Differences between Multi-threading Models

Question

1. Many-to-One Model
2. One-to-One Model
3. Many-to-Many Model

Advantages and disadvantages of each model ?

Can you give an example ?

EDIT:

One thing is confusing me with the Many-to-One Model I'm quoting the book:

"Thread management is done by the thread library in user space, so it is efficient; but the entire process will block if a thread makes a blocking system call. Also, because only one thread can access the kernel at a time, multiple threads are unable to run in parallel on multiprocessors"

Does it mean all processes in kernel will be blocked, due to the fact that the swapping is done by the application, not by OS scheduler. (since in this model we manage threads in user-mode) ? Or, only the threads belonging to the same process of the thread that made the blocking system call will be blocked ?

Thanks in advance!

Answer 1

We have to assign user level threads to kernel level threads, based on the this the mapping can be:

1. One to one (One user thread mapped to one kernel level thread)

2. Many to one(Many User level threads mapped to one kernel level thread)

3. Many to many(Many User level threads mapped to many kernel level threads)

Here the number of kernel level threads are generally set to lesser than number of user level thread, since management of kernel level threads is much more expensive since it involves kernel intervention in their(kernel level thread's) management.

Because of this reason only the fourth mapping of "one to many"(one user level thread to multiple kernel level threads) to one does not make sense.

"Thread management is done by the thread library in user space, so it is efficient; but the entire process will block if a thread makes a blocking system call. Also, because only one thread can access the kernel at a time, multiple threads are unable to run in parallel on multiprocessors"

this example may help to understand this line:

Does it mean all processes in kernel will be blocked, due to the fact that the swapping is done by the application, not by OS scheduler. (since in this model we manage threads in user-mode) ? Or, only the threads belonging to the same process of the thread that made the blocking system call will be blocked ?

One process's threads are independent of other process's threads.So only the threads belonging to the same process of the thread that made the blocking system call will be blocked.

I hope this does make sense to you...