Lecture 4 (unfinished) Flashcards
What is Resource Ownership in terms of Processes?
Process includes a virtual address space to hold the process image
• The OS performs a protection function to prevent unwanted interference between processes with respect to resources
What is Scheduling/Execution in terms of Processes?
Follows an execution path that may be interleaved with other processes
A process has an execution state (Running, Ready, etc.) and a dispatching priority, and is the entity that is scheduled and dispatched by the OS
What is a Thread (Lightweight process)?
The unit of dispatching is referred to as a thread
What is a process (task)?
Defined in a multithreaded environment as “the
unit of resource allocation and a unit of protection”
Associated with processes:
A virtual address space that holds the process image
Protected access to:
Processors
Other processes (for interprocess communication)
Files
I/O resources (devices and channels)
What is multithreading?
Multithreading - The ability of an OS to support multiple, concurrent paths of execution within a single process.
Check multithread and single thread model/pics slide 5
Check multithread and single thread model/pics slide 5
What does each thread have ?
Access to the memory and resources of its processes, shared with all other threads in that process
An execution state (Running, Ready, etc.)
A saved thread context when not running
An execution stack
Some per-thread static storage for local variables
2 benefits of threads?
Takes less time to create a new thread than a process
Less time to terminate a thread than a process
What is Thread Use in a Single-User System?
Foreground and background work in parallel
•Asynchronous processing
•Speed of execution
•Modular program structure
What is suspending a process?
Suspending a process involves suspending all threads of the process
What is a termination of a process?
Termination of a process terminates all threads within the process
What is thread syncronization?
It is necessary to synchronize the activities of the various threads
•All threads of a process share the same address space and other resources
•Any alteration of a resource by one thread affects the other threads in the same process
What are the 2 types of threads?
User Level thread
Kernel Level thread
What is a user Level Thread (ULT)?
- All thread management is done by the application
* The kernel is not aware of the existence of threads
2 advantages of ULT?
Thread switching does not require kernel mode privileges
ULTs can run on any OS
1 Disadvantage of ULT?
Many system calls are blocking
When a ULT executes a system call, the thread and all of the threads within the process are blocked
What is a kernel level thread?
Thread management is done by the kernel
No thread management code in the application level, simply an application programming interface (API) to the kernel thread facility
Advantage of kernel level thread?
The kernel can simultaneously schedule multiple threads from the same process on multiple processors
Disadvantage of kernel Level thread?
The transfer of control from one thread to another within the same process requires a mode switch to the kernel
