16 - Threads Flashcards
What are some problems with using processes in operating systems?
Processes have heavyweight PCBs, expensive context switching, separate address spaces, and limited shared memory, resulting in high memory usage and slower performance.
What is a thread, and how does it differ from a process?
A thread is a unit of execution within a process. It shares the process’s memory and resources while having its own program counter, register set, and stack, making it lighter weight than a process.
What are the advantages of using threads over processes?
Threads allow for lower overhead in context switching, efficient resource sharing, and faster execution due to their lightweight nature.
What is the typical overhead of context switching for processes compared to threads in Linux?
Process creation and termination (via fork()/exit()) can take about 250 microseconds, kernel-level thread operations around 90 microseconds, and user-level thread operations approximately 5 microseconds.
What are kernel-level threads (KLTs) and what benefits do they offer?
Kernel-level threads are managed by the operating system’s kernel, supporting true parallelism on multi-core systems and enabling synchronization via OS-level primitives, though they incur moderate overhead.
What are user-level threads (ULTs) and why are they faster?
User-level threads are managed entirely by user-space libraries, avoiding kernel intervention. This results in significantly lower overhead (around 5 microseconds) for creation and management.
How do modern operating systems support multithreading compared to earlier systems like MS-DOS?
Modern operating systems like Windows, Linux, and macOS allow multiple processes to each support multiple threads, whereas earlier systems like MS-DOS supported only a single thread per process.
What role do the program counter, register set, and stack play in a thread?
They define a thread’s execution state: the program counter indicates the next instruction, the register set holds temporary data, and the stack manages function calls and local variables.
How does the Java Runtime Environment (JRE) handle threads?
The JRE supports multithreading by allowing a single process to manage multiple threads concurrently within the same memory space.
What benefits do threads provide in applications such as web servers?
Threads allow web servers to handle multiple concurrent requests efficiently by sharing common data, reducing overhead and improving performance compared to using separate processes.
