Project ForgeWhich one or more of the following standard C library functions will ALWAYS invoke a system call when executed from a single-threaded process in a UNIX/Linux operating system?
(A) exit (B) malloc (C) sleep (D) strlen
- exit
- Bmalloc
- sleep
- Dstrlen
Explanation
strlen is pure user-space computation — never a syscall. malloc is often satisfied from an already-obtained heap region without needing to ask the kernel for more memory (brk/mmap) — not guaranteed every call. sleep() always requires the kernel's scheduler/timer to suspend the calling process for a duration — there is no way to implement this purely in user space, so it's guaranteed. exit() performs user-space cleanup (flushing buffers, atexit handlers) but ALWAYS eventually calls the underlying _exit() system call to actually terminate the process — a process can never terminate itself without kernel involvement, so this is also guaranteed.
Source: GATE CS 2021 (Session 1 / Set-1) (2021)
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