GATE CS 2014 Set 1 Q20 — Processes and Threads

To determine which statement is FALSE, let us analyze each option:

• Option A: User-level threads are not scheduled by the kernel.
  True. The operating system kernel is unaware of user-level threads. They are managed and scheduled entirely by a user-space thread library.
• Option B: When a user-level thread is blocked, all other threads of its process are blocked.
  True. Since the kernel only sees the single process containing these threads, any blocking system call made by one user-level thread causes the kernel to block the entire process.
• Option C: Context switching between user-level threads is faster than context switching between kernel-level threads.
  True. Switching between user-level threads does not require a transition to kernel mode (no system call or trap), which avoids the overhead of mode switching and saving/restoring kernel registers.
• Option D: Kernel-level threads cannot share the code segment.
  False. By definition, all threads of a single process (whether user-level or kernel-level) share the same address space. This shared address space includes the code segment, data segment, and operating system resources (like open files). Therefore, kernel-level threads of the same process can and do share the code segment.

Since the question asks for the FALSE statement, the correct option is D.