and start executing it. Selecting the process which is to be executed next, is known as scheduling. 9
  • 10. 3. Execution • Once the process is scheduled for the execution, the processor starts executing it. Process may come to the blocked or wait state during the execution then in that case the processor starts executing the other processes. 4. Deletion/killing • Once the purpose of the process gets over then the OS will kill the process. The Context of the process (PCB) will be deleted and the process gets terminated by the Operating system. 10
  • 11. TYPES OF SCHEDULERS 1.Long-term – performance: • It brings the new process to the ‘Ready State’. It controls the Degree of Multi-programming, i.e., the number of processes present in a ready state at any point in time. • It is important that the long-term scheduler make a careful selection of both I/O and CPU-bound processes. I/O-bound tasks are which use much of their time in input and output operations while CPU-bound processes are which spend their time on the CPU. • The job scheduler increases efficiency by maintaining a balance between the two. They operate at a high level and are typically used in batch-processing systems • A long-term scheduler, also known as a job scheduler, is an operating system component that determines which processes should be admitted to the system and when. • The long-term scheduler is in charge of allocating resources such as processor time and memory to processes based on their needs and priorities. It also determines the order in which processes are executed and manages the execution of processes that may take a long time to complete, such as batch jobs or background tasks 11
  • 12. FUNCTIONS OF LONG-TERM SCHEDULER • Long-term schedulers are in charge of determining the order in which processes are executed and managing the execution of processes that may take a long time to complete, such as batch jobs or background tasks. • A long-term scheduler’s primary function is to minimize processing time by taking the mixtures of CPU-bound jobs and I/O-bound jobs. • CPU Bound Jobs: CPU-bound jobs are tasks or processes that necessitate a significant amount of CPU processing time and resources (Central Processing Unit). These jobs can put a significant strain on the CPU, affecting system performance and responsiveness. • I/O Bound Jobs: I/O bound jobs are tasks or processes that necessitate a large number of input/output (I/O) operations, such as reading and writing to discs or networks. These jobs are less dependent on the CPU and can put a greater strain on the system’s I/O subsystem. 12
  • 13. 13 2.Short-term – Context switching time: It is responsible for selecting one process from the ready state for scheduling it on the running state. Note: Short-term scheduler only selects the process to schedule it doesn’t load the process on running. Short-term scheduler will decide which process is to be executed next and then it will call the dispatcher. A dispatcher is a software that moves the process from ready to run and vice versa. In other words, it is context switching. It runs frequently. Short-term scheduler is also called CPU scheduler.
  • 14. • Medium-term – Swapping time: Typically, processes that are blocked or waiting must be managed by the medium-term scheduler. • Suspension decision is taken by the medium-term scheduler. The medium-term scheduler is used for swapping which is moving the process from main memory to secondary and vice versa. The swapping is done to reduce degree of multiprogramming. 14
  • 15. 15 COMPARISON AMONG SCHEDULER LongTerm Scheduler Short term schedular MediumTerm Scheduler • It is a job scheduler It is a CPU scheduler It is a process-swapping scheduler. • Generally, Speed is lesser than short term scheduler Speed is the fastest among all of them. Speed lies in between both short and long- term schedulers. • It controls the degree of multiprogramming It gives less control over how much multiprogramming is done. It reduces the degree of multiprogramming.
  • 16. 16 • It is barely present or nonexistent in the time-sharing system. It is a minimal time- sharing system. It is a component of systems for time sharing. • It can re-enter the process into memory, allowing for the continuation of execution. It selects those processes which are ready to execute It can re-introduce the process into memory and execution can be continued.
  • 17. WHAT IS PROCESS CONTROL BLOCK (PCB)? • Process Control Block is a data structure that contains information of the process related to it. The process control block is also known as a task control block, entry of the process table, etc. • While creating a process, the operating system performs several operations. To identify the processes, it assigns a process identification number (PID) to each process. • As the operating system supports multi-programming, it needs to keep track of all the processes. For this task, the process control block (PCB) is used to track the process’s execution status. Each block of memory contains information about the process state, program counter, stack pointer, status of opened files, scheduling algorithms, etc. • All this information is required and must be saved when the process is switched from one state to another. When the process makes a transition from one state to another, the operating system must update information in the process’s PCB. A process control block (PCB) contains information about the process, i.e. registers, quantum, priority, etc. 17
  • 18. STRUCTURE OF THE PROCESS CONTROL BLOCK 18
  • 19. SOME OF DATA ITEMS: 1.Process State • This specifies the process state i.e. new, ready, running, waiting or terminated. 2.Process Number • This shows the number of the particular process. 3.Program Counter • This contains the address of the next instruction that needs to be executed in the process. 4.Registers • This specifies the registers that are used by the process. They may include accumulators, index registers, stack pointers, general purpose registers etc. 5.List of Open Files • These are the different files that are associated with the process 19
  • 20. 6. CPU Scheduling Information • The process priority, pointers to scheduling queues etc. is the CPU scheduling information that is contained in the PCB. This may also include any other scheduling parameters. 7.Memory Management Information • The memory management information includes the page tables or the segment tables depending on the memory system used. It also contains the value of the base registers, limit registers etc. 8.I/O Status Information • This information includes the list of I/O devices used by the process, the list of files etc. 9.Accounting information • The time limits, account numbers, amount of CPU used, process numbers etc. are all a part of the PCB accounting information. 10.Location of the Process Control Block • The process control block is kept in a memory area that is protected from the normal user access. This is done because it contains important process information. Some of the operating systems place the PCB at the beginning of the kernel stack for the process as it is a safe location. 20
  • 21. PROCESSES ANDTHREADS • Processes: • A process is a program in execution. It consists of: 1.Program Counter (PC): Indicates the address of the next instruction to be executed. 2.Registers: Contain various data, including the current status of the process. 3.Memory Space: Includes code, data, and a stack. • Key characteristics of processes: • Isolation: Processes are isolated from each other, meaning one process cannot directly access the memory of another. • Independence: Processes operate independently, and the failure of one process does not affect others. • Resource Allocation: Each process has its own system resources, such as memory space, file descriptors, etc. 21
  • 22. • Threads: • A thread is a basic unit of CPU utilization within a process. A process can have multiple threads, and these threads share the same resources (like memory space) but run independently. Threads within the same process can communicate more easily than separate processes. • Key characteristics of threads: • Shared Resources: Threads within the same process share resources like code, data, and files. • Fast Communication: Inter-thread communication is faster than inter-process communication since threads share the same memory space. • Lightweight: Threads are generally more lightweight than processes, as they share resources. 22
  • 23. The process can be split down into so many threads. For example, in a browser, many tabs can be viewed as threads. MS Word uses many threads - formatting text from one thread, processing input from another thread, etc.
  • 24. Multithreading in Operating System • A multithreading operating system is one that allows multiple threads to execute concurrently within a single process. This type of OS takes advantage of CPU cores with multiple threads, dividing process execution efficiently to increase the performance of multi-core processors. Each thread runs a part of a process's workload, making the overall execution faster and more efficient. • In such systems, context switching between threads is typically faster than between processes, as threads share the same memory space and resources, whereas processes do not. This sharing enables threads to communicate with each other more quickly than separate processes. • Multithreading is beneficial for tasks that can be divided into smaller, concurrent operations, and it's essential for modern applications that require real-time performance and high responsiveness. This operating system design is widely used in server and desktop applications, where it maximizes resource utilization and provides improved performance on multi-core CPUs. 24
  • 25. HOW DOES MULTITHREADING IN OS WORK? • Multithreading in an operating system works by allowing multiple threads to exist within the context of a single process, sharing its resources but operating independently. • Think of it like a team of chefs working in one kitchen; they share the same space and utensils (the process's resources), but each chef prepares a different dish simultaneously (the threads). • The operating system manages these threads, scheduling them to run on the CPU in a way that maximizes efficiency—making sure that while one chef is waiting for the oven, another is chopping vegetables. This multitasking nature of threads can lead to faster execution of complex tasks, better resource utilization. 25
  • 26. REAL WORLD EXAMPLE OF MULTITHREADING • Imagine you are a chef working in a busy kitchen (representing the operating system), and you have multiple tasks to accomplish (representing processes or threads). Each task involves preparing a different dish, and each dish has several steps. • Without multithreading (single-threaded model): • You, as the chef, start preparing one dish at a time. While waiting for one dish to cook, you are idle and cannot work on another dish. • The kitchen is not efficiently utilized, and the overall cooking time is longer because each dish must be completed before starting the next. 26
  • 27. 27 With multithreading (multithreaded model): •You decide to use multiple cutting boards and cooking stations to work on multiple dishes simultaneously. •While one dish is simmering on the stove, you are chopping vegetables for another dish or preparing ingredients for a third dish. •This allows you to make progress on multiple tasks concurrently, making better use of your time and the kitchen resources. •As one dish is completed, you can move on to the next without waiting for the others to finish.
  • 28. 28 In this analogy: Each dish is analogous to a thread or process. The chef represents the operating system. The kitchen resources (cutting boards, cooking stations) represent the CPU and other system resources. Multithreading in the operating system works similarly. Multiple threads or processes can execute concurrently, allowing for better resource utilization and improved overall system performance. Each thread can perform a specific task independently, and the operating system manages their execution, scheduling them to run on the available CPU cores efficiently.
  • 29. ADVANTAGES OF MULTITHREADING OPERATING SYSTEM • Resource sharing: Because threads can share any process memory and resources, every program can perform several tasks inside the same address space. • Multiple Processor Architecture: Different threads can execute in parallel on many processors, allowing for high processor usage and efficiency. • Reduced Context Switching Time: As with Thread Context Switching, the threads reduce context switching time while keeping the virtual memory space the same. • Cost-effective: Allocating memory and resources throughout the process generation process has a cost. Context-switch threads are more affordable to construct since they can distribute process resources. 29
  • 30. DISADVANTAGES OF MULTITHREADING OPERATING SYSTEM 1. Complexity and Synchronization • Multithreading introduces complexity into program design and implementation. Coordinating and synchronizing threads to avoid race conditions, deadlocks, and other concurrency-related issues can be challenging. • Debugging multithreaded programs can be more difficult due to the non-deterministic nature of thread execution. 2. Race Conditions • Race conditions occur when multiple threads access shared data concurrently without proper synchronization, leading to unpredictable and erroneous behavior. • Ensuring data consistency and avoiding race conditions requires careful use of synchronization mechanisms like locks and semaphores. 30
  • 31. 31 3. Deadlocks: •A deadlock is a situation where two or more threads are unable to proceed because each is waiting for the other to release a resource. Deadlocks can lead to a complete system halt. •Designing systems to avoid deadlocks requires a good understanding of resource allocation and proper use of synchronization. 4. Thread Starvation and Priority Inversion: •Thread starvation occurs when a thread is unable to access resources or CPU time, potentially leading to poor performance. •Priority inversion occurs when a low-priority thread holds a resource needed by a high-priority thread, leading to the inversion of execution priorities.