src/libstd/panicking.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use prelude::v1::*;
  12 use io::prelude::*;
  13
  14 use any::Any;
  15 use cell::Cell;
  16 use cell::RefCell;
  17 use intrinsics;
  18 use sync::StaticRwLock;
  19 use sync::atomic::{AtomicBool, Ordering};
  20 use sys::stdio::Stderr;
  21 use sys_common::backtrace;
  22 use sys_common::thread_info;
  23 use sys_common::util;
  24 use thread;
  25
  26 thread_local! { pub static PANIC_COUNT: Cell<usize> = Cell::new(0) }
  27
  28 thread_local! {
  29     pub static LOCAL_STDERR: RefCell<Option<Box<Write + Send>>> = {
  30         RefCell::new(None)
  31     }
  32 }
  33
  34 #[derive(Copy, Clone)]
  35 enum Hook {
  36     Default,
  37     Custom(*mut (Fn(&PanicInfo) + 'static + Sync + Send)),
  38 }
  39
  40 static HOOK_LOCK: StaticRwLock = StaticRwLock::new();
  41 static mut HOOK: Hook = Hook::Default;
  42 static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
  43
  44 /// Registers a custom panic hook, replacing any that was previously registered.
  45 ///
  46 /// The panic hook is invoked when a thread panics, but before it begins
  47 /// unwinding the stack. The default hook prints a message to standard error
  48 /// and generates a backtrace if requested, but this behavior can be customized
  49 /// with the `set_hook` and `take_hook` functions.
  50 ///
  51 /// The hook is provided with a `PanicInfo` struct which contains information
  52 /// about the origin of the panic, including the payload passed to `panic!` and
  53 /// the source code location from which the panic originated.
  54 ///
  55 /// The panic hook is a global resource.
  56 ///
  57 /// # Panics
  58 ///
  59 /// Panics if called from a panicking thread.
  60 #[unstable(feature = "panic_handler", reason = "awaiting feedback", issue = "30449")]
  61 pub fn set_hook(hook: Box<Fn(&PanicInfo) + 'static + Sync + Send>) {
  62     if thread::panicking() {
  63         panic!("cannot modify the panic hook from a panicking thread");
  64     }
  65
  66     unsafe {
  67         let lock = HOOK_LOCK.write();
  68         let old_hook = HOOK;
  69         HOOK = Hook::Custom(Box::into_raw(hook));
  70         drop(lock);
  71
  72         if let Hook::Custom(ptr) = old_hook {
  73             Box::from_raw(ptr);
  74         }
  75     }
  76 }
  77
  78 /// Unregisters the current panic hook, returning it.
  79 ///
  80 /// If no custom hook is registered, the default hook will be returned.
  81 ///
  82 /// # Panics
  83 ///
  84 /// Panics if called from a panicking thread.
  85 #[unstable(feature = "panic_handler", reason = "awaiting feedback", issue = "30449")]
  86 pub fn take_hook() -> Box<Fn(&PanicInfo) + 'static + Sync + Send> {
  87     if thread::panicking() {
  88         panic!("cannot modify the panic hook from a panicking thread");
  89     }
  90
  91     unsafe {
  92         let lock = HOOK_LOCK.write();
  93         let hook = HOOK;
  94         HOOK = Hook::Default;
  95         drop(lock);
  96
  97         match hook {
  98             Hook::Default => Box::new(default_hook),
  99             Hook::Custom(ptr) => {Box::from_raw(ptr)} // FIXME #30530
 100         }
 101     }
 102 }
 103
 104 /// A struct providing information about a panic.
 105 #[unstable(feature = "panic_handler", reason = "awaiting feedback", issue = "30449")]
 106 pub struct PanicInfo<'a> {
 107     payload: &'a (Any + Send),
 108     location: Location<'a>,
 109 }
 110
 111 impl<'a> PanicInfo<'a> {
 112     /// Returns the payload associated with the panic.
 113     ///
 114     /// This will commonly, but not always, be a `&'static str` or `String`.
 115     #[unstable(feature = "panic_handler", reason = "awaiting feedback", issue = "30449")]
 116     pub fn payload(&self) -> &(Any + Send) {
 117         self.payload
 118     }
 119
 120     /// Returns information about the location from which the panic originated,
 121     /// if available.
 122     ///
 123     /// This method will currently always return `Some`, but this may change
 124     /// in future versions.
 125     #[unstable(feature = "panic_handler", reason = "awaiting feedback", issue = "30449")]
 126     pub fn location(&self) -> Option<&Location> {
 127         Some(&self.location)
 128     }
 129 }
 130
 131 /// A struct containing information about the location of a panic.
 132 #[unstable(feature = "panic_handler", reason = "awaiting feedback", issue = "30449")]
 133 pub struct Location<'a> {
 134     file: &'a str,
 135     line: u32,
 136 }
 137
 138 impl<'a> Location<'a> {
 139     /// Returns the name of the source file from which the panic originated.
 140     #[unstable(feature = "panic_handler", reason = "awaiting feedback", issue = "30449")]
 141     pub fn file(&self) -> &str {
 142         self.file
 143     }
 144
 145     /// Returns the line number from which the panic originated.
 146     #[unstable(feature = "panic_handler", reason = "awaiting feedback", issue = "30449")]
 147     pub fn line(&self) -> u32 {
 148         self.line
 149     }
 150 }
 151
 152 fn default_hook(info: &PanicInfo) {
 153     let panics = PANIC_COUNT.with(|s| s.get());
 154
 155     // If this is a double panic, make sure that we print a backtrace
 156     // for this panic. Otherwise only print it if logging is enabled.
 157     let log_backtrace = panics >= 2 || backtrace::log_enabled();
 158
 159     let file = info.location.file;
 160     let line = info.location.line;
 161
 162     let msg = match info.payload.downcast_ref::<&'static str>() {
 163         Some(s) => *s,
 164         None => match info.payload.downcast_ref::<String>() {
 165             Some(s) => &s[..],
 166             None => "Box<Any>",
 167         }
 168     };
 169     let mut err = Stderr::new().ok();
 170     let thread = thread_info::current_thread();
 171     let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
 172
 173     let write = |err: &mut ::io::Write| {
 174         let _ = writeln!(err, "thread '{}' panicked at '{}', {}:{}",
 175                          name, msg, file, line);
 176
 177         if log_backtrace {
 178             let _ = backtrace::write(err);
 179         } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
 180             let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` for a backtrace.");
 181         }
 182     };
 183
 184     let prev = LOCAL_STDERR.with(|s| s.borrow_mut().take());
 185     match (prev, err.as_mut()) {
 186         (Some(mut stderr), _) => {
 187             write(&mut *stderr);
 188             let mut s = Some(stderr);
 189             LOCAL_STDERR.with(|slot| {
 190                 *slot.borrow_mut() = s.take();
 191             });
 192         }
 193         (None, Some(ref mut err)) => { write(err) }
 194         _ => {}
 195     }
 196 }
 197
 198 pub fn on_panic(obj: &(Any+Send), file: &'static str, line: u32) {
 199     let panics = PANIC_COUNT.with(|s| {
 200         let count = s.get() + 1;
 201         s.set(count);
 202         count
 203     });
 204
 205     // If this is the third nested call, on_panic triggered the last panic,
 206     // otherwise the double-panic check would have aborted the process.
 207     // Even if it is likely that on_panic was unable to log the backtrace,
 208     // abort immediately to avoid infinite recursion, so that attaching a
 209     // debugger provides a useable stacktrace.
 210     if panics >= 3 {
 211         util::dumb_print(format_args!("thread panicked while processing \
 212                                        panic. aborting.\n"));
 213         unsafe { intrinsics::abort() }
 214     }
 215
 216     let info = PanicInfo {
 217         payload: obj,
 218         location: Location {
 219             file: file,
 220             line: line,
 221         },
 222     };
 223
 224     unsafe {
 225         let _lock = HOOK_LOCK.read();
 226         match HOOK {
 227             Hook::Default => default_hook(&info),
 228             Hook::Custom(ptr) => (*ptr)(&info),
 229         }
 230     }
 231
 232     if panics >= 2 {
 233         // If a thread panics while it's already unwinding then we
 234         // have limited options. Currently our preference is to
 235         // just abort. In the future we may consider resuming
 236         // unwinding or otherwise exiting the thread cleanly.
 237         util::dumb_print(format_args!("thread panicked while panicking. \
 238                                        aborting.\n"));
 239         unsafe { intrinsics::abort() }
 240     }
 241 }