1. Responsiveness (needn’t to wait for a lengthy process)
2. Resources sharing
3. Economy (Context switching between threads is easy)
4. Utilization of multiprocessor architectures (perfect utilization of the multiple processors).
1. User thread
2. Kernel thread
User threads are easy to create and use but the disadvantage is that if they perform a blocking system calls the kernel is engaged completely to the single user thread blocking other processes. They are created in user space.Kernel threads are supported directly by the operating system. They are slower to create and manage. Most of the OS like Windows NT, Windows 2000, Solaris2, BeOS, and Tru64 Unix support kernel threading.
Java threads are created and managed by the java virtual machine, they do not easily fall under the category of either user or kernel thread.
Many OS provide both kernel threading and user threading. They are called multithreading models. They are of three types:
1. Many-to-one model (many user level thread and one kernel thread).
2. One-to-one model
3. Many-to –many
In the first model only one user can access the kernel thread by not allowing multi-processing. Example: Green threads of Solaris.The second model allows multiple threads to run on parallel processing systems. Creating user thread needs to create corresponding kernel thread (disadvantage).Example: Windows NT, Windows 2000, OS/2.The third model allows the user to create as many threads as necessary and the corresponding kernel threads can run in parallel on a multiprocessor.
Example: Solaris2, IRIX, HP-UX, and Tru64 Unix.
P-thread refers to the POSIX standard (IEEE 1003.1c) defining an API for thread creation and synchronization. This is a specification for thread behavior, not an implementation. The windows OS have generally not supported the P-threads.