UCONTEXT(3)

UCONTEXT(3) — user thread context 💅

okay so this is the Library Functions Manual page for UCONTEXT(3), aka ucontext — user thread context. yes bestie, we’re talking about the little struct that holds a whole user thread’s vibe. slay.

---

🌸 NAME 🌸

ucontext — user thread context. that’s the whole name section, periodt.

📚 LIBRARY 📚

Standard C Library (libc, -lc). it’s giving “link me and let’s go.” 🫶

✨ SYNOPSIS ✨

#include <ucontext.h>

🦋 DESCRIPTION 🦋

The ucontext_t type is a structure type suitable for holding the context for a user thread of execution. A thread’s context includes its stack, saved registers, and list of blocked signals. literally the whole little survival kit for a thread. 💖

The ucontext_t structure contains at least these fields — yes, at least, don’t come for me:

• ucontext_t *uc_link — context to assume when this one returns
• sigset_t uc_sigmask — signals being blocked
• stack_t uc_stack — stack area
• mcontext_t uc_mcontext — saved registers

The uc_link field points to the context to resume when this context’s entry point function returns. so if your main character entry point function dips, uc_link is the next context waiting to take over. If uc_link is equal to NULL, then the process exits when this context returns. no next context, no party, process says bye. 😭

The uc_mcontext field is machine-dependent and should be treated as opaque by portable applications. translation: do not peer into it like it’s a group chat screenshot; portable apps treat it as opaque. respect the mystery. 🙈

The following functions are defined to manipulate ucontext_t structures — these are the little icons that actually do the work:

int getcontext(ucontext_t *);
ucontext_t * getcontextx(void);
int setcontext(const ucontext_t *);
void makecontext(ucontext_t *, void (*)(void), int, ...);
int swapcontext(ucontext_t *, const ucontext_t *);

👀 SEE ALSO 👀

go read these next, bestie — they’re literally right there:

• sigaltstack(2)
• getcontext(3)
• getcontextx(3)
• makecontext(3)

⭐ STANDARDS ⭐

The ucontext_t type conforms to X/Open System Interfaces and Headers Issue 5 (“XSH5”) and IEEE Std 1003.1-2001 (“POSIX.1”). so yes, it has receipts. ✨

The IEEE Std 1003.1-2008 (“POSIX.1”) revision removed the ucontext_t from the specification. that’s the spec revision tea, periodt.

---

xoxo, Debian — March 23, 2020 💖