Single vs Multithreaded process

Single vs Multithreaded process

• Code – Contains instruction
• Data – holds global variable
• Files – opening and closing files
• Register – contain information about CPU state
• Stack – parameters, local varibles, functions

Types of Threads

• User Threads
• Thread creation, scheduling, management are done by a thread library at the user level
• If a user thread performs a system call which blocks it, all the other threads in that process are also automatically blocked, whole process is blocked
• Advantages
• Thread switching does not require kernel mode privileges
• User level threads can run on any operating system
• User level threads are fast to create and manage
• Is generic and can run on any Os
• Disadvantages
• In a typical operating system, most system calls are blocking
• Multithreaded application cannot take advantage of multiprocessing

Types of Threads cont...

• Kernel threads
• Are created, scheduled, managed by the kernel.
• If one thread in a process is blocked, the process need not be blocked.
• Advantages
• Kernel can simultaneously schedule multiple threads from the same process on multiple processes.
• If one thread in a process is blocked, the Kernel can schedule another thread of the same process.
• Kernel routines can be multithreaded
• Disadvantages
• Kernel threads are generally slower to create and manage than the user threads.
• Is specific to the operating system

Multithreading models

• Categories of threading implementation
• One to One
• One of the earliest implementation of true multithreading
• One user thread to one kernel thread
• Each user user-level thread created by the application is known to the kernel and all threads can access the kernel at the same time.
• Disadvantage of this model is that creating user thread requires the corresponding Kernel thread.
• OS/2, windows NT and windows 2000 use one to one model