Threads

Last updated Nov 8, 2022 Edit Source

A thread (or lightweight process) consists of its own thread id, program counter, registers and stack space. However it shares the same data and code as the parent process.

Multithreading: A process can have multiple threads: this allows efficient sharing of memory for the program without having to create additional processes which has high overhead. This is because thread creation is primarily done via APIs and not system calls. ^7d353c

Want to support an arbitrary number of threads but the OS can only support a limited number due to physical constraints

Logical (user) threads: Created in user space and allows users to create as many threads as they want Kernel threads (physical): Created in kernel space and slower to create and manage than user threads; Resources are eventually allocated in kernel threads

Ways to map logical to physical:

• Many to one: can result in blockage of thread when one is in use
• One to one: creating user threads = creating kernel threads; not very efficient
• Many to many: not easy to decide an efficient mapping

Explain the difference between a single-threaded and a multi-threaded process.

• Threads in a process share code, data and heap regions of memory, whereas stack space is unique to each thread. Also, each thread has its own Thread Control Block (TCB), similar to a PCB.
• In a single-threaded process, there is only one thread of execution, and hence it is identical to a process.
• In a multi-threaded process, the individual threads can execute concurrently, thus increasing system throughput; when one thread of a process is blocked (“waiting” state), another thread can continue its execution (“running” state).