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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/signal-hook-registry-1.4.1/src/lib.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>lib.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../normalize.css"><link rel="stylesheet" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../ayu.css" disabled><link rel="stylesheet" href="../../dark.css" disabled><link rel="stylesheet" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script defer src="../../source-script.js"></script><script defer src="../../source-files.js"></script><script defer src="../../main.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../signal_hook_registry/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../signal_hook_registry/index.html"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span>
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</pre><pre class="rust"><code><span class="attribute">#![doc(test(attr(deny(warnings))))]
#![warn(missing_docs)]
#![allow(unknown_lints, renamed_and_remove_lints, bare_trait_objects)]
</span><span class="doccomment">//! Backend of the [signal-hook] crate.
//!
//! The [signal-hook] crate tries to provide an API to the unix signals, which are a global
//! resource. Therefore, it is desirable an application contains just one version of the crate
//! which manages this global resource. But that makes it impossible to make breaking changes in
//! the API.
//!
//! Therefore, this crate provides very minimal and low level API to the signals that is unlikely
//! to have to change, while there may be multiple versions of the [signal-hook] that all use this
//! low-level API to provide different versions of the high level APIs.
//!
//! It is also possible some other crates might want to build a completely different API. This
//! split allows these crates to still reuse the same low-level routines in this crate instead of
//! going to the (much more dangerous) unix calls.
//!
//! # What this crate provides
//!
//! The only thing this crate does is multiplexing the signals. An application or library can add
//! or remove callbacks and have multiple callbacks for the same signal.
//!
//! It handles dispatching the callbacks and managing them in a way that uses only the
//! [async-signal-safe] functions inside the signal handler. Note that the callbacks are still run
//! inside the signal handler, so it is up to the caller to ensure they are also
//! [async-signal-safe].
//!
//! # What this is for
//!
//! This is a building block for other libraries creating reasonable abstractions on top of
//! signals. The [signal-hook] is the generally preferred way if you need to handle signals in your
//! application and provides several safe patterns of doing so.
//!
//! # Rust version compatibility
//!
//! Currently builds on 1.26.0 an newer and this is very unlikely to change. However, tests
//! require dependencies that don&#39;t build there, so tests need newer Rust version (they are run on
//! stable).
//!
//! # Portability
//!
//! This crate includes a limited support for Windows, based on `signal`/`raise` in the CRT.
//! There are differences in both API and behavior:
//!
//! - Due to lack of `siginfo_t`, we don&#39;t provide `register_sigaction` or `register_unchecked`.
//! - Due to lack of signal blocking, there&#39;s a race condition.
//! After the call to `signal`, there&#39;s a moment where we miss a signal.
//! That means when you register a handler, there may be a signal which invokes
//! neither the default handler or the handler you register.
//! - Handlers registered by `signal` in Windows are cleared on first signal.
//! To match behavior in other platforms, we re-register the handler each time the handler is
//! called, but there&#39;s a moment where we miss a handler.
//! That means when you receive two signals in a row, there may be a signal which invokes
//! the default handler, nevertheless you certainly have registered the handler.
//!
//! [signal-hook]: https://docs.rs/signal-hook
//! [async-signal-safe]: http://www.man7.org/linux/man-pages/man7/signal-safety.7.html
</span><span class="kw">extern crate </span>libc;
<span class="kw">mod </span>half_lock;
<span class="kw">use </span>std::collections::hash_map::Entry;
<span class="kw">use </span>std::collections::{BTreeMap, HashMap};
<span class="kw">use </span>std::io::Error;
<span class="kw">use </span>std::mem;
<span class="attribute">#[cfg(not(windows))]
</span><span class="kw">use </span>std::ptr;
<span class="comment">// Once::new is now a const-fn. But it is not stable in all the rustc versions we want to support
// yet.
</span><span class="attribute">#[allow(deprecated)]
</span><span class="kw">use </span>std::sync::ONCE_INIT;
<span class="kw">use </span>std::sync::{Arc, Once};
<span class="attribute">#[cfg(not(windows))]
</span><span class="kw">use </span>libc::{c_int, c_void, sigaction, siginfo_t};
<span class="attribute">#[cfg(windows)]
</span><span class="kw">use </span>libc::{c_int, sighandler_t};
<span class="attribute">#[cfg(not(windows))]
</span><span class="kw">use </span>libc::{SIGFPE, SIGILL, SIGKILL, SIGSEGV, SIGSTOP};
<span class="attribute">#[cfg(windows)]
</span><span class="kw">use </span>libc::{SIGFPE, SIGILL, SIGSEGV};
<span class="kw">use </span>half_lock::HalfLock;
<span class="comment">// These constants are not defined in the current version of libc, but it actually
// exists in Windows CRT.
</span><span class="attribute">#[cfg(windows)]
</span><span class="kw">const </span>SIG_DFL: sighandler_t = <span class="number">0</span>;
<span class="attribute">#[cfg(windows)]
</span><span class="kw">const </span>SIG_IGN: sighandler_t = <span class="number">1</span>;
<span class="attribute">#[cfg(windows)]
</span><span class="kw">const </span>SIG_GET: sighandler_t = <span class="number">2</span>;
<span class="attribute">#[cfg(windows)]
</span><span class="kw">const </span>SIG_ERR: sighandler_t = !<span class="number">0</span>;
<span class="comment">// To simplify implementation. Not to be exposed.
</span><span class="attribute">#[cfg(windows)]
#[allow(non_camel_case_types)]
</span><span class="kw">struct </span>siginfo_t;
<span class="comment">// # Internal workings
//
// This uses a form of RCU. There&#39;s an atomic pointer to the current action descriptors (in the
// form of IndependentArcSwap, to be able to track what, if any, signal handlers still use the
// version). A signal handler takes a copy of the pointer and calls all the relevant actions.
//
// Modifications to that are protected by a mutex, to avoid juggling multiple signal handlers at
// once (eg. not calling sigaction concurrently). This should not be a problem, because modifying
// the signal actions should be initialization only anyway. To avoid all allocations and also
// deallocations inside the signal handler, after replacing the pointer, the modification routine
// needs to busy-wait for the reference count on the old pointer to drop to 1 and take ownership ‒
// that way the one deallocating is the modification routine, outside of the signal handler.
</span><span class="attribute">#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
</span><span class="kw">struct </span>ActionId(u128);
<span class="doccomment">/// An ID of registered action.
///
/// This is returned by all the registration routines and can be used to remove the action later on
/// with a call to [`unregister`].
</span><span class="attribute">#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
</span><span class="kw">pub struct </span>SigId {
signal: c_int,
action: ActionId,
}
<span class="comment">// This should be dyn Fn(...), but we want to support Rust 1.26.0 and that one doesn&#39;t allow dyn
// yet.
</span><span class="attribute">#[allow(unknown_lints, bare_trait_objects)]
</span><span class="kw">type </span>Action = Fn(<span class="kw-2">&amp;</span>siginfo_t) + Send + Sync;
<span class="attribute">#[derive(Clone)]
</span><span class="kw">struct </span>Slot {
prev: Prev,
<span class="comment">// We use BTreeMap here, because we want to run the actions in the order they were inserted.
// This works, because the ActionIds are assigned in an increasing order.
</span>actions: BTreeMap&lt;ActionId, Arc&lt;Action&gt;&gt;,
}
<span class="kw">impl </span>Slot {
<span class="attribute">#[cfg(windows)]
</span><span class="kw">fn </span>new(signal: libc::c_int) -&gt; <span class="prelude-ty">Result</span>&lt;<span class="self">Self</span>, Error&gt; {
<span class="kw">let </span>old = <span class="kw">unsafe </span>{ libc::signal(signal, handler <span class="kw">as </span>sighandler_t) };
<span class="kw">if </span>old == SIG_ERR {
<span class="kw">return </span><span class="prelude-val">Err</span>(Error::last_os_error());
}
<span class="prelude-val">Ok</span>(Slot {
prev: Prev { signal, info: old },
actions: BTreeMap::new(),
})
}
<span class="attribute">#[cfg(not(windows))]
</span><span class="kw">fn </span>new(signal: libc::c_int) -&gt; <span class="prelude-ty">Result</span>&lt;<span class="self">Self</span>, Error&gt; {
<span class="comment">// C data structure, expected to be zeroed out.
</span><span class="kw">let </span><span class="kw-2">mut </span>new: libc::sigaction = <span class="kw">unsafe </span>{ mem::zeroed() };
<span class="attribute">#[cfg(not(target_os = <span class="string">&quot;aix&quot;</span>))]
</span>{ new.sa_sigaction = handler <span class="kw">as </span>usize; }
<span class="attribute">#[cfg(target_os = <span class="string">&quot;aix&quot;</span>)]
</span>{ new.sa_union.__su_sigaction = handler; }
<span class="comment">// Android is broken and uses different int types than the rest (and different depending on
// the pointer width). This converts the flags to the proper type no matter what it is on
// the given platform.
</span><span class="kw">let </span>flags = libc::SA_RESTART;
<span class="attribute">#[allow(unused_assignments)]
</span><span class="kw">let </span><span class="kw-2">mut </span>siginfo = flags;
siginfo = libc::SA_SIGINFO <span class="kw">as _</span>;
<span class="kw">let </span>flags = flags | siginfo;
new.sa_flags = flags <span class="kw">as _</span>;
<span class="comment">// C data structure, expected to be zeroed out.
</span><span class="kw">let </span><span class="kw-2">mut </span>old: libc::sigaction = <span class="kw">unsafe </span>{ mem::zeroed() };
<span class="comment">// FFI ‒ pointers are valid, it doesn&#39;t take ownership.
</span><span class="kw">if unsafe </span>{ libc::sigaction(signal, <span class="kw-2">&amp;</span>new, <span class="kw-2">&amp;mut </span>old) } != <span class="number">0 </span>{
<span class="kw">return </span><span class="prelude-val">Err</span>(Error::last_os_error());
}
<span class="prelude-val">Ok</span>(Slot {
prev: Prev { signal, info: old },
actions: BTreeMap::new(),
})
}
}
<span class="attribute">#[derive(Clone)]
</span><span class="kw">struct </span>SignalData {
signals: HashMap&lt;c_int, Slot&gt;,
next_id: u128,
}
<span class="attribute">#[derive(Clone)]
</span><span class="kw">struct </span>Prev {
signal: c_int,
<span class="attribute">#[cfg(windows)]
</span>info: sighandler_t,
<span class="attribute">#[cfg(not(windows))]
</span>info: sigaction,
}
<span class="kw">impl </span>Prev {
<span class="attribute">#[cfg(windows)]
</span><span class="kw">fn </span>detect(signal: c_int) -&gt; <span class="prelude-ty">Result</span>&lt;<span class="self">Self</span>, Error&gt; {
<span class="kw">let </span>old = <span class="kw">unsafe </span>{ libc::signal(signal, SIG_GET) };
<span class="kw">if </span>old == SIG_ERR {
<span class="kw">return </span><span class="prelude-val">Err</span>(Error::last_os_error());
}
<span class="prelude-val">Ok</span>(Prev { signal, info: old })
}
<span class="attribute">#[cfg(not(windows))]
</span><span class="kw">fn </span>detect(signal: c_int) -&gt; <span class="prelude-ty">Result</span>&lt;<span class="self">Self</span>, Error&gt; {
<span class="comment">// C data structure, expected to be zeroed out.
</span><span class="kw">let </span><span class="kw-2">mut </span>old: libc::sigaction = <span class="kw">unsafe </span>{ mem::zeroed() };
<span class="comment">// FFI ‒ pointers are valid, it doesn&#39;t take ownership.
</span><span class="kw">if unsafe </span>{ libc::sigaction(signal, ptr::null(), <span class="kw-2">&amp;mut </span>old) } != <span class="number">0 </span>{
<span class="kw">return </span><span class="prelude-val">Err</span>(Error::last_os_error());
}
<span class="prelude-val">Ok</span>(Prev { signal, info: old })
}
<span class="attribute">#[cfg(windows)]
</span><span class="kw">fn </span>execute(<span class="kw-2">&amp;</span><span class="self">self</span>, sig: c_int) {
<span class="kw">let </span>fptr = <span class="self">self</span>.info;
<span class="kw">if </span>fptr != <span class="number">0 </span>&amp;&amp; fptr != SIG_DFL &amp;&amp; fptr != SIG_IGN {
<span class="comment">// FFI ‒ calling the original signal handler.
</span><span class="kw">unsafe </span>{
<span class="kw">let </span>action = mem::transmute::&lt;usize, <span class="kw">extern </span><span class="string">&quot;C&quot; </span><span class="kw">fn</span>(c_int)&gt;(fptr);
action(sig);
}
}
}
<span class="attribute">#[cfg(not(windows))]
</span><span class="kw">unsafe fn </span>execute(<span class="kw-2">&amp;</span><span class="self">self</span>, sig: c_int, info: <span class="kw-2">*mut </span>siginfo_t, data: <span class="kw-2">*mut </span>c_void) {
<span class="attribute">#[cfg(not(target_os = <span class="string">&quot;aix&quot;</span>))]
</span><span class="kw">let </span>fptr = <span class="self">self</span>.info.sa_sigaction;
<span class="attribute">#[cfg(target_os = <span class="string">&quot;aix&quot;</span>)]
</span><span class="kw">let </span>fptr = <span class="self">self</span>.info.sa_union.__su_sigaction <span class="kw">as </span>usize;
<span class="kw">if </span>fptr != <span class="number">0 </span>&amp;&amp; fptr != libc::SIG_DFL &amp;&amp; fptr != libc::SIG_IGN {
<span class="comment">// Android is broken and uses different int types than the rest (and different
// depending on the pointer width). This converts the flags to the proper type no
// matter what it is on the given platform.
//
// The trick is to create the same-typed variable as the sa_flags first and then
// set it to the proper value (does Rust have a way to copy a type in a different
// way?)
</span><span class="attribute">#[allow(unused_assignments)]
</span><span class="kw">let </span><span class="kw-2">mut </span>siginfo = <span class="self">self</span>.info.sa_flags;
siginfo = libc::SA_SIGINFO <span class="kw">as _</span>;
<span class="kw">if </span><span class="self">self</span>.info.sa_flags &amp; siginfo == <span class="number">0 </span>{
<span class="kw">let </span>action = mem::transmute::&lt;usize, <span class="kw">extern </span><span class="string">&quot;C&quot; </span><span class="kw">fn</span>(c_int)&gt;(fptr);
action(sig);
} <span class="kw">else </span>{
<span class="kw">type </span>SigAction = <span class="kw">extern </span><span class="string">&quot;C&quot; </span><span class="kw">fn</span>(c_int, <span class="kw-2">*mut </span>siginfo_t, <span class="kw-2">*mut </span>c_void);
<span class="kw">let </span>action = mem::transmute::&lt;usize, SigAction&gt;(fptr);
action(sig, info, data);
}
}
}
}
<span class="doccomment">/// Lazy-initiated data structure with our global variables.
///
/// Used inside a structure to cut down on boilerplate code to lazy-initialize stuff. We don&#39;t dare
/// use anything fancy like lazy-static or once-cell, since we are not sure they are
/// async-signal-safe in their access. Our code uses the [Once], but only on the write end outside
/// of signal handler. The handler assumes it has already been initialized.
</span><span class="kw">struct </span>GlobalData {
<span class="doccomment">/// The data structure describing what needs to be run for each signal.
</span>data: HalfLock&lt;SignalData&gt;,
<span class="doccomment">/// A fallback to fight/minimize a race condition during signal initialization.
///
/// See the comment inside [`register_unchecked_impl`].
</span>race_fallback: HalfLock&lt;<span class="prelude-ty">Option</span>&lt;Prev&gt;&gt;,
}
<span class="kw">static </span><span class="kw-2">mut </span>GLOBAL_DATA: <span class="prelude-ty">Option</span>&lt;GlobalData&gt; = <span class="prelude-val">None</span>;
<span class="attribute">#[allow(deprecated)]
</span><span class="kw">static </span>GLOBAL_INIT: Once = ONCE_INIT;
<span class="kw">impl </span>GlobalData {
<span class="kw">fn </span>get() -&gt; <span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span><span class="self">Self </span>{
<span class="kw">unsafe </span>{ GLOBAL_DATA.as_ref().unwrap() }
}
<span class="kw">fn </span>ensure() -&gt; <span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span><span class="self">Self </span>{
GLOBAL_INIT.call_once(|| <span class="kw">unsafe </span>{
GLOBAL_DATA = <span class="prelude-val">Some</span>(GlobalData {
data: HalfLock::new(SignalData {
signals: HashMap::new(),
next_id: <span class="number">1</span>,
}),
race_fallback: HalfLock::new(<span class="prelude-val">None</span>),
});
});
<span class="self">Self</span>::get()
}
}
<span class="attribute">#[cfg(windows)]
</span><span class="kw">extern </span><span class="string">&quot;C&quot; </span><span class="kw">fn </span>handler(sig: c_int) {
<span class="kw">if </span>sig != SIGFPE {
<span class="comment">// Windows CRT `signal` resets handler every time, unless for SIGFPE.
// Reregister the handler to retain maximal compatibility.
// Problems:
// - It&#39;s racy. But this is inevitably racy in Windows.
// - Interacts poorly with handlers outside signal-hook-registry.
</span><span class="kw">let </span>old = <span class="kw">unsafe </span>{ libc::signal(sig, handler <span class="kw">as </span>sighandler_t) };
<span class="kw">if </span>old == SIG_ERR {
<span class="comment">// MSDN doesn&#39;t describe which errors might occur,
// but we can tell from the Linux manpage that
// EINVAL (invalid signal number) is mostly the only case.
// Therefore, this branch must not occur.
// In any case we can do nothing useful in the signal handler,
// so we&#39;re going to abort silently.
</span><span class="kw">unsafe </span>{
libc::abort();
}
}
}
<span class="kw">let </span>globals = GlobalData::get();
<span class="kw">let </span>fallback = globals.race_fallback.read();
<span class="kw">let </span>sigdata = globals.data.read();
<span class="kw">if let </span><span class="prelude-val">Some</span>(<span class="kw-2">ref </span>slot) = sigdata.signals.get(<span class="kw-2">&amp;</span>sig) {
slot.prev.execute(sig);
<span class="kw">for </span>action <span class="kw">in </span>slot.actions.values() {
action(<span class="kw-2">&amp;</span>siginfo_t);
}
} <span class="kw">else if let </span><span class="prelude-val">Some</span>(prev) = fallback.as_ref() {
<span class="comment">// In case we get called but don&#39;t have the slot for this signal set up yet, we are under
// the race condition. We may have the old signal handler stored in the fallback
// temporarily.
</span><span class="kw">if </span>sig == prev.signal {
prev.execute(sig);
}
<span class="comment">// else -&gt; probably should not happen, but races with other threads are possible so
// better safe
</span>}
}
<span class="attribute">#[cfg(not(windows))]
</span><span class="kw">extern </span><span class="string">&quot;C&quot; </span><span class="kw">fn </span>handler(sig: c_int, info: <span class="kw-2">*mut </span>siginfo_t, data: <span class="kw-2">*mut </span>c_void) {
<span class="kw">let </span>globals = GlobalData::get();
<span class="kw">let </span>fallback = globals.race_fallback.read();
<span class="kw">let </span>sigdata = globals.data.read();
<span class="kw">if let </span><span class="prelude-val">Some</span>(slot) = sigdata.signals.get(<span class="kw-2">&amp;</span>sig) {
<span class="kw">unsafe </span>{ slot.prev.execute(sig, info, data) };
<span class="kw">let </span>info = <span class="kw">unsafe </span>{ info.as_ref() };
<span class="kw">let </span>info = info.unwrap_or_else(|| {
<span class="comment">// The info being null seems to be illegal according to POSIX, but has been observed on
// some probably broken platform. We can&#39;t do anything about that, that is just broken,
// but we are not allowed to panic in a signal handler, so we are left only with simply
// aborting. We try to write a message what happens, but using the libc stuff
// (`eprintln` is not guaranteed to be async-signal-safe).
</span><span class="kw">unsafe </span>{
<span class="kw">const </span>MSG: <span class="kw-2">&amp;</span>[u8] =
<span class="string">b&quot;Platform broken, got NULL as siginfo to signal handler. Aborting&quot;</span>;
libc::write(<span class="number">2</span>, MSG.as_ptr() <span class="kw">as </span><span class="kw-2">*const </span><span class="kw">_</span>, MSG.len());
libc::abort();
}
});
<span class="kw">for </span>action <span class="kw">in </span>slot.actions.values() {
action(info);
}
} <span class="kw">else if let </span><span class="prelude-val">Some</span>(prev) = fallback.as_ref() {
<span class="comment">// In case we get called but don&#39;t have the slot for this signal set up yet, we are under
// the race condition. We may have the old signal handler stored in the fallback
// temporarily.
</span><span class="kw">if </span>prev.signal == sig {
<span class="kw">unsafe </span>{ prev.execute(sig, info, data) };
}
<span class="comment">// else -&gt; probably should not happen, but races with other threads are possible so
// better safe
</span>}
}
<span class="doccomment">/// List of forbidden signals.
///
/// Some signals are impossible to replace according to POSIX and some are so special that this
/// library refuses to handle them (eg. SIGSEGV). The routines panic in case registering one of
/// these signals is attempted.
///
/// See [`register`].
</span><span class="kw">pub const </span>FORBIDDEN: <span class="kw-2">&amp;</span>[c_int] = FORBIDDEN_IMPL;
<span class="attribute">#[cfg(windows)]
</span><span class="kw">const </span>FORBIDDEN_IMPL: <span class="kw-2">&amp;</span>[c_int] = <span class="kw-2">&amp;</span>[SIGILL, SIGFPE, SIGSEGV];
<span class="attribute">#[cfg(not(windows))]
</span><span class="kw">const </span>FORBIDDEN_IMPL: <span class="kw-2">&amp;</span>[c_int] = <span class="kw-2">&amp;</span>[SIGKILL, SIGSTOP, SIGILL, SIGFPE, SIGSEGV];
<span class="doccomment">/// Registers an arbitrary action for the given signal.
///
/// This makes sure there&#39;s a signal handler for the given signal. It then adds the action to the
/// ones called each time the signal is delivered. If multiple actions are set for the same signal,
/// all are called, in the order of registration.
///
/// If there was a previous signal handler for the given signal, it is chained ‒ it will be called
/// as part of this library&#39;s signal handler, before any actions set through this function.
///
/// On success, the function returns an ID that can be used to remove the action again with
/// [`unregister`].
///
/// # Panics
///
/// If the signal is one of (see [`FORBIDDEN`]):
///
/// * `SIGKILL`
/// * `SIGSTOP`
/// * `SIGILL`
/// * `SIGFPE`
/// * `SIGSEGV`
///
/// The first two are not possible to override (and the underlying C functions simply ignore all
/// requests to do so, which smells of possible bugs, or return errors). The rest can be set, but
/// generally needs very special handling to do so correctly (direct manipulation of the
/// application&#39;s address space, `longjmp` and similar). Unless you know very well what you&#39;re
/// doing, you&#39;ll shoot yourself into the foot and this library won&#39;t help you with that.
///
/// # Errors
///
/// Since the library manipulates signals using the low-level C functions, all these can return
/// errors. Generally, the errors mean something like the specified signal does not exist on the
/// given platform ‒ after a program is debugged and tested on a given OS, it should never return
/// an error.
///
/// However, if an error *is* returned, there are no guarantees if the given action was registered
/// or not.
///
/// # Safety
///
/// This function is unsafe, because the `action` is run inside a signal handler. The set of
/// functions allowed to be called from within is very limited (they are called async-signal-safe
/// functions by POSIX). These specifically do *not* contain mutexes and memory
/// allocation/deallocation. They *do* contain routines to terminate the program, to further
/// manipulate signals (by the low-level functions, not by this library) and to read and write file
/// descriptors. Calling program&#39;s own functions consisting only of these is OK, as is manipulating
/// program&#39;s variables ‒ however, as the action can be called on any thread that does not have the
/// given signal masked (by default no signal is masked on any thread), and mutexes are a no-go,
/// this is harder than it looks like at first.
///
/// As panicking from within a signal handler would be a panic across FFI boundary (which is
/// undefined behavior), the passed handler must not panic.
///
/// If you find these limitations hard to satisfy, choose from the helper functions in the
/// [signal-hook](https://docs.rs/signal-hook) crate ‒ these provide safe interface to use some
/// common signal handling patters.
///
/// # Race condition
///
/// Upon registering the first hook for a given signal into this library, there&#39;s a short race
/// condition under the following circumstances:
///
/// * The program already has a signal handler installed for this particular signal (through some
/// other library, possibly).
/// * Concurrently, some other thread installs a different signal handler while it is being
/// installed by this library.
/// * At the same time, the signal is delivered.
///
/// Under such conditions signal-hook might wrongly &quot;chain&quot; to the older signal handler for a short
/// while (until the registration is fully complete).
///
/// Note that the exact conditions of the race condition might change in future versions of the
/// library. The recommended way to avoid it is to register signals before starting any additional
/// threads, or at least not to register signals concurrently.
///
/// Alternatively, make sure all signals are handled through this library.
///
/// # Performance
///
/// Even when it is possible to repeatedly install and remove actions during the lifetime of a
/// program, the installation and removal is considered a slow operation and should not be done
/// very often. Also, there&#39;s limited (though huge) amount of distinct IDs (they are `u128`).
///
/// # Examples
///
/// ```rust
/// extern crate signal_hook_registry;
///
/// use std::io::Error;
/// use std::process;
///
/// fn main() -&gt; Result&lt;(), Error&gt; {
/// let signal = unsafe {
/// signal_hook_registry::register(signal_hook::consts::SIGTERM, || process::abort())
/// }?;
/// // Stuff here...
/// signal_hook_registry::unregister(signal); // Not really necessary.
/// Ok(())
/// }
/// ```
</span><span class="kw">pub unsafe fn </span>register&lt;F&gt;(signal: c_int, action: F) -&gt; <span class="prelude-ty">Result</span>&lt;SigId, Error&gt;
<span class="kw">where
</span>F: Fn() + Sync + Send + <span class="lifetime">&#39;static</span>,
{
register_sigaction_impl(signal, <span class="kw">move </span>|<span class="kw">_</span>: <span class="kw-2">&amp;</span><span class="kw">_</span>| action())
}
<span class="doccomment">/// Register a signal action.
///
/// This acts in the same way as [`register`], including the drawbacks, panics and performance
/// characteristics. The only difference is the provided action accepts a [`siginfo_t`] argument,
/// providing information about the received signal.
///
/// # Safety
///
/// See the details of [`register`].
</span><span class="attribute">#[cfg(not(windows))]
</span><span class="kw">pub unsafe fn </span>register_sigaction&lt;F&gt;(signal: c_int, action: F) -&gt; <span class="prelude-ty">Result</span>&lt;SigId, Error&gt;
<span class="kw">where
</span>F: Fn(<span class="kw-2">&amp;</span>siginfo_t) + Sync + Send + <span class="lifetime">&#39;static</span>,
{
register_sigaction_impl(signal, action)
}
<span class="kw">unsafe fn </span>register_sigaction_impl&lt;F&gt;(signal: c_int, action: F) -&gt; <span class="prelude-ty">Result</span>&lt;SigId, Error&gt;
<span class="kw">where
</span>F: Fn(<span class="kw-2">&amp;</span>siginfo_t) + Sync + Send + <span class="lifetime">&#39;static</span>,
{
<span class="macro">assert!</span>(
!FORBIDDEN.contains(<span class="kw-2">&amp;</span>signal),
<span class="string">&quot;Attempted to register forbidden signal {}&quot;</span>,
signal,
);
register_unchecked_impl(signal, action)
}
<span class="doccomment">/// Register a signal action without checking for forbidden signals.
///
/// This acts in the same way as [`register_unchecked`], including the drawbacks, panics and
/// performance characteristics. The only difference is the provided action doesn&#39;t accept a
/// [`siginfo_t`] argument.
///
/// # Safety
///
/// See the details of [`register`].
</span><span class="kw">pub unsafe fn </span>register_signal_unchecked&lt;F&gt;(signal: c_int, action: F) -&gt; <span class="prelude-ty">Result</span>&lt;SigId, Error&gt;
<span class="kw">where
</span>F: Fn() + Sync + Send + <span class="lifetime">&#39;static</span>,
{
register_unchecked_impl(signal, <span class="kw">move </span>|<span class="kw">_</span>: <span class="kw-2">&amp;</span><span class="kw">_</span>| action())
}
<span class="doccomment">/// Register a signal action without checking for forbidden signals.
///
/// This acts the same way as [`register_sigaction`], but without checking for the [`FORBIDDEN`]
/// signals. All the signals passed are registered and it is up to the caller to make some sense of
/// them.
///
/// Note that you really need to know what you&#39;re doing if you change eg. the `SIGSEGV` signal
/// handler. Generally, you don&#39;t want to do that. But unlike the other functions here, this
/// function still allows you to do it.
///
/// # Safety
///
/// See the details of [`register`].
</span><span class="attribute">#[cfg(not(windows))]
</span><span class="kw">pub unsafe fn </span>register_unchecked&lt;F&gt;(signal: c_int, action: F) -&gt; <span class="prelude-ty">Result</span>&lt;SigId, Error&gt;
<span class="kw">where
</span>F: Fn(<span class="kw-2">&amp;</span>siginfo_t) + Sync + Send + <span class="lifetime">&#39;static</span>,
{
register_unchecked_impl(signal, action)
}
<span class="kw">unsafe fn </span>register_unchecked_impl&lt;F&gt;(signal: c_int, action: F) -&gt; <span class="prelude-ty">Result</span>&lt;SigId, Error&gt;
<span class="kw">where
</span>F: Fn(<span class="kw-2">&amp;</span>siginfo_t) + Sync + Send + <span class="lifetime">&#39;static</span>,
{
<span class="kw">let </span>globals = GlobalData::ensure();
<span class="kw">let </span>action = Arc::from(action);
<span class="kw">let </span><span class="kw-2">mut </span>lock = globals.data.write();
<span class="kw">let </span><span class="kw-2">mut </span>sigdata = SignalData::clone(<span class="kw-2">&amp;</span>lock);
<span class="kw">let </span>id = ActionId(sigdata.next_id);
sigdata.next_id += <span class="number">1</span>;
<span class="kw">match </span>sigdata.signals.entry(signal) {
Entry::Occupied(<span class="kw-2">mut </span>occupied) =&gt; {
<span class="macro">assert!</span>(occupied.get_mut().actions.insert(id, action).is_none());
}
Entry::Vacant(place) =&gt; {
<span class="comment">// While the sigaction/signal exchanges the old one atomically, we are not able to
// atomically store it somewhere a signal handler could read it. That poses a race
// condition where we could lose some signals delivered in between changing it and
// storing it.
//
// Therefore we first store the old one in the fallback storage. The fallback only
// covers the cases where the slot is not yet active and becomes &quot;inert&quot; after that,
// even if not removed (it may get overwritten by some other signal, but for that the
// mutex in globals.data must be unlocked here - and by that time we already stored the
// slot.
//
// And yes, this still leaves a short race condition when some other thread could
// replace the signal handler and we would be calling the outdated one for a short
// time, until we install the slot.
</span>globals
.race_fallback
.write()
.store(<span class="prelude-val">Some</span>(Prev::detect(signal)<span class="question-mark">?</span>));
<span class="kw">let </span><span class="kw-2">mut </span>slot = Slot::new(signal)<span class="question-mark">?</span>;
slot.actions.insert(id, action);
place.insert(slot);
}
}
lock.store(sigdata);
<span class="prelude-val">Ok</span>(SigId { signal, action: id })
}
<span class="doccomment">/// Removes a previously installed action.
///
/// This function does nothing if the action was already removed. It returns true if it was removed
/// and false if the action wasn&#39;t found.
///
/// It can unregister all the actions installed by [`register`] as well as the ones from downstream
/// crates (like [`signal-hook`](https://docs.rs/signal-hook)).
///
/// # Warning
///
/// This does *not* currently return the default/previous signal handler if the last action for a
/// signal was just unregistered. That means that if you replaced for example `SIGTERM` and then
/// removed the action, the program will effectively ignore `SIGTERM` signals from now on, not
/// terminate on them as is the default action. This is OK if you remove it as part of a shutdown,
/// but it is not recommended to remove termination actions during the normal runtime of
/// application (unless the desired effect is to create something that can be terminated only by
/// SIGKILL).
</span><span class="kw">pub fn </span>unregister(id: SigId) -&gt; bool {
<span class="kw">let </span>globals = GlobalData::ensure();
<span class="kw">let </span><span class="kw-2">mut </span>replace = <span class="bool-val">false</span>;
<span class="kw">let </span><span class="kw-2">mut </span>lock = globals.data.write();
<span class="kw">let </span><span class="kw-2">mut </span>sigdata = SignalData::clone(<span class="kw-2">&amp;</span>lock);
<span class="kw">if let </span><span class="prelude-val">Some</span>(slot) = sigdata.signals.get_mut(<span class="kw-2">&amp;</span>id.signal) {
replace = slot.actions.remove(<span class="kw-2">&amp;</span>id.action).is_some();
}
<span class="kw">if </span>replace {
lock.store(sigdata);
}
replace
}
<span class="comment">// We keep this one here for strict backwards compatibility, but the API is kind of bad. One can
// delete actions that don&#39;t belong to them, which is kind of against the whole idea of not
// breaking stuff for others.
</span><span class="attribute">#[deprecated(
since = <span class="string">&quot;1.3.0&quot;</span>,
note = <span class="string">&quot;Don&#39;t use. Can influence unrelated parts of program / unknown actions&quot;
</span>)]
#[doc(hidden)]
</span><span class="kw">pub fn </span>unregister_signal(signal: c_int) -&gt; bool {
<span class="kw">let </span>globals = GlobalData::ensure();
<span class="kw">let </span><span class="kw-2">mut </span>replace = <span class="bool-val">false</span>;
<span class="kw">let </span><span class="kw-2">mut </span>lock = globals.data.write();
<span class="kw">let </span><span class="kw-2">mut </span>sigdata = SignalData::clone(<span class="kw-2">&amp;</span>lock);
<span class="kw">if let </span><span class="prelude-val">Some</span>(slot) = sigdata.signals.get_mut(<span class="kw-2">&amp;</span>signal) {
<span class="kw">if </span>!slot.actions.is_empty() {
slot.actions.clear();
replace = <span class="bool-val">true</span>;
}
}
<span class="kw">if </span>replace {
lock.store(sigdata);
}
replace
}
<span class="attribute">#[cfg(test)]
</span><span class="kw">mod </span>tests {
<span class="kw">use </span>std::sync::atomic::{AtomicUsize, Ordering};
<span class="kw">use </span>std::sync::Arc;
<span class="kw">use </span>std::thread;
<span class="kw">use </span>std::time::Duration;
<span class="attribute">#[cfg(not(windows))]
</span><span class="kw">use </span>libc::{pid_t, SIGUSR1, SIGUSR2};
<span class="attribute">#[cfg(windows)]
</span><span class="kw">use </span>libc::SIGTERM <span class="kw">as </span>SIGUSR1;
<span class="attribute">#[cfg(windows)]
</span><span class="kw">use </span>libc::SIGTERM <span class="kw">as </span>SIGUSR2;
<span class="kw">use super</span>::<span class="kw-2">*</span>;
<span class="attribute">#[test]
#[should_panic]
</span><span class="kw">fn </span>panic_forbidden() {
<span class="kw">let _ </span>= <span class="kw">unsafe </span>{ register(SIGILL, || ()) };
}
<span class="doccomment">/// Registering the forbidden signals is allowed in the _unchecked version.
</span><span class="attribute">#[test]
#[allow(clippy::redundant_closure)] </span><span class="comment">// Clippy, you&#39;re wrong. Because it changes the return value.
</span><span class="kw">fn </span>forbidden_raw() {
<span class="kw">unsafe </span>{ register_signal_unchecked(SIGFPE, || std::process::abort()).unwrap() };
}
<span class="attribute">#[test]
</span><span class="kw">fn </span>signal_without_pid() {
<span class="kw">let </span>status = Arc::new(AtomicUsize::new(<span class="number">0</span>));
<span class="kw">let </span>action = {
<span class="kw">let </span>status = Arc::clone(<span class="kw-2">&amp;</span>status);
<span class="kw">move </span>|| {
status.store(<span class="number">1</span>, Ordering::Relaxed);
}
};
<span class="kw">unsafe </span>{
register(SIGUSR2, action).unwrap();
libc::raise(SIGUSR2);
}
<span class="kw">for _ in </span><span class="number">0</span>..<span class="number">10 </span>{
thread::sleep(Duration::from_millis(<span class="number">100</span>));
<span class="kw">let </span>current = status.load(Ordering::Relaxed);
<span class="kw">match </span>current {
<span class="comment">// Not yet
</span><span class="number">0 </span>=&gt; <span class="kw">continue</span>,
<span class="comment">// Good, we are done with the correct result
</span><span class="kw">_ if </span>current == <span class="number">1 </span>=&gt; <span class="kw">return</span>,
<span class="kw">_ </span>=&gt; <span class="macro">panic!</span>(<span class="string">&quot;Wrong result value {}&quot;</span>, current),
}
}
<span class="macro">panic!</span>(<span class="string">&quot;Timed out waiting for the signal&quot;</span>);
}
<span class="attribute">#[test]
#[cfg(not(windows))]
</span><span class="kw">fn </span>signal_with_pid() {
<span class="kw">let </span>status = Arc::new(AtomicUsize::new(<span class="number">0</span>));
<span class="kw">let </span>action = {
<span class="kw">let </span>status = Arc::clone(<span class="kw-2">&amp;</span>status);
<span class="kw">move </span>|siginfo: <span class="kw-2">&amp;</span>siginfo_t| {
<span class="comment">// Hack: currently, libc exposes only the first 3 fields of siginfo_t. The pid
// comes somewhat later on. Therefore, we do a Really Ugly Hack and define our
// own structure (and hope it is correct on all platforms). But hey, this is
// only the tests, so we are going to get away with this.
</span><span class="attribute">#[repr(C)]
</span><span class="kw">struct </span>SigInfo {
_fields: [c_int; <span class="number">3</span>],
<span class="attribute">#[cfg(all(target_pointer_width = <span class="string">&quot;64&quot;</span>, target_os = <span class="string">&quot;linux&quot;</span>))]
</span>_pad: c_int,
pid: pid_t,
}
<span class="kw">let </span>s: <span class="kw-2">&amp;</span>SigInfo = <span class="kw">unsafe </span>{
(siginfo <span class="kw">as </span><span class="kw-2">*const </span><span class="kw">_ as </span>usize <span class="kw">as </span><span class="kw-2">*const </span>SigInfo)
.as_ref()
.unwrap()
};
status.store(s.pid <span class="kw">as </span>usize, Ordering::Relaxed);
}
};
<span class="kw">let </span>pid;
<span class="kw">unsafe </span>{
pid = libc::getpid();
register_sigaction(SIGUSR2, action).unwrap();
libc::raise(SIGUSR2);
}
<span class="kw">for _ in </span><span class="number">0</span>..<span class="number">10 </span>{
thread::sleep(Duration::from_millis(<span class="number">100</span>));
<span class="kw">let </span>current = status.load(Ordering::Relaxed);
<span class="kw">match </span>current {
<span class="comment">// Not yet (PID == 0 doesn&#39;t happen)
</span><span class="number">0 </span>=&gt; <span class="kw">continue</span>,
<span class="comment">// Good, we are done with the correct result
</span><span class="kw">_ if </span>current == pid <span class="kw">as </span>usize =&gt; <span class="kw">return</span>,
<span class="kw">_ </span>=&gt; <span class="macro">panic!</span>(<span class="string">&quot;Wrong status value {}&quot;</span>, current),
}
}
<span class="macro">panic!</span>(<span class="string">&quot;Timed out waiting for the signal&quot;</span>);
}
<span class="doccomment">/// Check that registration works as expected and that unregister tells if it did or not.
</span><span class="attribute">#[test]
</span><span class="kw">fn </span>register_unregister() {
<span class="kw">let </span>signal = <span class="kw">unsafe </span>{ register(SIGUSR1, || ()).unwrap() };
<span class="comment">// It was there now, so we can unregister
</span><span class="macro">assert!</span>(unregister(signal));
<span class="comment">// The next time unregistering does nothing and tells us so.
</span><span class="macro">assert!</span>(!unregister(signal));
}
}
</code></pre></div>
</section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="signal_hook_registry" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html>