shoney.arickathil
c0b0dbb846
- README: shipped concurrency/HTTP/WebSockets sat in the roadmap as "not yet available"; "no package manager" contradicted [deps]; the deps example would not have compiled (the key IS the module name) - runtime/README: leads with wovm, wo-rt.c demoted to a historical section; dropped 2 nonexistent recipes, crates/rt, @gc refcounting, 13 suites -> 18 - employee + log-watcher READMEs claimed "does not compile"; both are gates - error catalog: +10 emitted codes incl WO-E250, the only diagnostic the shipped query surface raises; recorded why the sweep rotted - language-surface: group-by parses, then the typechecker refuses it - 00-code-review + 00-link-audit re-run; history kept, not rewritten - 48 dead Rust-era exploration links de-linked rather than re-pointed (their prose names the retired plan by number); successor map -> discarded.md - 08-project-structure: compiler/plan/ never existed; corpus has 9 dirs, 5 empty - releasing.md: dropped a --draft step the workflow never had - new docs/00-doc-audit.md: findings + disposition, incl one row where the audit was wrong and the doc it accused was right - status folders removed: 34 stories flat, status only in frontmatter; 252 links recomputed from resolved paths; board/board-views/structure retaught - story 24 -> in-progress, since frontmatter is now the only truth - new iteration 38: fs mutation verbs + net.connect, the two capability families no iteration owned - new iteration 39: gofiber/fiber v3.5.0 parity study. The ledger called CSRF/sessions unblocked by iteration 34's HMAC, but the runtime has no source of randomness at all - linkcheck skips .dev/.superpowers: 0 broken paths, 0 bad anchors Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
77 lines
3.5 KiB
Markdown
77 lines
3.5 KiB
Markdown
# 04 — `signalfd`
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Unix signals as file descriptors. `signalfd(fd, mask)` installs a mask on the process and returns an fd that becomes readable when any masked signal arrives. Replaces signal handlers entirely — no `sigaction`, no re-entrancy minefield, no interrupted syscalls. The whole `wo` binary's shutdown path is one `signalfd` on the event loop.
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## Kernel source
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| Path | What |
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| --- | --- |
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| [`reference/linux/fs/signalfd.c`](../../../../.dev/reference/linux/fs/signalfd.c) | `SYSCALL_DEFINE4(signalfd4, ...)` + `signalfd_dequeue`. |
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| [`reference/linux/include/uapi/linux/signalfd.h`](../../../../.dev/reference/linux/include/uapi/linux/signalfd.h) | `struct signalfd_siginfo`, `SFD_*` flags. |
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| [`reference/linux/kernel/signal.c`](../../../../.dev/reference/linux/kernel/signal.c) | Background: `sigprocmask`, pending-signal dequeue. |
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## Man pages
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`man 2 signalfd`, `man 7 signal`.
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## Rust FFI via `libc`
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```rust
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use libc::{signalfd, signalfd_siginfo, sigset_t};
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use libc::{sigemptyset, sigaddset, sigprocmask};
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use libc::{SFD_CLOEXEC, SFD_NONBLOCK, SIG_BLOCK, SIG_UNBLOCK};
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use libc::{SIGINT, SIGTERM, SIGHUP, SIGQUIT};
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```
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## Direct-syscall example
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```rust
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unsafe {
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// 1. Block the signals in the thread so the kernel delivers them via the fd instead
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let mut mask: sigset_t = std::mem::zeroed();
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libc::sigemptyset(&mut mask);
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libc::sigaddset(&mut mask, libc::SIGINT);
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libc::sigaddset(&mut mask, libc::SIGTERM);
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if libc::sigprocmask(libc::SIG_BLOCK, &mask, std::ptr::null_mut()) < 0 {
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return Err(io::Error::last_os_error());
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}
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// 2. Create the fd
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let fd = libc::signalfd(-1, &mask, libc::SFD_CLOEXEC | libc::SFD_NONBLOCK);
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if fd < 0 { return Err(io::Error::last_os_error()); }
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// 3. Register fd on epoll. On EPOLLIN:
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let mut info: signalfd_siginfo = std::mem::zeroed();
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let n = libc::read(fd, &mut info as *mut _ as *mut _, std::mem::size_of::<signalfd_siginfo>());
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if n as usize == std::mem::size_of::<signalfd_siginfo>() {
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match info.ssi_signo as i32 {
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libc::SIGINT | libc::SIGTERM => begin_graceful_shutdown(),
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_ => {}
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}
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}
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}
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```
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## Key flags
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| Flag | Meaning |
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| --- | --- |
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| `SFD_CLOEXEC` | Close on exec. Always set. |
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| `SFD_NONBLOCK` | Non-blocking reads. Required when on `epoll`. |
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| `SIG_BLOCK` | Passed to `sigprocmask` to add the set to the current mask. The corresponding `SIG_UNBLOCK` / `SIG_SETMASK` are available if you need them. |
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## Gotchas
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- **Blocking the signal with `sigprocmask` is mandatory.** Otherwise the default handler runs and kills the process before the fd ever becomes readable. Block once at boot, never unblock.
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- **Per-thread mask.** `sigprocmask` is per-thread. In a single-threaded runtime that's fine; if you ever spawn threads, use `pthread_sigmask` on each so the main loop gets the signals.
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- **`signalfd_siginfo` is big** (128 bytes). Read into an aligned buffer; partial reads return `EINVAL`.
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- **Doesn't catch `SIGKILL` or `SIGSTOP`.** Nothing does. Those bypass everything.
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- **Child exit notifications (`SIGCHLD`)** work via signalfd but `pidfd` (see [10-pidfd.md](10-pidfd.md)) is usually the better fit for clean child supervision.
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## Used by
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`04-cutover-remove-tokio-axum.md` — replaces `tokio::signal::ctrl_c()` for graceful shutdown. Every subsequent phase inherits this pattern.
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## v1 port source
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[`reference/crates/wo-event/src/signalfd.rs`](../../../../.dev/reference/crates/wo-event/src/signalfd.rs) (62 LOC) — `SignalFd::new(&[SIGINT, SIGTERM]) -> SignalFd` with a safe `read_signo()` helper.
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