1 #![doc( 2 test(attr(deny(warnings))), 3 test(attr(allow(bare_trait_objects, unknown_lints))) 4 )] 5 #![allow( 6 unknown_lints, 7 renamed_and_removed_lints, 8 intra_doc_link_resolution_failure, 9 broken_itra_doc_links 10 )] 11 //! Library for easier and safe Unix signal handling 12 //! 13 //! Unix signals are inherently hard to handle correctly, for several reasons: 14 //! 15 //! * They are a global resource. If a library wants to set its own signal handlers, it risks 16 //! disturbing some other library. It is possible to chain the previous signal handler, but then 17 //! it is impossible to remove the old signal handlers from the chains in any practical manner. 18 //! * They can be called from whatever thread, requiring synchronization. Also, as they can 19 //! interrupt a thread at any time, making most handling race-prone. 20 //! * According to the POSIX standard, the set of functions one may call inside a signal handler is 21 //! limited to very few of them. To highlight, mutexes (or other locking mechanisms) and memory 22 //! allocation and deallocation is *not* allowed. 23 //! 24 //! This library aims to solve some of the problems. It provides a global registry of actions 25 //! performed on arrival of signals. It is possible to register multiple actions for the same 26 //! signal and it is possible to remove the actions later on. If there was a previous signal 27 //! handler when the first action for a signal is registered, it is chained (but the original one 28 //! can't be removed). 29 //! 30 //! The main function of the library is [`register`](fn.register.html). 31 //! 32 //! It also offers several common actions one might want to register, implemented in the correct 33 //! way. They are scattered through submodules and have the same limitations and characteristics as 34 //! the [`register`](fn.register.html) function. Generally, they work to postpone the action taken 35 //! outside of the signal handler, where the full freedom and power of rust is available. 36 //! 37 //! Unlike other Rust libraries for signal handling, this should be flexible enough to handle all 38 //! the common and useful patterns. 39 //! 40 //! The library avoids all the newer fancy signal-handling routines. These generally have two 41 //! downsides: 42 //! 43 //! * They are not fully portable, therefore the library would have to contain *both* the 44 //! implementation using the basic routines and the fancy ones. As signal handling is not on the 45 //! hot path of most programs, this would not bring any actual benefit. 46 //! * The other routines require that the given signal is masked in all application's threads. As 47 //! the signals are not masked by default and a new thread inherits the signal mask of its 48 //! parent, it is possible to guarantee such global mask by masking them before any threads 49 //! start. While this is possible for an application developer to do, it is not possible for a 50 //! a library. 51 //! 52 //! # Warning 53 //! 54 //! Even with this library, you should thread with care. It does not eliminate all the problems 55 //! mentioned above. 56 //! 57 //! Also, note that the OS may collate multiple instances of the same signal into just one call of 58 //! the signal handler. Furthermore, some abstractions implemented here also naturally collate 59 //! multiple instances of the same signal. The general guarantee is, if there was at least one 60 //! signal of the given number delivered, an action will be taken, but it is not specified how many 61 //! times ‒ signals work mostly as kind of „wake up now“ nudge, if the application is slow to wake 62 //! up, it may be nudged multiple times before it does so. 63 //! 64 //! # Signal limitations 65 //! 66 //! OS limits still apply ‒ it is not possible to redefine certain signals (eg. `SIGKILL` or 67 //! `SIGSTOP`) and it is probably a *very* stupid idea to touch certain other ones (`SIGSEGV`, 68 //! `SIGFPE`, `SIGILL`). Therefore, this library will panic if any attempt at manipulating these is 69 //! made. There are some use cases for redefining the latter ones, but these are not well served by 70 //! this library and you really *really* have to know what you're doing and are generally on your 71 //! own doing that. 72 //! 73 //! # Signal masks 74 //! 75 //! As the library uses `sigaction` under the hood, signal masking works as expected (eg. with 76 //! `pthread_sigmask`). This means, signals will *not* be delivered if the signal is masked in all 77 //! program's threads. 78 //! 79 //! By the way, if you do want to modify the signal mask (or do other Unix-specific magic), the 80 //! [nix](https://crates.io/crates/nix) crate offers safe interface to many low-level functions, 81 //! including 82 //! [`pthread_sigmask`](https://docs.rs/nix/0.11.0/nix/sys/signal/fn.pthread_sigmask.html). 83 //! 84 //! # Portability 85 //! 86 //! It should work on any POSIX.1-2001 system, which are all the major big OSes with the notable 87 //! exception of Windows. 88 //! 89 //! Non-standard signals are also supported. Pass the signal value directly from `libc` or use 90 //! the numeric value directly. 91 //! 92 //! ```rust 93 //! use std::sync::Arc; 94 //! use std::sync::atomic::{AtomicBool}; 95 //! let term = Arc::new(AtomicBool::new(false)); 96 //! let _ = signal_hook::flag::register(libc::SIGINT, Arc::clone(&term)); 97 //! ``` 98 //! 99 //! This crate includes a limited support for Windows, based on `signal`/`raise` in the CRT. 100 //! There are differences in both API and behavior: 101 //! 102 //! - `iterator` and `pipe` are not yet implemented. 103 //! - We have only a few signals: `SIGABRT`, `SIGABRT_COMPAT`, `SIGBREAK`, 104 //! `SIGFPE`, `SIGILL`, `SIGINT`, `SIGSEGV` and `SIGTERM`. 105 //! - Due to lack of signal blocking, there's a race condition. 106 //! After the call to `signal`, there's a moment where we miss a signal. 107 //! That means when you register a handler, there may be a signal which invokes 108 //! neither the default handler or the handler you register. 109 //! - Handlers registered by `signal` in Windows are cleared on first signal. 110 //! To match behavior in other platforms, we re-register the handler each time the handler is 111 //! called, but there's a moment where we miss a handler. 112 //! That means when you receive two signals in a row, there may be a signal which invokes 113 //! the default handler, nevertheless you certainly have registered the handler. 114 //! 115 //! Moreover, signals won't work as you expected. `SIGTERM` isn't actually used and 116 //! not all `Ctrl-C`s are turned into `SIGINT`. 117 //! 118 //! Patches to improve Windows support in this library are welcome. 119 //! 120 //! # Examples 121 //! 122 //! ```rust 123 //! extern crate signal_hook; 124 //! 125 //! use std::io::Error; 126 //! use std::sync::Arc; 127 //! use std::sync::atomic::{AtomicBool, Ordering}; 128 //! 129 //! fn main() -> Result<(), Error> { 130 //! let term = Arc::new(AtomicBool::new(false)); 131 //! signal_hook::flag::register(signal_hook::SIGTERM, Arc::clone(&term))?; 132 //! while !term.load(Ordering::Relaxed) { 133 //! // Do some time-limited stuff here 134 //! // (if this could block forever, then there's no guarantee the signal will have any 135 //! // effect). 136 //! # 137 //! # // Hack to terminate the example, not part of the real code. 138 //! # term.store(true, Ordering::Relaxed); 139 //! } 140 //! Ok(()) 141 //! } 142 //! ``` 143 //! 144 //! # Features 145 //! 146 //! * `mio-support`: The [`Signals` iterator](iterator/struct.Signals.html) becomes pluggable into 147 //! mio 0.6. 148 //! * `mio-0_7-support`: The [`Signals` iterator](iterator/struct.Signals.html) becomes pluggable into 149 //! mio 0.7. 150 //! * `tokio-support`: The [`Signals`](iterator/struct.Signals.html) can be turned into 151 //! [`Async`](iterator/struct.Async.html), which provides a `Stream` interface for integration in 152 //! the asynchronous world. 153 154 #[cfg(feature = "tokio-support")] 155 extern crate futures; 156 extern crate libc; 157 #[cfg(feature = "mio-support")] 158 extern crate mio; 159 #[cfg(any(test, feature = "mio-0_7-support"))] 160 extern crate mio_0_7; 161 extern crate signal_hook_registry; 162 #[cfg(feature = "tokio-support")] 163 extern crate tokio_reactor; 164 165 pub mod cleanup; 166 pub mod flag; 167 #[cfg(not(windows))] 168 pub mod iterator; 169 #[cfg(not(windows))] 170 pub mod pipe; 171 172 #[cfg(not(windows))] 173 pub use libc::{ 174 SIGABRT, SIGALRM, SIGBUS, SIGCHLD, SIGCONT, SIGFPE, SIGHUP, SIGILL, SIGINT, SIGIO, SIGKILL, 175 SIGPIPE, SIGPROF, SIGQUIT, SIGSEGV, SIGSTOP, SIGSYS, SIGTERM, SIGTRAP, SIGUSR1, SIGUSR2, 176 SIGWINCH, 177 }; 178 179 #[cfg(windows)] 180 pub use libc::{SIGABRT, SIGFPE, SIGILL, SIGINT, SIGSEGV, SIGTERM}; 181 182 // NOTE: they perhaps deserve backport to libc. 183 #[cfg(windows)] 184 /// Same as `SIGABRT`, but the number is compatible to other platforms. 185 pub const SIGABRT_COMPAT: libc::c_int = 6; 186 #[cfg(windows)] 187 /// Ctrl-Break is pressed for Windows Console processes. 188 pub const SIGBREAK: libc::c_int = 21; 189 190 pub use signal_hook_registry::{register, unregister, SigId, FORBIDDEN}; 191