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•No special support needed from the kernel (use any Unix)
•Thread creation and context switch are fast (no syscall)
•Defines its own thread model and scheduling policies
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What are the advantages and disadvantages of user level threads and kernel level threads?
- USER LEVEL THREADS Aadvantages: · User-level threads can be implemented on operating system that does not support threads. · Implementing user-level threads does not require modification of operating system where everything is managed by the thread library · Simple representation which the thread is represented by a the thread ID, program counter, register, stack , all stored in user process address space · Simple management where creating new threads, switching threads and synchronization between threads can be done without intervention of the kernel · Fast and efficient where switching thread is much more inexpensive compared to a system call - Disadvantages: · There is a lack of coordination between threads and operating system kernel. A process gets one time slice no matter it has 1 thread or 10000 threads within it. It is up to the thread itself to give up the control to other threads · If one thread made a blocking system call, the entire process can be blocked in the kernel, even if other threads in the same process are in the ready state KERNEL LEVEL THREAD: - Advantages: · Because kernel has the full knowledge of all the threads, scheduler may decide to allocate more time to a process having large number of threads than process having small number of thread, where the kernel threads come useful for intense application - Disadvantages: · Kernel level threads are slow and inefficient, since kernel must manage and schedule all the threads as well as the processes. It requires a full TCB for each thread to maintain information about threads, which results in increasing of overheads and kernel complexity
How do threads work in an operating system?
threads are the light weight process or it is a part of the process which can execute simulteniously by sharing systm resources.... two types of thread 1.user level thread 2.kernel level thread
Describe the action taken by a kernel to context switch between kernel level threads?
Context switching between kernel threads typically requires saving the value of the CPU registers from the thread being switched out and restoring the CPU registers of the new thread being scheduled.
What are kernel level threads?
KERNEL In computing, the kernel is the central component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources (the communication between hardware and software components).
What resources are shared by all threads of a process?
The resources that are shared by all threads of a process in Operating SystemsareMain memoryInput Output DevicesInput Output ChannelsFiles
Is user level threads are transparent to kernel level threads?
user level theads are not tranparent to kernel level threads.
Example for user level threads and kernel level threads?
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Are posix threads user level or kernel level?
POSIX threads are user level threads, because had a interface library and the operating systems don't control his ejecution and does not know
What are the circumstances of user level thread better than kernel level thread?
There are two distinct models of thread controls, and they are user-level threads and kernel-level threads. The thread function library to implement user-level threads usually runs on top of the system in user mode. Thus, these threads within a process are invisible to the operating system. User-level threads have extremely low overhead, and can achieve high performance in computation. However, using the blocking system calls like read(), the entire process would block. Also, the scheduling control by the thread runtime system may cause some threads to gain exclusive access to the CPU and prevent other threads from obtaining the CPU. Finally, access to multiple processors is not guaranteed since the operating system is not aware of existence of these types of threads. On the other hand, kernel-level threads will guarantee multiple processor access but the computing performance is lower than user-level threads due to load on the system. The synchronization and sharing resources among threads are still less expensive than multiple-process model, but more expensive than user-level threads. Thus, user-level thread is better than kernel level thread.
Is there one stack per process when user level threads are used?
In both kernel and User level they have one stack per thread
What are the advantages and disadvantages of user level threads and kernel level threads?
- USER LEVEL THREADS Aadvantages: · User-level threads can be implemented on operating system that does not support threads. · Implementing user-level threads does not require modification of operating system where everything is managed by the thread library · Simple representation which the thread is represented by a the thread ID, program counter, register, stack , all stored in user process address space · Simple management where creating new threads, switching threads and synchronization between threads can be done without intervention of the kernel · Fast and efficient where switching thread is much more inexpensive compared to a system call - Disadvantages: · There is a lack of coordination between threads and operating system kernel. A process gets one time slice no matter it has 1 thread or 10000 threads within it. It is up to the thread itself to give up the control to other threads · If one thread made a blocking system call, the entire process can be blocked in the kernel, even if other threads in the same process are in the ready state KERNEL LEVEL THREAD: - Advantages: · Because kernel has the full knowledge of all the threads, scheduler may decide to allocate more time to a process having large number of threads than process having small number of thread, where the kernel threads come useful for intense application - Disadvantages: · Kernel level threads are slow and inefficient, since kernel must manage and schedule all the threads as well as the processes. It requires a full TCB for each thread to maintain information about threads, which results in increasing of overheads and kernel complexity
What takes longer a context switch with user level threads or one with kernel level threads?
Kernel level threads take a longer time to context switch since OS will have to save and reload each and every TCB (Thread Control block) where as in user level no kernel intervention threads simply context switch more efficiently. But there are disadvantages such as since OS sees the user leve threads as a whole process it will not give a large portion of CPU time for execution if a thread is blocked the whole process goes to the waiting state please correct my answer if im wrong godlovesu49@hotmail.com thanks regards yo
Can a multithread solution using multiple user level threads achieve better performance on a multiprocessor system than on a single processor system?
A multithreaded system comprising of multiple user-levelthreads cannot make use of the different processors in a multiprocessorsystem simultaneously. The operating system sees only a single processand will not schedule the different threads of the process on separateprocessors. Consequently, there is no performance benefit associatedwith executing multiple user-level threads on a multiprocessor system.
What is the difference between Kernel and User level thread?
A kernel thread, sometimes called a LWP (Lightweight Process) is created and scheduled by the kernel. Kernel threads are often more expensive to create than user threads and the system calls to directly create kernel threads are very platform specific. A user thread is normally created by a threading library and scheduling is managed by the threading library itself (Which runs in user mode). All user threads belong to process that created them. The advantage of user threads is that they are portable. The major difference can be seen when using multiprocessor systems, user threads completely managed by the threading library can't be ran in parallel on the different CPUs, although this means they will run fine on uniprocessor systems. Since kernel threads use the kernel scheduler, different kernel threads can run on different CPUs. Many systems implement threading differently, A many-to-one threading model maps many user processes directly to one kernel thread, the kernel thread can be thought of as the main process. A one-to-one threading model maps each user thread directly to one kernel thread, this model allows parallel processing on the multiprocessor systems. Each kernel thread can be thought of as a VP (Virtual Process) which is managed by the scheduler.
Different kind of threads in MFC?
There are two main kinds of threads implementations: User-space threads and Kernel-supported threads. Mikaela
How do threads work in an operating system?
threads are the light weight process or it is a part of the process which can execute simulteniously by sharing systm resources.... two types of thread 1.user level thread 2.kernel level thread
Describe the action taken by a thread library to context switch between user level threads?
AnswerThe thread library function performs the following actions to context switch between user level threads:1. Copy all live registers to Thread control Block (TCB)2. Restore the state of the thread to run next i.e. (copy the values of live registers from (TCB) to registers)3. Move to the next thread to execute
