Process Management in OS Flashcards
1
Q
Process
A
A program in execution: A process is essentially a program in the midst of execution. Processes are the active content within a computer system, starting from when the program is opened (or executed) until it is closed.
2
Q
Batch System
A
Processes are referred to as “jobs.” This terminology is reminiscent of older computing systems where tasks were submitted in batches.
3
Q
Time-shared systems
A
Processes are often referred to as “user programs” or “tasks.” This reflects the multi-user, multitasking nature of such systems where multiple processes may be executed concurrently.
4
Q
Items of a process
A
- Program counter: Holds the address of the next instruction to be executed, thus guiding the sequential flow of control.
- Stack: Used for storing temporary data like function parameters, return addresses, and local variables.
- Data section: Contains the global and static variables used by the program.
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Q
Process State
A
- New: The process is being created.
- Running: The process is currently executing instructions.
- Waiting: The process is paused, waiting for an event to occur.
- Ready: The process is ready to run and waiting for processor allocation.
- Terminated: The process has completed execution and is exiting.
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Q
Process Control Block
A
- Process State: The current status of the process (e.g., New, Running, Waiting, Ready, Terminated).
- Program Counter: Holds the address of the next instruction for the process to execute.
- CPU Registers: Contains the process’s current register values when it is not running.
- CPU Scheduling Information: Includes priority information and other data necessary for scheduling the process.
- Memory-Management Information: Details about the process’s allocated memory, including base and limit registers.
- Accounting Information: Information tracking the use of processor time and other resources by the process.
- I/O Status Information: Lists the I/O devices allocated to the process and a list of open files.
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Q
Process Scheduling Queues
A
- Job Queue: The set of all processes in the system.
- Ready Queue: The set of all processes residing in main memory that are ready and waiting to execute.
- Device Queues: Sets of processes waiting for an I/O device.
8
Q
Short-term scheduler
A
- Selects which process to execute next and allocates CPU.
- Invoked very frequently to maintain efficient processor use.
9
Q
Long-term scheduler
A
- Selects processes to bring into the ready queue.
- Controls the degree of multiprogramming.
- Balances the mix of CPU-bound and I/O-bound processes.
10
Q
Process Creation
A
- Parent Process Creates Children: Parent processes can create child processes, forming a tree of processes.
- Resource Sharing: Determines how resources are shared between parent and child processes.
- Execution: Parent and children can either execute concurrently or the parent can wait for the children to terminate.
- Address Space:
The child process starts as a duplicate of the parent (same program and data). The child can load a new program into its address space. - UNIX System Calls: fork to create a new process, exec to load a new program into the process’s address space.
11
Q
Process termination - exit
A
- The process completes its execution and asks the OS to delete it.
- The parent process can receive output data from the child through the wait system call.
- The operating system deallocates the resources of the process.
12
Q
Process Termination - abort
A
- The child has exceeded its allocated resources.
- The task assigned to the child is no longer required.
- The parent is exiting, and the OS does not allow the child to continue independently.
13
Q
Advantages of Process Cooperation
A
- Information sharing
- Computation speed-up
- Modularity
- Convenience
14
Q
Direct Communicaton
A
- Links are established automatically.
- A link is associated with exactly one pair of processes.
- Between each pair, there exists exactly one link.
- Links are usually bi-directional, though they can be unidirectional.
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Q
Indirect Communication
A
- A link is established only if processes share a common mailbox.
- A link can be associated with many processes.
- Each pair of processes can share several links.
- Links can be unidirectional or bi-directional.
16
Q
Blocking (Synchronous) Message Passing
A
The sending/receiving processes wait until the other side is ready.
17
Q
Non-blocking (Asynchronous) Message Passing
A
The sending/receiving processes do not wait for each other.
18
Q
Buffering - Zero Capacity
A
No messages are buffered; direct handoff.
19
Q
Buffering - Bounded Capcacity
A
A fixed number of messages can be buffered.
20
Q
Buffering - Unbounded Capacity
A
An unlimited number of messages can be buffered.
21
Q
Sockets
A
Endpoints for communication, identified by an IP address and a port number (e.g., 161.25.19.8:1625).
22
Q
Remote Procedure Calls (RPCs)
A
Enable procedure calls between distributed processes, with structured messages and stubs acting as client-side and server-side proxies.
23
Q
Remote Method Invocation (RMI)
A
A Java mechanism similar to RPCs but specifically for Java objects and methods.
24
Q
Ordinary Pipes
A
- Producer/Consumer
- Unidirectional: Prod -> Consumer
- Parent -> Child Process
- Half-Duplex
- Same machine
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Named Pipes
- Bidirectional
- No relationship
- Continue
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Full Duplex
Data can travel in both directions at the same time
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Half Duplex
Data can travel only one way at a time
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Benefits of Threads
- Responsiveness: Enhances system responsiveness by allowing tasks to run concurrently
or in parallel.
- Resource Sharing: Enables efficient sharing of resources among multiple tasks or processes.
- Economy: Improves system economy through task multiplexing and reducing overhead.
- Utilization of MP Architectures: Boosts performance by leveraging multi-processor (MP) architectures for parallel task execution.
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Many-to-One Model
Multiple user-level threads map to one kernel thread.
- Solaris Green Threads: An implementation of threads that maps multiple user- level threads to a single kernel thread.
- GNU Portable Threads: A user-level thread library where multiple threads are managed by a single process without kernel-level context switching.
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One-to-One Model
Each user-level thread maps to a kernel thread.
- Windows NT/XP/2000: Each user-level thread corresponds to a single kernel thread, allowing better concurrency on multiprocessor systems.
- Linux: Implements a one-to-one threading model where each user thread is associated with a distinct kernel thread.
- Solaris 9 and later: Shifted to a one-to-one model to improve performance and scalability on multiprocessor systems.
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Many-to-Many Model
- Solaris prior to version 9: Allowed mapping many user-level threads to many kernel threads, providing flexibility in how threads were managed.
- Windows NT/2000 with the ThreadFiber package: Provided the ability to use a many-to-many threading model through additional libraries, offering a hybrid approach between user and kernel threads.
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Two-level Model
- IRIX
- HU-UX
- Tru-64 UNIX Solaris-8 and earlier
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Threading issues
- System Calls: Interactions with fork() and exec() can affect threads differently. Thread - Cancellation: Terminating a thread before it has completed.
- Signal Handling: Managing UNIX signals within multithreaded applications. Thread
- Pools: Using a pool of pre-created threads to handle tasks.
- Thread-Specific Data: Allowing individual threads to have their own copies of data.
- Scheduler Activations: Communication between the kernel and thread library to manage kernel threads.
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Thread-Pools
- Concept: Create a number of threads in a pool to wait for and perform work.
- Advantages: Slight performance improvement and the ability to limit the number of concurrent threads in an application.
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Signal Handling
- To the thread that caused the signal.
- To every thread in the process.
- To specific threads in the process.
- To a designated thread handling all signals for the process.
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Thread Cancellation
- Asynchronous Cancellation: Terminates the target thread immediately.
- Deferred Cancellation: The thread periodically checks if it should terminate, allowing for a safer cleanup.
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Thread-Specific Data
Allows each thread to maintain its own set of data, beneficial when the thread creation process is outside the programmer's control.
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